Perioperative hypothermia in geriatric orthopedic patients assessed by continuous zero-heat-flux monitoring: a prospective observational study

Perioperative hypothermia in geriatric orthopedic patients assessed by continuous zero-heat-flux monitoring: a prospective observational study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Perioperative hypothermia in geriatric orthopedic patients assessed by continuous zero-heat-flux monitoring: a prospective observational study Melike Ayça Keçeli, Özal Adıyeke This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9118190/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Background: Hypothermia, defined as core body temperature below 36°C, is a frequent complication in patients under general anesthesia and is closely associated with cardiovascular morbidity, perioperative hemorrhagic complications, impaired drug metabolism, and surgical site infection. Its impact is more pronounced in geriatric patients due to age-related physiological alterations including blunted thermoregulatory responses, sarcopenia, and reduced subcutaneous adipose tissue. Objective: This study aimed to determine the incidence of inadvertent perioperative hypothermia in geriatric patients (≥65 years) undergoing orthopedic surgery under general or regional anesthesia, using continuous non-invasive core temperature monitoring via the zero-heat-flux (ZHF) method, and to identify associated risk factors. Methods: A prospective observational study was conducted between February and May 2018 at Istanbul Kanuni Sultan Suleyman Research and Training Hospital following ethics committee approval (Protocol No. 2018/292). A total of 87 patients aged ≥65 years undergoing orthopedic surgery with an expected duration ≥30 minutes were enrolled. Core temperature was monitored continuously from the premedication room through PACU discharge using the SpotOn™ Zero-Heat-Flux sensor (3M, St. Paul, USA). Active warming (Bair Hugger forced-air system, 3M) was applied to all patients. Statistical analyses included chi-square, Fisher's exact test, t-test, Pearson correlation, and SPSS v22.0 (significance: p<0.05). Results: Of the 87 patients (62 female, 25 male; mean age 74.3 ± 7,5 years), intraoperative hypothermia was detected in 51.7% (n=45; 95% CI 41.2–62.2%) and postoperative hypothermia in 46.0% (n=40; 95% CI 35.5–56.5%). Mean preoperative temperature was 36.84 ± 0.50°C; mean intraoperative temperature 36.29 ± 0.65°C; mean PACU temperature 35.91 ± 0.83°C. Temperature drops of 0.5°C, 1°C, 1.5°C, 2°C, and 2.5°C occurred at a mean of 27.6, 48.8, 63.9, 88.0, and 91.1 minutes, respectively. Significant risk factors for intraoperative hypothermia included: prolonged surgery (>90 min, 66.7%; OR 4.00, 95% CI 1.63–9.80; p<0.001), general anesthesia (OR 5.43, 95% CI 1.11–26.52; p1000 ml (OR 3.67, 95% CI 1.49–9.02; p=0.019), ASA II and IV status (p<0.05), and total knee arthroplasty (p<0.05). Higher preoperative body temperature was protective (p<0.001). Hypothermic patients had significantly longer PACU recovery times (p=0.021). Conclusion: Perioperative hypothermia is highly prevalent in geriatric orthopedic patients even when active warming protocols are in use. General anesthesia, prolonged surgery, high ASA score, large fluid volumes, and low preoperative body temperature are key risk factors. Continuous non-invasive ZHF core temperature monitoring enables early detection. Strict adherence to warming protocols, use of prewarmed IV fluids, and interdisciplinary collaboration are essential to reduce hypothermia and its associated morbidity in this vulnerable population. geriatrics hypothermia thermoregulation perioperative temperature monitoring zero-heat-flux orthopedic surgery anesthesia Figures Figure 1 1. Introduction With advances in medicine, technology, and preventive healthcare, global life expectancy has increased substantially, resulting in a growing proportion of elderly individuals presenting for surgical procedures. According to the World Health Organization (WHO), the geriatric age threshold is defined as 65 years. Globally, the number of people aged 65 years and older is projected to rise from 703 million in 2019 to 1.5 billion by 2050 — representing a shift from 1 in 11 to 1 in 6 of the world's population - with the fastest growth occurring in low- and middle-income countries [ 1 ]. Advanced age is no longer considered an absolute contraindication for surgery, and increasingly major orthopedic procedures are being performed in this group [ 2 , 3 ]. Inadvertent perioperative hypothermia (IPH) — defined as a core body temperature below 36°C occurring between one hour before anesthesia induction and 24 hours postoperatively — is one of the most common yet preventable complications in surgical patients [ 4 , 5 ]. Its reported incidence varies widely, from 4% to as high as 90%, depending on the patient population, anesthetic technique, surgical setting, and monitoring method [ 6 – 8 ]. Both the American Society of Anesthesiologists (ASA) and the National Institute for Health and Care Excellence (NICE) recommend routine intraoperative temperature monitoring and active warming to prevent IPH [ 9 , 10 ]. In Turkey, the Turkish Society of Anesthesiology and Reanimation (TARD) published its 'Prevention of Inadvertent Perioperative Hypothermia' guideline in 2013. Thermoregulation in humans is governed by the anterior hypothalamus, which maintains core temperature within a narrow range of 36.5–37.3°C with circadian variation of only 0.5–0.8°C. Anesthesia disrupts this regulation across all age groups; however, the effect is more pronounced in geriatric patients due to age-related blunting of vasoconstrictive and shivering responses, reduced metabolic rate, loss of subcutaneous fat, and sarcopenia [ 11 , 12 ]. The vasoconstrictive threshold decreases by approximately 1°C in individuals between 60 and 80 years of age. The clinical consequences of IPH are well established and include: increased incidence of surgical site infection, coagulopathy (platelet dysfunction, reduced clotting factor activity), cardiac morbidity (arrhythmias, myocardial ischemia), impaired drug metabolism (prolonged neuromuscular blockade, extended sedative effects), postoperative shivering, prolonged PACU stay, and increased healthcare costs [ 13 – 17 ]. While prior studies have examined perioperative hypothermia, a notable methodological limitation has been the use of intermittent, indirect, or invasive temperature measurement methods (axillary, tympanic, esophageal) that may fail to accurately reflect true core temperature. The zero-heat-flux (ZHF) method, employing the SpotOn™ sensor applied to the frontotemporal region, creates an isothermal pathway that provides validated, continuous, non-invasive core temperature estimation comparable to esophageal measurement. The primary aims of this study were: (1) to determine the incidence of inadvertent perioperative hypothermia using continuous ZHF non-invasive core temperature monitoring in geriatric orthopedic patients; (2) to characterize the time course of intraoperative temperature decline; and (3) to identify modifiable and non-modifiable risk factors. To our knowledge, only a limited number of studies have used continuous ZHF monitoring for this specific patient population. 2. Materials and Methods 2.1 Study Design, Setting, and Ethics This was a prospective, observational, single-blind study conducted at Istanbul Kanuni Sultan Suleyman Training and Research Hospital, University of Health Sciences, Istanbul, Turkey. Ethical approval was obtained from the Clinical Research Ethics Committee of Istanbul Bakirkoy Dr. Sadi Konuk Training and Research Hospital (Protocol No. 2018/292; Decision date: 29.01.2018). Written informed consent was obtained from all patients. The study was conducted in accordance with the Declaration of Helsinki. The anesthesia team and surgical staff were blinded to the study to allow unbiased observation of standard clinical practice. 2.2 Patient Selection Between February and May 2018, a total of 726 patients who underwent orthopedic surgery at the study institution were screened for eligibility. Of these, 639 patients did not meet the inclusion criteria (age < 65 years, expected surgery duration < 30 minutes, or anesthesia type other than general or regional) and were not assessed further. Of the remaining 87 patients assessed for eligibility, 10 were excluded for the following reasons: use of corticosteroids or immunosuppressive medications (n = 2), preoperative core temperature 38°C (n = 3), and planned local anesthesia only or refusal to provide written informed consent (n = 5). Accordingly, 87 patients who met all eligibility criteria were enrolled and completed the study (Fig. 1). Inclusion criteria: age ≥ 65 years; ASA physical status I–IV; elective or emergency orthopedic procedure with expected duration ≥ 30 minutes; provision of written informed consent. Exclusion criteria: use of corticosteroids or immunosuppressive medications; preoperative core temperature 38°C; planned local anesthesia only; refusal to participate. 2.3 Anesthesia Protocols Anesthetic technique was determined by the attending anesthesiologist based on patient condition and procedure type. General anesthesia (n = 12, 13.8%): Preoxygenation for 3 minutes with 100% oxygen, then induction with propofol 2–3 mg/kg IV (Propofol 1%, Fresenius Kabi), fentanyl 1 mcg/kg IV (Talinat 0.5 mg/10 ml, Vem), and rocuronium 0.6–1.2 mg/kg IV (Muscuron 50 mg/5 ml, Kocak Farma). Maintenance: 2% sevoflurane in 50% O2/air mixture at 4 L/min total fresh gas flow via mechanical ventilation. Hypobaric spinal anesthesia (n = 29, 33.3%): Sitting or lateral position; 25G Quincke needle (Egemen, Turkey) at L3–L4 or L4–L5 interspace; intrathecal injection of 17.5 mg marcaine (Marcaine 0.5%, AstraZeneca) + 32 mcg fentanyl (Talinat) + 1.3 ml sterile water for injection. Patient maintained in lateral decubitus (operative side uppermost) for 7 minutes. Hyperbaric spinal anesthesia (n = 44, 50.6%): Same needle technique; intrathecal injection of 13 mg Heavy Marcaine (Marcaine Spinal Heavy 0.5%, AstraZeneca). Peripheral nerve block: n = 2 (2.3%). Premedication with midazolam 0.5 mg/kg IV (Zolamid 5 mg/5 ml, Defarma) was administered to 54 patients (62.1%). All IV fluids, blood products, and irrigation solutions were maintained at room temperature. All patients received passive warming (one 100% cotton blanket) in the premedication room and active warming (Bair Hugger forced-air warming system, 3M) intraoperatively per TARD guidelines until core temperature reached 37°C. Patients received supplemental oxygen by mask at 4 L/min throughout. 2.4 Temperature Monitoring and Data Collection Core body temperature was continuously monitored from the premedication room through PACU discharge using the SpotOn™ Zero-Heat-Flux Temperature Monitoring System (3M, St. Paul, USA) applied to the frontotemporal region. This device provides non-invasive, continuous core temperature measurement validated against esophageal and pulmonary artery catheter measurements. Hypothermia was defined as core temperature < 36°C at any measurement point. A standardized data collection form was completed by the same study anesthesiologist throughout. Data recorded included: demographics (age, sex, BMI), ASA status, diagnosis, procedure type (elective/emergency), anesthesia type, premedication, anesthesia and surgery duration, IV fluid and blood product volumes with timing, and the operative minute at which temperature decrements of 0.5°C, 1.0°C, 1.5°C, 2.0°C, 2.5°C, and 3.0°C occurred. Room temperatures (premedication room, OR, PACU) were measured every 15 minutes using a TM898 digital thermometer (TT-TECHNIC, China). PACU discharge was based on modified Aldrete score ≥ 9. 2.5 Statistical Analysis Data were analyzed using IBM SPSS Statistics v22.0. Categorical variables are presented as frequencies and percentages; continuous variables as mean ± standard deviation (SD). Between-group comparisons for categorical variables used Pearson chi-square and Fisher's exact tests. Continuous variables were compared by independent samples t-test. Correlations between continuous variables were assessed by Pearson correlation analysis. Odds ratios (OR) with 95% confidence intervals (CI) were calculated using standard 2×2 contingency tables for primary binary risk factor comparisons. Statistical significance was set at p < 0.05. No a priori sample size calculation was performed as this was a prospective consecutive-enrollment observational study. Post-hoc power analysis confirmed that the enrolled sample of n = 87 exceeded the minimum required sample size of n = 63 (reference incidence: 43.9% [ 18 ] vs observed 51.7%; α = 0.05; power = 0.80). For the primary subgroup comparison of surgery duration (> 90 min vs ≤ 90 min), achieved statistical power was 87.2%. 3. Results 3.1 Demographics and Patient Characteristics Of the 726 patients screened during the study period, 87 were enrolled and all completed the study with full data collection (100% follow-up; Fig. 1). Ten patients were excluded prior to enrollment: 2 for corticosteroid or immunosuppressive medication use, 3 for preoperative core temperature outside the 36–38°C range, and 5 for planned local anesthesia or refusal to consent. The 87 enrolled patients comprised 62 female (71.3%) and 25 male (28.7%). Age distribution: 38 patients (43.7%) were 65–74 years, 36 (41.4%) were 75–84 years, and 13 (14.9%) were ≥ 85 years. BMI distribution: underweight (< 18.5 kg/m²) n = 2 (2.3%); normal weight (18.5–24.99) n = 27 (31.0%); overweight (25–29.99) n = 31 (35.6%); obese (≥ 30) n = 27 (31.0%). ASA status: II in 29 (33.3%), III in 56 (64.4%), and IV in 2 (2.3%). Surgical procedures: total knee arthroplasty (TKA) n = 42 (48.3%), proximal femur nailing (PFN) n = 19 (21.8%), partial hip arthroplasty n = 12 (13.8%), total hip arthroplasty n = 5 (5.7%), lower extremity surgery n = 4 (4.6%), other orthopedic procedures n = 4 (4.6%), upper extremity surgery n = 1 (1.1%). Emergency procedures: n = 5 (5.7%); elective: n = 82 (94.3%). Premedication with midazolam was administered in 54 patients (62.1%). Anesthesia duration distribution: 0–60 minutes in 14 (16.1%), 61–90 minutes in 25 (28.7%), 91–120 minutes in 28 (32.2%), and > 120 minutes in 20 (23.0%). Mean surgery duration: 98.07 ± 32.7 minutes. IV fluid volumes administered: 0–1000 ml in 36 (41.4%), 1000–1500 ml in 34 (39.1%), 1500–2000 ml in 14 (16.1%), 2000–2500 ml in 3 (3.4%). Table 1 Patient demographics and baseline characteristics (n = 87) Variable n (%) Mean ± SD Sex: Female / Male 62 (71.3%) / 25 (28.7%) — Age: years — 74.3 ± 7,5 Age: 65–74 years 38 (43.7%) — Age: 75–84 years 36 (41.4%) — Age: ≥85 years 13 (14.9%) — BMI: Normal (18.5–24.99) 27 (31.0%) — BMI: Overweight (25–29.99) 31 (35.6%) — BMI: Obese (≥ 30) 27 (31.0%) — ASA II / III / IV 29 (33.3%) / 56 (64.4%) / 2 (2.3%) — General anesthesia 12 (13.8%) — Hypobaric spinal anesthesia 29 (33.3%) — Hyperbaric spinal anesthesia 44 (50.6%) — Peripheral nerve block 2 (2.3%) — Total knee arthroplasty 42 (48.3%) — Proximal femur nailing 19 (21.8%) — Mean anesthesia duration — 98.07 ± 32.7 min Preop waiting time (premedication room) — 16.78 ± 11.89 min PACU recovery time — 27.86 ± 15.82 min ASA = American Society of Anesthesiologists; BMI = Body Mass Index; PACU = Post-Anesthesia Care Unit; SD = Standard Deviation. 3.2 Environmental Temperatures Mean premedication room temperature: 23.71 ± 0.81°C. Mean operating room temperature: 19.61 ± 1.38°C. Mean PACU temperature: 24.23 ± 1.84°C. 3.3 Perioperative Core Temperature Profiles Mean preoperative core temperature (premedication room): 36.84 ± 0.50°C. Mean intraoperative core temperature: 36.29 ± 0.65°C. Mean PACU core temperature: 35.91 ± 0.83°C. Mean OR exit temperature: 35.97 ± 0.84°C. Mean PACU exit temperature: 35.90 ± 0.82°C. Table 2 Core temperatures and unit stay times by perioperative phase Phase / Unit Mean Temperature ± SD (°C) Mean Exit Temperature ± SD (°C) Mean Stay Duration ± SD Premedication Room 36.84 ± 0.50 36.84 ± 0.51 16.78 ± 11.89 min Operating Room (intraoperative) 36.29 ± 0.65 35.97 ± 0.84 98.07 ± 32.70 min PACU (post-anesthesia care unit) 35.91 ± 0.83 35.90 ± 0.82 27.86 ± 15.82 min SD = Standard Deviation; PACU = Post-Anesthesia Care Unit. 3.4 Incidence of Perioperative Hypothermia Intraoperative hypothermia (core temperature < 36°C during surgery) was detected in 45 patients (51.7%). At OR exit, 40 patients (46.0%) were hypothermic. Among patients who were hypothermic intraoperatively, 40 remained hypothermic at OR exit; 5 had recovered to normothermia. All 42 patients who were normothermic intraoperatively remained normothermic at OR exit. Table 3 Incidence of intraoperative and postoperative hypothermia Outcome Normothermia n (%) Hypothermia n (%) Intraoperative (during surgery) 42 (48.3%) 45 (51.7%) At OR exit (postoperative) 47 (54.0%) 40 (46.0%) Hypothermia defined as core temperature < 36°C. 3.5 Time Course of Intraoperative Temperature Decline Continuous ZHF monitoring permitted precise determination of the operative minute at which successive temperature decrements occurred. A 0.5°C drop occurred at a mean of 27.61 ± 18.54 minutes; 1.0°C at 48.80 ± 22.23 minutes; 1.5°C at 63.86 ± 32.53 minutes; 2.0°C at 88.00 ± 15.89 minutes; and 2.5°C at 91.12 ± 35.03 minutes of surgery. Table 4 Mean operative time at which successive core temperature decrements were reached Temperature Decrement Mean Time ± SD (minutes) 0.5°C decrease 27.61 ± 18.54 1.0°C decrease 48.80 ± 22.23 1.5°C decrease 63.86 ± 32.53 2.0°C decrease 88.00 ± 15.89 2.5°C decrease 91.12 ± 35.03 SD = Standard Deviation. Times represent the mean operative minute at which the specified decrement from baseline was first recorded. 3.6 Risk Factors for Perioperative Hypothermia Surgery duration: Intraoperative hypothermia incidence was 20.0% for procedures 90 minutes (p < 0.001). At OR exit, hypothermia also increased significantly with procedure duration (p = 0.003). A negative correlation of 45.9% was found between surgery duration and OR exit temperature (p 90 minutes had significantly higher odds of intraoperative hypothermia compared to those with procedures ≤ 90 minutes (OR 4.00, 95% CI 1.63–9.80). Preoperative body temperature: Higher preoperative temperature was significantly associated with lower intraoperative hypothermia incidence (p < 0.001) and lower postoperative hypothermia incidence (p < 0.001). Anesthesia type: Patients under general anesthesia had significantly higher intraoperative hypothermia incidence compared to regional anesthesia patients (p < 0.05). Intraoperative hypothermia incidence under general anesthesia was 83.3% (10/12), versus 37.9% (11/29) for hypobaric spinal and 54.5% (24/44) for hyperbaric spinal anesthesia. General anesthesia was associated with over five-fold higher odds of intraoperative hypothermia compared to regional anesthesia (OR 5.43, 95% CI 1.11–26.52). At OR exit, general anesthesia was also associated with significantly higher hypothermia (p < 0.05). No statistically significant difference was found between hypobaric and hyperbaric spinal anesthesia in hypothermia incidence. Surgical procedure: Patients undergoing total knee arthroplasty and procedures other than proximal femur nailing had significantly higher intraoperative hypothermia incidence (p < 0.05). Proximal femur nailing and lower extremity procedures were associated with significantly lower hypothermia incidence (p < 0.05). Postoperatively, proximal femur nailing was also associated with significantly lower hypothermia (p < 0.05). ASA score: ASA II and ASA IV patients had significantly higher intraoperative hypothermia incidence compared to ASA III patients (p < 0.05). IV fluid volume: Significant association was found between intraoperative hypothermia and IV fluid volume administered (chi-square = 9.934; p = 0.019). Hypothermia incidence was 33.3% (12/36) in patients receiving 0–1000 ml, 61.8% (21/34) in those receiving 1000–1500 ml, 64.3% (9/14) in those receiving 1500–2000 ml, and 100% (3/3) in those receiving 2000–2500 ml. Patients receiving > 1000 ml of IV fluid had significantly higher odds of intraoperative hypothermia compared to those receiving ≤ 1000 ml (OR 3.67, 95% CI 1.49–9.02). Sex: While no significant association was found between sex and intraoperative hypothermia, male patients had significantly higher hypothermia incidence at OR exit compared to female patients (p < 0.05). PACU recovery time: Patients who were hypothermic intraoperatively had significantly longer PACU recovery times compared to normothermic patients (p = 0.021). Room temperature: No statistically significant correlation was found between premedication room temperature and intraoperative or OR-exit body temperature (p > 0.05). Similarly, no significant correlation was found between mean OR temperature and OR-exit body temperature (p > 0.05). Table 5 Significant risk factors for intraoperative and postoperative hypothermia with odds ratios Risk Factor Intraop. Hypothermia Incidence OR (95% CI) Postop. Hypothermia p-value Surgery > 90 min 66.7% (32/48) 4.00 (1.63–9.80) Significant p < 0.001 / p = 0.003 General anesthesia 83.3% (10/12) 5.43 (1.11–26.52) Significant p < 0.05 ASA II or IV status Elevated vs ASA III —* — p < 0.05 Total knee arthroplasty Elevated vs other —* — p 1000 ml 62–100% (33/51) 3.67 (1.49–9.02) — p = 0.019 High preop temperature Protective — Protective p < 0.001 Proximal femur nailing Reduced — Reduced p < 0.05 Male sex NS (intraop) — Elevated p < 0.05 PACU recovery (hypothermic pts) — — Prolonged p = 0.021 OR = odds ratio; CI = confidence interval; NS = not statistically significant; IV = intravenous; ASA = American Society of Anesthesiologists. *OR not calculable due to multi-category comparison or insufficient cell counts. 4. Discussion This prospective observational study demonstrated that inadvertent perioperative hypothermia remains highly prevalent in geriatric orthopedic patients even when active warming protocols are in use, affecting 51.7% intraoperatively and 46.0% at OR exit. These findings are consistent with a large multicenter observational study by Alfonsi et al. [ 19 ], which reported a perioperative hypothermia prevalence of 53.5% on admission to the recovery room across 52 centers in France, despite active warming device use in 90.4% of patients — reinforcing that protocol adherence rather than device availability is the key determinant of hypothermia prevention. The somewhat higher rate in our study likely reflects the older patient population (mean age 74.3 years), lower ambient OR temperature (19.6°C), and the inability to warm IV fluids. A key methodological strength distinguishing this study is the use of continuous ZHF non-invasive core temperature monitoring. Unlike intermittent axillary or tympanic measurements — which underestimate core temperature by 1–4°C — ZHF monitoring provides validated continuous data comparable to esophageal thermometry. This allowed precise characterization of the temperature decline time course: a 0.5°C drop at ~ 28 minutes, 1.0°C at ~ 49 minutes, 1.5°C at ~ 64 minutes, 2.0°C at ~ 88 minutes and 2.5°C at ~ 91 minutes. These kinetics are consistent with the three-phase model of general anesthetic hypothermia described by Sessler [ 20 ]: rapid redistribution in Phase I (first 30–45 min), linear decline in Phase II, and plateau in Phase III with peripheral vasoconstriction. The validity and clinical applicability of the ZHF method (SpotOn™, 3M) have been evaluated in several independent studies. Iden et al. [ 21 ] compared SpotOn with sublingual and nasopharyngeal sensors in 120 gynecological and trauma surgery patients, concluding that ZHF offers sufficient accuracy for routine clinical use. Boisson et al. [ 22 ] demonstrated in a prospective observational study that ZHF was a practical, non-invasive alternative to esophageal measurement across all perioperative phases, with the study becoming one of the most cited in ZHF validation literature. A multicenter study (ESOSPOT, NCT03820232) further confirmed the clinical acceptability of ZHF core temperature estimation against esophageal thermometry during major elective surgery [ 23 , 24 ]. These validation data provide a strong methodological foundation for the findings reported in the present study. To date, only a limited number of prospective studies have specifically employed ZHF monitoring in orthopedic surgical populations. Munday et al. [ 25 ] evaluated ZHF accuracy against esophageal thermometry in 30 patients undergoing upper and lower limb orthopedic surgery and observed that device bias was temperature-dependent — a finding particularly relevant to the geriatric patient group where mild hypothermia predominates. Of direct relevance to the present study, Park et al. [ 26 ] conducted a prospective comparison of ZHF (SpotOn), tympanic membrane, and bladder thermometry in patients aged ≥ 80 years undergoing lower extremity orthopedic surgery. Their critical finding was that hypothermia was detectable by both ZHF and bladder sensors at approximately 100–110 minutes intraoperatively, whereas tympanic measurement failed to identify hypothermia in the same cohort — underscoring the superiority of ZHF for hypothermia detection in elderly orthopedic patients and directly validating the monitoring approach used in the current study. In the Turkish literature, Duman et al. [ 27 ] previously reported hypothermia incidence and risk factors in orthopedic surgery, albeit using conventional measurement methods. More recently, a study from Dokuz Eylül University [ 28 ] employed SpotOn ZHF monitoring in major abdominal oncologic surgery, reporting a PACU hypothermia incidence of 38.1% and identifying absence of preoperative pre-warming and higher ASA score as leading risk factors — findings broadly consistent with the present study. To the best of our knowledge, the current study remains one of the few to apply continuous ZHF monitoring specifically in a geriatric orthopedic cohort in Turkey, and the only study to provide detailed intraoperative temperature decline kinetics in this population. The significantly higher hypothermia incidence under general anesthesia (83.3%) versus regional anesthesia (37.9–54.5%) in our cohort corroborates findings from Frisch et al. [ 18 ], who reported a 43.9% hypothermia rate in total hip arthroplasty and 32.6% in total knee arthroplasty. General anesthetics raise the interthreshold range from 0.2°C to up to 4°C by suppressing hypothalamic regulation in a dose-dependent manner, inhibiting vasoconstriction and shivering — the two primary heat-conserving responses. Regional anesthesia causes peripheral vasodilation and impairs thermoregulation below the block level, but preserves some central thermoregulatory capacity, resulting in a less severe but still significant hypothermic pattern [ 29 ]. The lack of significant difference between hypobaric and hyperbaric spinal anesthesia in our study supports the view that the extent of sympathetic blockade — rather than the baricity of the local anesthetic — determines thermoregulatory impairment during neuraxial anesthesia. Both techniques produced similar rates of hypothermia, a finding with direct clinical implications for practice. The strong positive correlation between IV fluid volume and hypothermia (p = 0.019) is consistent with Yi et al. [ 30 ], who demonstrated that unwarmed fluid infusion of ≥ 1000 ml significantly increases hypothermia incidence. The administration of room-temperature (19–23°C) IV fluids, as was standard practice in our setting, represents a major and modifiable source of perioperative heat loss. Campbell et al. [ 31 ] demonstrated in a Cochrane review of 25 trials (1250 patients) that warming IV fluids to 37–41°C significantly attenuates core temperature decline compared to room-temperature administration. The association of total knee arthroplasty with higher hypothermia incidence compared to proximal femur nailing is likely attributable to multiple factors: longer typical procedure duration, more extensive tissue exposure, greater tourniquet-related blood redistribution, and higher IV fluid requirements in TKA. The protective effect of higher preoperative temperature reinforces the rationale for pre-warming in the premedication room, which reduces the core-to-peripheral gradient and thereby limits redistribution-induced heat loss in Phase I of anesthesia [ 32 ]. The finding that male sex was associated with higher postoperative hypothermia (OR-exit) but not intraoperative hypothermia is noteworthy and consistent with Panagiotis et al. [ 33 ]. Although women have higher body fat percentage (which provides better thermal insulation), they have lower muscle mass (reducing thermogenic capacity) and greater body surface area relative to volume — factors that may offset each other intraoperatively but become relevant postoperatively as active warming is withdrawn. Hypothermic patients had significantly prolonged PACU recovery times (p = 0.021), adding to the body of evidence linking IPH to increased healthcare resource utilization. Longer PACU stays increase nursing workload, delay ward bed availability, and contribute to healthcare costs — effects that are amplified in high-volume orthopedic units serving geriatric patients. A limitation of this study is its single-center, observational design without a control arm without warming. The inability to warm IV fluids due to institutional resource constraints — which likely increased hypothermia rates — and the lack of 24-hour postoperative temperature follow-up represent the main limitations. It should also be noted that while ZHF has been validated against esophageal thermometry across diverse surgical settings [ 20 – 22 , 24 ], simultaneous comparative esophageal monitoring was not performed in the current study. Future multicenter randomized trials should evaluate the combined impact of IV fluid warming, preoperative forced-air pre-warming, and individualized warming protocols in geriatric orthopedic surgery, with continuous ZHF monitoring as the standard temperature assessment method. Regarding generalisability, the findings of this study are most directly applicable to geriatric patients (≥ 65 years) undergoing lower extremity orthopedic surgery in tertiary care settings with similar resource and environmental conditions. The observed hypothermia rates may differ in institutions with higher baseline operating room temperatures, routine IV fluid warming, or more aggressive pre-warming protocols. Physiological and anthropometric differences across ethnic populations may also influence thermoregulatory responses; therefore, extrapolation to non-Turkish or non-geriatric populations should be made with caution. Nevertheless, the identified risk factors — particularly anesthesia type, surgery duration, and IV fluid volume — are consistent with findings from diverse international cohorts and are likely to be broadly generalizable across surgical settings. 5. Conclusion This prospective study confirms that perioperative hypothermia is a serious, prevalent, and clinically significant complication in geriatric patients undergoing orthopedic surgery, affecting more than half of patients intraoperatively and nearly half at OR exit despite active and passive warming measures. Key modifiable risk factors include general anesthesia, prolonged operative duration, unwarmed IV fluid volumes exceeding 1000 ml, and low preoperative body temperature. Continuous non-invasive ZHF core temperature monitoring enables early detection and timely intervention. Universal adherence to perioperative warming guidelines, routine warming of IV fluids, and interdisciplinary collaboration with the surgical team are strongly recommended to reduce the burden of this preventable complication in the geriatric orthopedic population. Declarations Ethics Approval: Istanbul Bakirkoy Dr. Sadi Konuk Training and Research Hospital Clinical Research Ethics Committee; Protocol No. 2018/292; Approval date 29.01.2018. Informed Consent: Written informed consent was obtained from all participants prior to enrollment. Funding: This research received no external funding. No pharmaceutical or device company funding was received. Conflicts of Interest: The authors declare no conflicts of interest. Author Contributions: MAK: study design, data collection, data analysis, manuscript drafting. ÖA: supervision, critical revision. All authors approved the final manuscript. References United Nations Department of Economic and Social Affairs, Population Division. World Population Ageing 2019: Highlights. New York: United Nations; 2019. https://www.un.org/en/development/desa/population/publications/pdf/ageing/WorldPopulationAgeing2019-Highlights.pdf Memtsoudis SG, Stundner O, Rasul R, Chiu YL, Sun X, Ramachandran SK, Fleischut P, Danninger T. Trends in the incidence and in-hospital outcomes of elective major orthopaedic surgery in patients eighty years of age and older in the United States from 2000 to 2009. J Bone Joint Surg Am. 2014;96(14):e120. doi: 10.2106/JBJS.M.01266. PMID: 25031373. Can SO, Genc ST, Okten F. Anaesthesia management in geriatric orthopedic surgery patients: general or regional. Turk Klin J Anest Reanim. 2004;2:161-170. Turkish Society of Anaesthesiology and Reanimation Practice Guideline for Prevention of Unintentional Perioperative Hypothermia. Turk J Anaesth Reanim. 2013;41:188–190. Torossian, A. Thermal management during anaesthesia and thermoregulation standards for the prevention of inadvertent perioperative hypothermia. Best Pract Res Clin Anaesthesiol. 2008;22(4):659-668. Leslie, K., Sessler, D.I. Perioperative hypothermia in the high-risk surgical patient. Best Pract Res Clin Anaesthesiol 17, 485–498 (2003). https://doi.org/10.1016/S1521-6896(03)00049-0 Burger, L., Fitzpatrick, J. Prevention of inadvertent perioperative hypothermia. Br J Nurs 18, 1114–1119 (2009). https://doi.org/10.12968/bjon.2009.18.18.44553 Tappen, R.M., Andre, S.P. Inadvertent hypothermia in elderly surgical patients. AORN J 63, 639–644 (1996). https://doi.org/10.1016/S0001-2092(06)63431-3 Addendum to Clinical Guideline CG65, Inadvertent Perioperative Hypothermia. London: National Institute for Health and Care Excellence (NICE); 2016 Dec. PMID: 31825571. American Society of Anesthesiologists Committee on Standards and Practice Parameters. Standards for Basic Anesthetic Monitoring. Approved by the ASA House of Delegates, October 21, 1986; last amended October 20, 2010; effective July 1, 2011. Park Ridge (IL): ASA; 2011. Available at: https://www.asahq.org/standards-and-practice-parameters/standards-for-basic-anesthetic-monitoring Frank, S.M., Fleisher, L.A., Breslow, M.J. et al. Perioperative maintenance of normothermia reduces the incidence of morbid cardiac events: a randomized clinical trial. JAMA 277, 1127–1134 (1997). https://doi.org/10.1001/jama.1997.03540380041029 Van Someren, E.J. Thermoregulation and aging. Am J Physiol Regul Integr Comp Physiol 292, R99–R102 (2007). https://doi.org/10.1152/ajpregu.00557.2006 Schmied, H., Reiter, A., Kurz, A., Sessler, D.I., Kozek, S. Mild hypothermia increases blood loss and transfusion requirements during total hip arthroplasty. Lancet 347, 289–292 (1996). https://doi.org/10.1016/S0140-6736(96)90466-3 Winkler, M., Akça, O., Birkenberg, B. et al. Aggressive warming reduces blood loss during hip arthroplasty. Anesth Analg 91, 978–984 (2000). https://doi.org/10.1097/00000539-200010000-00038 Heier, T., Caldwell, J.E., Sessler, D.I., Miller, R.D. Mild intraoperative hypothermia increases duration of action of vecuronium blockade. Anesthesiology 74, 815–819 (1991). https://doi.org/10.1097/00000542-199105000-00007 Kurz, A., Sessler, D.I., Lenhardt, R. Perioperative normothermia to reduce the incidence of surgical-wound infection. N Engl J Med 334, 1209–1216 (1996). https://doi.org/10.1056/NEJM199605093341901 Forbes, S.S., Eskicioglu, C., Nathens, A.B. et al. Evidence-based guidelines for prevention of perioperative hypothermia. J Am Coll Surg 209, 492–503 (2009). https://doi.org/10.1016/j.jamcollsurg.2009.07.002 Frisch, N.B., Pepper, A.M., Rooney, E., Silverton, C. Intraoperative hypothermia in total hip and knee arthroplasty. Orthopedics 40, 56–63 (2017). https://doi.org/10.3928/01477447-20161031-04 Alfonsi P, Bekka S, Aegerter P; SFAR Research Network investigators. Prevalence of hypothermia on admission to recovery room remains high despite a large use of forced-air warming devices: findings of a non-randomized observational multicenter and pragmatic study on perioperative hypothermia prevalence in France. PLoS One. 2019;14(12):e0226038. doi: 10.1371/journal.pone.0226038. PMID: 31869333; PMCID: PMC6927638. Sessler, D.I. Temperature monitoring and perioperative thermoregulation. Anesthesiology 109, 318–338 (2008). https://doi.org/10.1097/ALN.0b013e31817f6d76 Iden, T., Horn, E.P., Bein, B., Böhm, R., Beese, J., Höcker, J. Intraoperative temperature monitoring with zero heat flux technology (3M SpotOn sensor) in comparison with sublingual and nasopharyngeal temperature: a prospective observational study. Eur J Anaesthesiol 32, 387–391 (2015). https://doi.org/10.1097/EJA.0000000000000232 Boisson M, Alaux A, Kerforne T, Mimoz O, Debaene B, Dahyot-Fizelier C, Frasca D. Intra-operative cutaneous temperature monitoring with zero-heat-flux technique (3M SpotOn) in comparison with oesophageal and arterial temperature: a prospective observational study. Eur J Anaesthesiol. 2018;35(11):825-830. doi:10.1097/EJA.0000000000000822. Eshraghi, Y., Nasr, V., Parra-Sanchez, I. et al. An evaluation of a zero-heat-flux cutaneous thermometer in cardiac surgical patients. Anesth Analg 119, 543–549 (2014). https://doi.org/10.1213/ANE.0000000000000319 Liang H, Wang JY, Liang Y, Shao XF, Ding YL, Jia HQ. Agreement of zero-heat-flux thermometry with the oesophageal and tympanic core temperature measurement in patient receiving major surgery. J Clin Monit Comput. 2024 Feb;38(1):197-203. doi: 10.1007/s10877-023-01078-2. Epub 2023 Oct 4. PMID: 37792140; PMCID: PMC10879315. Munday J, Higgins N, Jones L, Vagenas D, Van Zundert A, Keogh S. Zero-heat-flux and esophageal temperature monitoring in orthopedic surgery: an observational study. J Multidiscip Healthc. 2021;14:1819–1827. doi: 10.2147/JMDH.S313310. PMID: 34285500; PMCID: PMC8286425. Park C, Kim T, Oh S, Bang YS. Prospective comparative analysis of zero-heat-flux thermometer (SpotOn®) compared with tympanic thermometer and bladder thermometer in extremely aged patients undergoing lower extremity orthopedic surgery. Medicine (Baltimore). 2023 Oct 20;102(42):e35593. doi: 10.1097/MD.0000000000035593. PMID: 37861486; PMCID: PMC10589526. Duman AY, Yılmaz E. Incidence of perioperative hypothermia in orthopaedic surgery and risk factors. Cukurova Med J. 2016;41(4):687-694. Aksu Erdost H, Özkardeşler S, Değirmenci AK, Dalak RM, Terzi C. Intraoperative Temperature Monitoring with Zero Heat Flux Technology (3M SpotOn Sensor) in Comparison with Tympanic and Oesophageal Temperature and Hypotermia Risk Factors: An Observational Study. Turk J Anaesthesiol Reanim. 2021 Apr;49(2):100-106. doi: 10.5152/TJAR.2020.33. Epub 2020 May 18. PMID: 33997837; PMCID: PMC8098726. Sessler, D.I. Perianesthetic thermoregulation and heat balance in humans. FASEB J 7, 638–644 (1993). https://doi.org/10.1096/fasebj.7.8.8500693 Yi, J., Liang, H., Song, R. et al. Incidence of inadvertent intraoperative hypothermia and its risk factors in patients undergoing general anesthesia in Beijing: a prospective regional survey. PLoS One 10, e0136136 (2015). https://doi.org/10.1371/journal.pone.0136136 Campbell, G., Alderson, P., Smith, A.F., Warttig, S. Warming of intravenous and irrigation fluids for preventing inadvertent perioperative hypothermia. Cochrane Database Syst Rev 4, CD009891 (2015). https://doi.org/10.1002/14651858.CD009891.pub2 Sessler, D.I., Schroeder, M., Merrifield, B., Matsukawa, T., Cheng, C. Optimal duration and temperature of prewarming. Anesthesiology 82, 674–681 (1995). https://doi.org/10.1097/00000542-199503000-00008 Panagiotis, K., Maria, P., Argiri, P., Panagiotis, S. Is postanesthesia care unit length of stay increased in hypothermic patients? AORN J 81, 379–392 (2005). https://doi.org/10.1016/S0001-2092(06)60284-3 Additional Declarations No competing interests reported. Supplementary Files KeceliGraphicalAbstract300dpi.png Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 24 Apr, 2026 Reviews received at journal 18 Apr, 2026 Reviewers agreed at journal 18 Apr, 2026 Reviewers agreed at journal 17 Apr, 2026 Reviewers invited by journal 15 Apr, 2026 Editor invited by journal 23 Mar, 2026 Editor assigned by journal 19 Mar, 2026 Submission checks completed at journal 19 Mar, 2026 First submitted to journal 13 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9118190","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":628009881,"identity":"5193c406-f2d0-489c-ab00-6cadb511953c","order_by":0,"name":"Melike Ayça Keçeli","email":"","orcid":"","institution":"Acıbadem Maslak Hospital","correspondingAuthor":false,"prefix":"","firstName":"Melike","middleName":"Ayça","lastName":"Keçeli","suffix":""},{"id":628009882,"identity":"0dcf4975-af7f-4bcb-8928-b5b0806cc8bf","order_by":1,"name":"Özal Adıyeke","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA80lEQVRIiWNgGAWjYHACxgMMbBIMDDwMjA+APB4+YvTAtDAbgLSwEakFpBaskYGBoBZ+/sMPDvwos0js5zl8rPJrjp0MGwPzw0c38GiRbDhmcLDnnETizN62tNuy25KBDmMzNs7Bo8XgYIPBAd42icQN53nMbktuYwZq4WGTxqvlMPuHg3+BWvaf5/9WLLmtnggtx3gMDoNt4e1hY/y47TBhLZI9PAWHZc5JGM84c8xYmnHbcR42ZgJ+4ec/vvHhm7I62f6e5Icff26rtudnb374GJ8WGHBsABLMPCAmMxHKQcAeRDD+IFL1KBgFo2AUjCwAADhJSE8mgHkgAAAAAElFTkSuQmCC","orcid":"","institution":"Acıbadem Maslak Hospital","correspondingAuthor":true,"prefix":"","firstName":"Özal","middleName":"","lastName":"Adıyeke","suffix":""}],"badges":[],"createdAt":"2026-03-13 21:38:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9118190/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9118190/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107706888,"identity":"3b669b70-b8c7-4c00-8961-50ac366dacfb","added_by":"auto","created_at":"2026-04-24 09:18:59","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":382249,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eSTROBE-compliant participant flow diagram. \u003c/strong\u003e\u003c/em\u003eA total of 726 patients who underwent orthopedic surgery between February and May 2018 were screened. Of these, 639 did not meet the primary inclusion criteria (age \u0026lt;65 years, expected surgery duration \u0026lt;30 minutes, or anesthesia type other than general or regional). The remaining 87 patients were assessed for formal eligibility; 10 were excluded due to corticosteroid or immunosuppressive medication use (n=2), preoperative core temperature outside the 36–38°C range (n=3), or planned local anesthesia/refusal to provide written informed consent (n=5). All 87 enrolled patients completed intraoperative and PACU monitoring with full data collection (100% follow-up). No withdrawals or missing data occurred.\u003c/p\u003e","description":"","filename":"KeceliFigure1FlowDiagram300dpi.png","url":"https://assets-eu.researchsquare.com/files/rs-9118190/v1/33fc0ab2fd77a608db52f735.png"},{"id":107709194,"identity":"65c8f97a-ae34-420a-958e-ad8139338fc4","added_by":"auto","created_at":"2026-04-24 09:34:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":604412,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9118190/v1/7c390492-73ec-4264-bdd6-cffaec8800e9.pdf"},{"id":107619322,"identity":"4d6dd184-6d83-44e0-afb2-5325d52ea8d3","added_by":"auto","created_at":"2026-04-23 09:27:59","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":652872,"visible":true,"origin":"","legend":"","description":"","filename":"KeceliGraphicalAbstract300dpi.png","url":"https://assets-eu.researchsquare.com/files/rs-9118190/v1/1d5ec77b13def0a6c8b7cacf.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Perioperative hypothermia in geriatric orthopedic patients assessed by continuous zero-heat-flux monitoring: a prospective observational study","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith advances in medicine, technology, and preventive healthcare, global life expectancy has increased substantially, resulting in a growing proportion of elderly individuals presenting for surgical procedures. According to the World Health Organization (WHO), the geriatric age threshold is defined as 65 years. Globally, the number of people aged 65 years and older is projected to rise from 703\u0026nbsp;million in 2019 to 1.5\u0026nbsp;billion by 2050 \u0026mdash; representing a shift from 1 in 11 to 1 in 6 of the world's population - with the fastest growth occurring in low- and middle-income countries [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Advanced age is no longer considered an absolute contraindication for surgery, and increasingly major orthopedic procedures are being performed in this group [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eInadvertent perioperative hypothermia (IPH) \u0026mdash; defined as a core body temperature below 36\u0026deg;C occurring between one hour before anesthesia induction and 24 hours postoperatively \u0026mdash; is one of the most common yet preventable complications in surgical patients [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Its reported incidence varies widely, from 4% to as high as 90%, depending on the patient population, anesthetic technique, surgical setting, and monitoring method [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Both the American Society of Anesthesiologists (ASA) and the National Institute for Health and Care Excellence (NICE) recommend routine intraoperative temperature monitoring and active warming to prevent IPH [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. In Turkey, the Turkish Society of Anesthesiology and Reanimation (TARD) published its 'Prevention of Inadvertent Perioperative Hypothermia' guideline in 2013.\u003c/p\u003e \u003cp\u003eThermoregulation in humans is governed by the anterior hypothalamus, which maintains core temperature within a narrow range of 36.5\u0026ndash;37.3\u0026deg;C with circadian variation of only 0.5\u0026ndash;0.8\u0026deg;C. Anesthesia disrupts this regulation across all age groups; however, the effect is more pronounced in geriatric patients due to age-related blunting of vasoconstrictive and shivering responses, reduced metabolic rate, loss of subcutaneous fat, and sarcopenia [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The vasoconstrictive threshold decreases by approximately 1\u0026deg;C in individuals between 60 and 80 years of age.\u003c/p\u003e \u003cp\u003eThe clinical consequences of IPH are well established and include: increased incidence of surgical site infection, coagulopathy (platelet dysfunction, reduced clotting factor activity), cardiac morbidity (arrhythmias, myocardial ischemia), impaired drug metabolism (prolonged neuromuscular blockade, extended sedative effects), postoperative shivering, prolonged PACU stay, and increased healthcare costs [\u003cspan additionalcitationids=\"CR14 CR15 CR16\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWhile prior studies have examined perioperative hypothermia, a notable methodological limitation has been the use of intermittent, indirect, or invasive temperature measurement methods (axillary, tympanic, esophageal) that may fail to accurately reflect true core temperature. The zero-heat-flux (ZHF) method, employing the SpotOn\u0026trade; sensor applied to the frontotemporal region, creates an isothermal pathway that provides validated, continuous, non-invasive core temperature estimation comparable to esophageal measurement.\u003c/p\u003e \u003cp\u003eThe primary aims of this study were: (1) to determine the incidence of inadvertent perioperative hypothermia using continuous ZHF non-invasive core temperature monitoring in geriatric orthopedic patients; (2) to characterize the time course of intraoperative temperature decline; and (3) to identify modifiable and non-modifiable risk factors. To our knowledge, only a limited number of studies have used continuous ZHF monitoring for this specific patient population.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Study Design, Setting, and Ethics\u003c/h2\u003e \u003cp\u003eThis was a prospective, observational, single-blind study conducted at Istanbul Kanuni Sultan Suleyman Training and Research Hospital, University of Health Sciences, Istanbul, Turkey. Ethical approval was obtained from the Clinical Research Ethics Committee of Istanbul Bakirkoy Dr. Sadi Konuk Training and Research Hospital (Protocol No. 2018/292; Decision date: 29.01.2018). Written informed consent was obtained from all patients. The study was conducted in accordance with the Declaration of Helsinki. The anesthesia team and surgical staff were blinded to the study to allow unbiased observation of standard clinical practice.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Patient Selection\u003c/h2\u003e \u003cp\u003eBetween February and May 2018, a total of 726 patients who underwent orthopedic surgery at the study institution were screened for eligibility. Of these, 639 patients did not meet the inclusion criteria (age\u0026thinsp;\u0026lt;\u0026thinsp;65 years, expected surgery duration\u0026thinsp;\u0026lt;\u0026thinsp;30 minutes, or anesthesia type other than general or regional) and were not assessed further. Of the remaining 87 patients assessed for eligibility, 10 were excluded for the following reasons: use of corticosteroids or immunosuppressive medications (n\u0026thinsp;=\u0026thinsp;2), preoperative core temperature\u0026thinsp;\u0026lt;\u0026thinsp;36\u0026deg;C or \u0026gt;\u0026thinsp;38\u0026deg;C (n\u0026thinsp;=\u0026thinsp;3), and planned local anesthesia only or refusal to provide written informed consent (n\u0026thinsp;=\u0026thinsp;5). Accordingly, 87 patients who met all eligibility criteria were enrolled and completed the study (Fig.\u0026nbsp;1). Inclusion criteria: age\u0026thinsp;\u0026ge;\u0026thinsp;65 years; ASA physical status I\u0026ndash;IV; elective or emergency orthopedic procedure with expected duration\u0026thinsp;\u0026ge;\u0026thinsp;30 minutes; provision of written informed consent. Exclusion criteria: use of corticosteroids or immunosuppressive medications; preoperative core temperature\u0026thinsp;\u0026lt;\u0026thinsp;36\u0026deg;C or \u0026gt;\u0026thinsp;38\u0026deg;C; planned local anesthesia only; refusal to participate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Anesthesia Protocols\u003c/h2\u003e \u003cp\u003eAnesthetic technique was determined by the attending anesthesiologist based on patient condition and procedure type. General anesthesia (n\u0026thinsp;=\u0026thinsp;12, 13.8%): Preoxygenation for 3 minutes with 100% oxygen, then induction with propofol 2\u0026ndash;3 mg/kg IV (Propofol 1%, Fresenius Kabi), fentanyl 1 mcg/kg IV (Talinat 0.5 mg/10 ml, Vem), and rocuronium 0.6\u0026ndash;1.2 mg/kg IV (Muscuron 50 mg/5 ml, Kocak Farma). Maintenance: 2% sevoflurane in 50% O2/air mixture at 4 L/min total fresh gas flow via mechanical ventilation.\u003c/p\u003e \u003cp\u003eHypobaric spinal anesthesia (n\u0026thinsp;=\u0026thinsp;29, 33.3%): Sitting or lateral position; 25G Quincke needle (Egemen, Turkey) at L3\u0026ndash;L4 or L4\u0026ndash;L5 interspace; intrathecal injection of 17.5 mg marcaine (Marcaine 0.5%, AstraZeneca)\u0026thinsp;+\u0026thinsp;32 mcg fentanyl (Talinat)\u0026thinsp;+\u0026thinsp;1.3 ml sterile water for injection. Patient maintained in lateral decubitus (operative side uppermost) for 7 minutes.\u003c/p\u003e \u003cp\u003eHyperbaric spinal anesthesia (n\u0026thinsp;=\u0026thinsp;44, 50.6%): Same needle technique; intrathecal injection of 13 mg Heavy Marcaine (Marcaine Spinal Heavy 0.5%, AstraZeneca). Peripheral nerve block: n\u0026thinsp;=\u0026thinsp;2 (2.3%).\u003c/p\u003e \u003cp\u003ePremedication with midazolam 0.5 mg/kg IV (Zolamid 5 mg/5 ml, Defarma) was administered to 54 patients (62.1%). All IV fluids, blood products, and irrigation solutions were maintained at room temperature. All patients received passive warming (one 100% cotton blanket) in the premedication room and active warming (Bair Hugger forced-air warming system, 3M) intraoperatively per TARD guidelines until core temperature reached 37\u0026deg;C. Patients received supplemental oxygen by mask at 4 L/min throughout.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Temperature Monitoring and Data Collection\u003c/h2\u003e \u003cp\u003eCore body temperature was continuously monitored from the premedication room through PACU discharge using the SpotOn\u0026trade; Zero-Heat-Flux Temperature Monitoring System (3M, St. Paul, USA) applied to the frontotemporal region. This device provides non-invasive, continuous core temperature measurement validated against esophageal and pulmonary artery catheter measurements. Hypothermia was defined as core temperature\u0026thinsp;\u0026lt;\u0026thinsp;36\u0026deg;C at any measurement point.\u003c/p\u003e \u003cp\u003eA standardized data collection form was completed by the same study anesthesiologist throughout. Data recorded included: demographics (age, sex, BMI), ASA status, diagnosis, procedure type (elective/emergency), anesthesia type, premedication, anesthesia and surgery duration, IV fluid and blood product volumes with timing, and the operative minute at which temperature decrements of 0.5\u0026deg;C, 1.0\u0026deg;C, 1.5\u0026deg;C, 2.0\u0026deg;C, 2.5\u0026deg;C, and 3.0\u0026deg;C occurred. Room temperatures (premedication room, OR, PACU) were measured every 15 minutes using a TM898 digital thermometer (TT-TECHNIC, China). PACU discharge was based on modified Aldrete score\u0026thinsp;\u0026ge;\u0026thinsp;9.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Statistical Analysis\u003c/h2\u003e \u003cp\u003eData were analyzed using IBM SPSS Statistics v22.0. Categorical variables are presented as frequencies and percentages; continuous variables as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD). Between-group comparisons for categorical variables used Pearson chi-square and Fisher's exact tests. Continuous variables were compared by independent samples t-test. Correlations between continuous variables were assessed by Pearson correlation analysis. Odds ratios (OR) with 95% confidence intervals (CI) were calculated using standard 2\u0026times;2 contingency tables for primary binary risk factor comparisons. Statistical significance was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05. No a priori sample size calculation was performed as this was a prospective consecutive-enrollment observational study. Post-hoc power analysis confirmed that the enrolled sample of n\u0026thinsp;=\u0026thinsp;87 exceeded the minimum required sample size of n\u0026thinsp;=\u0026thinsp;63 (reference incidence: 43.9% [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] vs observed 51.7%; α\u0026thinsp;=\u0026thinsp;0.05; power\u0026thinsp;=\u0026thinsp;0.80). For the primary subgroup comparison of surgery duration (\u0026gt;\u0026thinsp;90 min vs\u0026thinsp;\u0026le;\u0026thinsp;90 min), achieved statistical power was 87.2%.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Demographics and Patient Characteristics\u003c/h2\u003e \u003cp\u003eOf the 726 patients screened during the study period, 87 were enrolled and all completed the study with full data collection (100% follow-up; Fig.\u0026nbsp;1). Ten patients were excluded prior to enrollment: 2 for corticosteroid or immunosuppressive medication use, 3 for preoperative core temperature outside the 36\u0026ndash;38\u0026deg;C range, and 5 for planned local anesthesia or refusal to consent. The 87 enrolled patients comprised 62 female (71.3%) and 25 male (28.7%). Age distribution: 38 patients (43.7%) were 65\u0026ndash;74 years, 36 (41.4%) were 75\u0026ndash;84 years, and 13 (14.9%) were \u0026ge;\u0026thinsp;85 years. BMI distribution: underweight (\u0026lt;\u0026thinsp;18.5 kg/m\u0026sup2;) n\u0026thinsp;=\u0026thinsp;2 (2.3%); normal weight (18.5\u0026ndash;24.99) n\u0026thinsp;=\u0026thinsp;27 (31.0%); overweight (25\u0026ndash;29.99) n\u0026thinsp;=\u0026thinsp;31 (35.6%); obese (\u0026ge;\u0026thinsp;30) n\u0026thinsp;=\u0026thinsp;27 (31.0%). ASA status: II in 29 (33.3%), III in 56 (64.4%), and IV in 2 (2.3%).\u003c/p\u003e \u003cp\u003eSurgical procedures: total knee arthroplasty (TKA) n\u0026thinsp;=\u0026thinsp;42 (48.3%), proximal femur nailing (PFN) n\u0026thinsp;=\u0026thinsp;19 (21.8%), partial hip arthroplasty n\u0026thinsp;=\u0026thinsp;12 (13.8%), total hip arthroplasty n\u0026thinsp;=\u0026thinsp;5 (5.7%), lower extremity surgery n\u0026thinsp;=\u0026thinsp;4 (4.6%), other orthopedic procedures n\u0026thinsp;=\u0026thinsp;4 (4.6%), upper extremity surgery n\u0026thinsp;=\u0026thinsp;1 (1.1%). Emergency procedures: n\u0026thinsp;=\u0026thinsp;5 (5.7%); elective: n\u0026thinsp;=\u0026thinsp;82 (94.3%). Premedication with midazolam was administered in 54 patients (62.1%).\u003c/p\u003e \u003cp\u003eAnesthesia duration distribution: 0\u0026ndash;60 minutes in 14 (16.1%), 61\u0026ndash;90 minutes in 25 (28.7%), 91\u0026ndash;120 minutes in 28 (32.2%), and \u0026gt;\u0026thinsp;120 minutes in 20 (23.0%). Mean surgery duration: 98.07\u0026thinsp;\u0026plusmn;\u0026thinsp;32.7 minutes. IV fluid volumes administered: 0\u0026ndash;1000 ml in 36 (41.4%), 1000\u0026ndash;1500 ml in 34 (39.1%), 1500\u0026ndash;2000 ml in 14 (16.1%), 2000\u0026ndash;2500 ml in 3 (3.4%).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePatient demographics and baseline characteristics (n\u0026thinsp;=\u0026thinsp;87)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e Variable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSex: Female / Male\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e62 (71.3%) / 25 (28.7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge: years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e74.3\u0026thinsp;\u0026plusmn;\u0026thinsp;7,5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge: 65\u0026ndash;74 years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e38 (43.7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge: 75\u0026ndash;84 years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36 (41.4%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge: \u0026ge;85 years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13 (14.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI: Normal (18.5\u0026ndash;24.99)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27 (31.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI: Overweight (25\u0026ndash;29.99)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31 (35.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI: Obese (\u0026ge;\u0026thinsp;30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27 (31.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eASA II / III / IV\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29 (33.3%) / 56 (64.4%) / 2 (2.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGeneral anesthesia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12 (13.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHypobaric spinal anesthesia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29 (33.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHyperbaric spinal anesthesia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e44 (50.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePeripheral nerve block\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 (2.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal knee arthroplasty\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e42 (48.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProximal femur nailing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19 (21.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean anesthesia duration\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e98.07\u0026thinsp;\u0026plusmn;\u0026thinsp;32.7 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePreop waiting time (premedication room)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16.78\u0026thinsp;\u0026plusmn;\u0026thinsp;11.89 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePACU recovery time\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.86\u0026thinsp;\u0026plusmn;\u0026thinsp;15.82 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eASA\u0026thinsp;=\u0026thinsp;American Society of Anesthesiologists; BMI\u0026thinsp;=\u0026thinsp;Body Mass Index; PACU\u0026thinsp;=\u0026thinsp;Post-Anesthesia Care Unit; SD\u0026thinsp;=\u0026thinsp;Standard Deviation.\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Environmental Temperatures\u003c/h2\u003e \u003cp\u003eMean premedication room temperature: 23.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.81\u0026deg;C. Mean operating room temperature: 19.61\u0026thinsp;\u0026plusmn;\u0026thinsp;1.38\u0026deg;C. Mean PACU temperature: 24.23\u0026thinsp;\u0026plusmn;\u0026thinsp;1.84\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Perioperative Core Temperature Profiles\u003c/h2\u003e \u003cp\u003eMean preoperative core temperature (premedication room): 36.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.50\u0026deg;C. Mean intraoperative core temperature: 36.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.65\u0026deg;C. Mean PACU core temperature: 35.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.83\u0026deg;C. Mean OR exit temperature: 35.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.84\u0026deg;C. Mean PACU exit temperature: 35.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.82\u0026deg;C.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCore temperatures and unit stay times by perioperative phase\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhase / Unit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMean Temperature\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMean Exit Temperature\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMean Stay Duration\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePremedication Room\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e36.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e36.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16.78\u0026thinsp;\u0026plusmn;\u0026thinsp;11.89 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOperating Room (intraoperative)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e36.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e35.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e98.07\u0026thinsp;\u0026plusmn;\u0026thinsp;32.70 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePACU (post-anesthesia care unit)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e35.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e35.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e27.86\u0026thinsp;\u0026plusmn;\u0026thinsp;15.82 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eSD\u0026thinsp;=\u0026thinsp;Standard Deviation; PACU\u0026thinsp;=\u0026thinsp;Post-Anesthesia Care Unit.\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Incidence of Perioperative Hypothermia\u003c/h2\u003e \u003cp\u003eIntraoperative hypothermia (core temperature\u0026thinsp;\u0026lt;\u0026thinsp;36\u0026deg;C during surgery) was detected in 45 patients (51.7%). At OR exit, 40 patients (46.0%) were hypothermic. Among patients who were hypothermic intraoperatively, 40 remained hypothermic at OR exit; 5 had recovered to normothermia. All 42 patients who were normothermic intraoperatively remained normothermic at OR exit.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eIncidence of intraoperative and postoperative hypothermia\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOutcome\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNormothermia n (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHypothermia n (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntraoperative (during surgery)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e42 (48.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e45 (51.7%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAt OR exit (postoperative)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e47 (54.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e40 (46.0%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eHypothermia defined as core temperature\u0026thinsp;\u0026lt;\u0026thinsp;36\u0026deg;C.\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Time Course of Intraoperative Temperature Decline\u003c/h2\u003e \u003cp\u003eContinuous ZHF monitoring permitted precise determination of the operative minute at which successive temperature decrements occurred. A 0.5\u0026deg;C drop occurred at a mean of 27.61\u0026thinsp;\u0026plusmn;\u0026thinsp;18.54 minutes; 1.0\u0026deg;C at 48.80\u0026thinsp;\u0026plusmn;\u0026thinsp;22.23 minutes; 1.5\u0026deg;C at 63.86\u0026thinsp;\u0026plusmn;\u0026thinsp;32.53 minutes; 2.0\u0026deg;C at 88.00\u0026thinsp;\u0026plusmn;\u0026thinsp;15.89 minutes; and 2.5\u0026deg;C at 91.12\u0026thinsp;\u0026plusmn;\u0026thinsp;35.03 minutes of surgery.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMean operative time at which successive core temperature decrements were reached\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTemperature Decrement\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMean Time\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (minutes)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5\u0026deg;C decrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e27.61\u0026thinsp;\u0026plusmn;\u0026thinsp;18.54\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.0\u0026deg;C decrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e48.80\u0026thinsp;\u0026plusmn;\u0026thinsp;22.23\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.5\u0026deg;C decrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e63.86\u0026thinsp;\u0026plusmn;\u0026thinsp;32.53\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.0\u0026deg;C decrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e88.00\u0026thinsp;\u0026plusmn;\u0026thinsp;15.89\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.5\u0026deg;C decrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e91.12\u0026thinsp;\u0026plusmn;\u0026thinsp;35.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eSD\u0026thinsp;=\u0026thinsp;Standard Deviation. Times represent the mean operative minute at which the specified decrement from baseline was first recorded.\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Risk Factors for Perioperative Hypothermia\u003c/h2\u003e \u003cp\u003eSurgery duration: Intraoperative hypothermia incidence was 20.0% for procedures\u0026thinsp;\u0026lt;\u0026thinsp;60 minutes, 37.9% for 61\u0026ndash;90 minutes, and 66.7% for \u0026gt;\u0026thinsp;90 minutes (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). At OR exit, hypothermia also increased significantly with procedure duration (p\u0026thinsp;=\u0026thinsp;0.003). A negative correlation of 45.9% was found between surgery duration and OR exit temperature (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Patients undergoing procedures lasting\u0026thinsp;\u0026gt;\u0026thinsp;90 minutes had significantly higher odds of intraoperative hypothermia compared to those with procedures\u0026thinsp;\u0026le;\u0026thinsp;90 minutes (OR 4.00, 95% CI 1.63\u0026ndash;9.80).\u003c/p\u003e \u003cp\u003ePreoperative body temperature: Higher preoperative temperature was significantly associated with lower intraoperative hypothermia incidence (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and lower postoperative hypothermia incidence (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eAnesthesia type: Patients under general anesthesia had significantly higher intraoperative hypothermia incidence compared to regional anesthesia patients (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Intraoperative hypothermia incidence under general anesthesia was 83.3% (10/12), versus 37.9% (11/29) for hypobaric spinal and 54.5% (24/44) for hyperbaric spinal anesthesia. General anesthesia was associated with over five-fold higher odds of intraoperative hypothermia compared to regional anesthesia (OR 5.43, 95% CI 1.11\u0026ndash;26.52). At OR exit, general anesthesia was also associated with significantly higher hypothermia (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). No statistically significant difference was found between hypobaric and hyperbaric spinal anesthesia in hypothermia incidence.\u003c/p\u003e \u003cp\u003eSurgical procedure: Patients undergoing total knee arthroplasty and procedures other than proximal femur nailing had significantly higher intraoperative hypothermia incidence (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Proximal femur nailing and lower extremity procedures were associated with significantly lower hypothermia incidence (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Postoperatively, proximal femur nailing was also associated with significantly lower hypothermia (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003eASA score: ASA II and ASA IV patients had significantly higher intraoperative hypothermia incidence compared to ASA III patients (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003eIV fluid volume: Significant association was found between intraoperative hypothermia and IV fluid volume administered (chi-square\u0026thinsp;=\u0026thinsp;9.934; p\u0026thinsp;=\u0026thinsp;0.019). Hypothermia incidence was 33.3% (12/36) in patients receiving 0\u0026ndash;1000 ml, 61.8% (21/34) in those receiving 1000\u0026ndash;1500 ml, 64.3% (9/14) in those receiving 1500\u0026ndash;2000 ml, and 100% (3/3) in those receiving 2000\u0026ndash;2500 ml. Patients receiving\u0026thinsp;\u0026gt;\u0026thinsp;1000 ml of IV fluid had significantly higher odds of intraoperative hypothermia compared to those receiving\u0026thinsp;\u0026le;\u0026thinsp;1000 ml (OR 3.67, 95% CI 1.49\u0026ndash;9.02).\u003c/p\u003e \u003cp\u003eSex: While no significant association was found between sex and intraoperative hypothermia, male patients had significantly higher hypothermia incidence at OR exit compared to female patients (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003ePACU recovery time: Patients who were hypothermic intraoperatively had significantly longer PACU recovery times compared to normothermic patients (p\u0026thinsp;=\u0026thinsp;0.021).\u003c/p\u003e \u003cp\u003eRoom temperature: No statistically significant correlation was found between premedication room temperature and intraoperative or OR-exit body temperature (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). Similarly, no significant correlation was found between mean OR temperature and OR-exit body temperature (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSignificant risk factors for intraoperative and postoperative hypothermia with odds ratios\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRisk Factor\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIntraop. Hypothermia Incidence\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOR (95% CI)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePostop. Hypothermia\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSurgery\u0026thinsp;\u0026gt;\u0026thinsp;90 min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e66.7% (32/48)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.00 (1.63\u0026ndash;9.80)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSignificant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.001 / p\u0026thinsp;=\u0026thinsp;0.003\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGeneral anesthesia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e83.3% (10/12)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.43 (1.11\u0026ndash;26.52)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSignificant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eASA II or IV status\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eElevated vs ASA III\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e\u0026mdash;*\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal knee arthroplasty\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eElevated vs other\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e\u0026mdash;*\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIV fluids\u0026thinsp;\u0026gt;\u0026thinsp;1000 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e62\u0026ndash;100% (33/51)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.67 (1.49\u0026ndash;9.02)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u0026thinsp;=\u0026thinsp;0.019\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHigh preop temperature\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProtective\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eProtective\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProximal femur nailing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReduced\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eReduced\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale sex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNS (intraop)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eElevated\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePACU recovery (hypothermic pts)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eProlonged\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u0026thinsp;=\u0026thinsp;0.021\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eOR\u0026thinsp;=\u0026thinsp;odds ratio; CI\u0026thinsp;=\u0026thinsp;confidence interval; NS\u0026thinsp;=\u0026thinsp;not statistically significant; IV\u0026thinsp;=\u0026thinsp;intravenous; ASA\u0026thinsp;=\u0026thinsp;American Society of Anesthesiologists. *OR not calculable due to multi-category comparison or insufficient cell counts.\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThis prospective observational study demonstrated that inadvertent perioperative hypothermia remains highly prevalent in geriatric orthopedic patients even when active warming protocols are in use, affecting 51.7% intraoperatively and 46.0% at OR exit. These findings are consistent with a large multicenter observational study by Alfonsi et al. [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], which reported a perioperative hypothermia prevalence of 53.5% on admission to the recovery room across 52 centers in France, despite active warming device use in 90.4% of patients \u0026mdash; reinforcing that protocol adherence rather than device availability is the key determinant of hypothermia prevention. The somewhat higher rate in our study likely reflects the older patient population (mean age 74.3 years), lower ambient OR temperature (19.6\u0026deg;C), and the inability to warm IV fluids.\u003c/p\u003e \u003cp\u003eA key methodological strength distinguishing this study is the use of continuous ZHF non-invasive core temperature monitoring. Unlike intermittent axillary or tympanic measurements \u0026mdash; which underestimate core temperature by 1\u0026ndash;4\u0026deg;C \u0026mdash; ZHF monitoring provides validated continuous data comparable to esophageal thermometry. This allowed precise characterization of the temperature decline time course: a 0.5\u0026deg;C drop at ~\u0026thinsp;28 minutes, 1.0\u0026deg;C at ~\u0026thinsp;49 minutes, 1.5\u0026deg;C at ~\u0026thinsp;64 minutes, 2.0\u0026deg;C at ~\u0026thinsp;88 minutes and 2.5\u0026deg;C at ~\u0026thinsp;91 minutes. These kinetics are consistent with the three-phase model of general anesthetic hypothermia described by Sessler [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]: rapid redistribution in Phase I (first 30\u0026ndash;45 min), linear decline in Phase II, and plateau in Phase III with peripheral vasoconstriction.\u003c/p\u003e \u003cp\u003eThe validity and clinical applicability of the ZHF method (SpotOn\u0026trade;, 3M) have been evaluated in several independent studies. Iden et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] compared SpotOn with sublingual and nasopharyngeal sensors in 120 gynecological and trauma surgery patients, concluding that ZHF offers sufficient accuracy for routine clinical use. Boisson et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] demonstrated in a prospective observational study that ZHF was a practical, non-invasive alternative to esophageal measurement across all perioperative phases, with the study becoming one of the most cited in ZHF validation literature. A multicenter study (ESOSPOT, NCT03820232) further confirmed the clinical acceptability of ZHF core temperature estimation against esophageal thermometry during major elective surgery [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. These validation data provide a strong methodological foundation for the findings reported in the present study.\u003c/p\u003e \u003cp\u003eTo date, only a limited number of prospective studies have specifically employed ZHF monitoring in orthopedic surgical populations. Munday et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] evaluated ZHF accuracy against esophageal thermometry in 30 patients undergoing upper and lower limb orthopedic surgery and observed that device bias was temperature-dependent \u0026mdash; a finding particularly relevant to the geriatric patient group where mild hypothermia predominates. Of direct relevance to the present study, Park et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] conducted a prospective comparison of ZHF (SpotOn), tympanic membrane, and bladder thermometry in patients aged\u0026thinsp;\u0026ge;\u0026thinsp;80 years undergoing lower extremity orthopedic surgery. Their critical finding was that hypothermia was detectable by both ZHF and bladder sensors at approximately 100\u0026ndash;110 minutes intraoperatively, whereas tympanic measurement failed to identify hypothermia in the same cohort \u0026mdash; underscoring the superiority of ZHF for hypothermia detection in elderly orthopedic patients and directly validating the monitoring approach used in the current study.\u003c/p\u003e \u003cp\u003eIn the Turkish literature, Duman et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] previously reported hypothermia incidence and risk factors in orthopedic surgery, albeit using conventional measurement methods. More recently, a study from Dokuz Eyl\u0026uuml;l University [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] employed SpotOn ZHF monitoring in major abdominal oncologic surgery, reporting a PACU hypothermia incidence of 38.1% and identifying absence of preoperative pre-warming and higher ASA score as leading risk factors \u0026mdash; findings broadly consistent with the present study. To the best of our knowledge, the current study remains one of the few to apply continuous ZHF monitoring specifically in a geriatric orthopedic cohort in Turkey, and the only study to provide detailed intraoperative temperature decline kinetics in this population.\u003c/p\u003e \u003cp\u003eThe significantly higher hypothermia incidence under general anesthesia (83.3%) versus regional anesthesia (37.9\u0026ndash;54.5%) in our cohort corroborates findings from Frisch et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], who reported a 43.9% hypothermia rate in total hip arthroplasty and 32.6% in total knee arthroplasty. General anesthetics raise the interthreshold range from 0.2\u0026deg;C to up to 4\u0026deg;C by suppressing hypothalamic regulation in a dose-dependent manner, inhibiting vasoconstriction and shivering \u0026mdash; the two primary heat-conserving responses. Regional anesthesia causes peripheral vasodilation and impairs thermoregulation below the block level, but preserves some central thermoregulatory capacity, resulting in a less severe but still significant hypothermic pattern [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe lack of significant difference between hypobaric and hyperbaric spinal anesthesia in our study supports the view that the extent of sympathetic blockade \u0026mdash; rather than the baricity of the local anesthetic \u0026mdash; determines thermoregulatory impairment during neuraxial anesthesia. Both techniques produced similar rates of hypothermia, a finding with direct clinical implications for practice.\u003c/p\u003e \u003cp\u003eThe strong positive correlation between IV fluid volume and hypothermia (p\u0026thinsp;=\u0026thinsp;0.019) is consistent with Yi et al. [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], who demonstrated that unwarmed fluid infusion of \u0026ge;\u0026thinsp;1000 ml significantly increases hypothermia incidence. The administration of room-temperature (19\u0026ndash;23\u0026deg;C) IV fluids, as was standard practice in our setting, represents a major and modifiable source of perioperative heat loss. Campbell et al. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] demonstrated in a Cochrane review of 25 trials (1250 patients) that warming IV fluids to 37\u0026ndash;41\u0026deg;C significantly attenuates core temperature decline compared to room-temperature administration.\u003c/p\u003e \u003cp\u003eThe association of total knee arthroplasty with higher hypothermia incidence compared to proximal femur nailing is likely attributable to multiple factors: longer typical procedure duration, more extensive tissue exposure, greater tourniquet-related blood redistribution, and higher IV fluid requirements in TKA. The protective effect of higher preoperative temperature reinforces the rationale for pre-warming in the premedication room, which reduces the core-to-peripheral gradient and thereby limits redistribution-induced heat loss in Phase I of anesthesia [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe finding that male sex was associated with higher postoperative hypothermia (OR-exit) but not intraoperative hypothermia is noteworthy and consistent with Panagiotis et al. [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Although women have higher body fat percentage (which provides better thermal insulation), they have lower muscle mass (reducing thermogenic capacity) and greater body surface area relative to volume \u0026mdash; factors that may offset each other intraoperatively but become relevant postoperatively as active warming is withdrawn.\u003c/p\u003e \u003cp\u003eHypothermic patients had significantly prolonged PACU recovery times (p\u0026thinsp;=\u0026thinsp;0.021), adding to the body of evidence linking IPH to increased healthcare resource utilization. Longer PACU stays increase nursing workload, delay ward bed availability, and contribute to healthcare costs \u0026mdash; effects that are amplified in high-volume orthopedic units serving geriatric patients.\u003c/p\u003e \u003cp\u003eA limitation of this study is its single-center, observational design without a control arm without warming. The inability to warm IV fluids due to institutional resource constraints \u0026mdash; which likely increased hypothermia rates \u0026mdash; and the lack of 24-hour postoperative temperature follow-up represent the main limitations. It should also be noted that while ZHF has been validated against esophageal thermometry across diverse surgical settings [\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], simultaneous comparative esophageal monitoring was not performed in the current study. Future multicenter randomized trials should evaluate the combined impact of IV fluid warming, preoperative forced-air pre-warming, and individualized warming protocols in geriatric orthopedic surgery, with continuous ZHF monitoring as the standard temperature assessment method.\u003c/p\u003e \u003cp\u003eRegarding generalisability, the findings of this study are most directly applicable to geriatric patients (\u0026ge;\u0026thinsp;65 years) undergoing lower extremity orthopedic surgery in tertiary care settings with similar resource and environmental conditions. The observed hypothermia rates may differ in institutions with higher baseline operating room temperatures, routine IV fluid warming, or more aggressive pre-warming protocols. Physiological and anthropometric differences across ethnic populations may also influence thermoregulatory responses; therefore, extrapolation to non-Turkish or non-geriatric populations should be made with caution. Nevertheless, the identified risk factors \u0026mdash; particularly anesthesia type, surgery duration, and IV fluid volume \u0026mdash; are consistent with findings from diverse international cohorts and are likely to be broadly generalizable across surgical settings.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThis prospective study confirms that perioperative hypothermia is a serious, prevalent, and clinically significant complication in geriatric patients undergoing orthopedic surgery, affecting more than half of patients intraoperatively and nearly half at OR exit despite active and passive warming measures. Key modifiable risk factors include general anesthesia, prolonged operative duration, unwarmed IV fluid volumes exceeding 1000 ml, and low preoperative body temperature. Continuous non-invasive ZHF core temperature monitoring enables early detection and timely intervention. Universal adherence to perioperative warming guidelines, routine warming of IV fluids, and interdisciplinary collaboration with the surgical team are strongly recommended to reduce the burden of this preventable complication in the geriatric orthopedic population.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics Approval:\u0026nbsp;\u003c/strong\u003eIstanbul Bakirkoy Dr. Sadi Konuk Training and Research Hospital Clinical Research Ethics Committee; Protocol No. 2018/292; Approval date 29.01.2018.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed Consent:\u0026nbsp;\u003c/strong\u003eWritten informed consent was obtained from all participants prior to enrollment.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u0026nbsp;\u003c/strong\u003eThis research received no external funding. No pharmaceutical or device company funding was received.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest:\u0026nbsp;\u003c/strong\u003eThe authors declare no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u0026nbsp;\u003c/strong\u003eMAK: study design, data collection, data analysis, manuscript drafting. ÖA: supervision, critical revision. All authors approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eUnited Nations Department of Economic and Social Affairs, Population Division. World Population Ageing 2019: Highlights. New York: United Nations; 2019. https://www.un.org/en/development/desa/population/publications/pdf/ageing/WorldPopulationAgeing2019-Highlights.pdf\u003c/li\u003e\n\u003cli\u003eMemtsoudis SG, Stundner O, Rasul R, Chiu YL, Sun X, Ramachandran SK, Fleischut P, Danninger T. Trends in the incidence and in-hospital outcomes of elective major orthopaedic surgery in patients eighty years of age and older in the United States from 2000 to 2009. J Bone Joint Surg Am. 2014;96(14):e120. doi: 10.2106/JBJS.M.01266. PMID: 25031373.\u003c/li\u003e\n\u003cli\u003eCan SO, Genc ST, Okten F. Anaesthesia management in geriatric orthopedic surgery patients: general or regional. Turk Klin J Anest Reanim. 2004;2:161-170.\u003c/li\u003e\n\u003cli\u003eTurkish Society of Anaesthesiology and Reanimation Practice Guideline for Prevention of Unintentional Perioperative Hypothermia. Turk J Anaesth Reanim. 2013;41:188\u0026ndash;190.\u003c/li\u003e\n\u003cli\u003eTorossian, A. Thermal management during anaesthesia and thermoregulation standards for the prevention of inadvertent perioperative hypothermia. Best Pract Res Clin Anaesthesiol. 2008;22(4):659-668.\u003c/li\u003e\n\u003cli\u003eLeslie, K., Sessler, D.I. Perioperative hypothermia in the high-risk surgical patient. Best Pract Res Clin Anaesthesiol 17, 485\u0026ndash;498 (2003). https://doi.org/10.1016/S1521-6896(03)00049-0\u003c/li\u003e\n\u003cli\u003eBurger, L., Fitzpatrick, J. Prevention of inadvertent perioperative hypothermia. Br J Nurs 18, 1114\u0026ndash;1119 (2009). https://doi.org/10.12968/bjon.2009.18.18.44553\u003c/li\u003e\n\u003cli\u003eTappen, R.M., Andre, S.P. Inadvertent hypothermia in elderly surgical patients. AORN J 63, 639\u0026ndash;644 (1996). https://doi.org/10.1016/S0001-2092(06)63431-3\u003c/li\u003e\n\u003cli\u003eAddendum to Clinical Guideline CG65, Inadvertent Perioperative Hypothermia. London: National Institute for Health and Care Excellence (NICE); 2016 Dec. PMID: 31825571.\u003c/li\u003e\n\u003cli\u003eAmerican Society of Anesthesiologists Committee on Standards and Practice Parameters. Standards for Basic Anesthetic Monitoring. Approved by the ASA House of Delegates, October 21, 1986; last amended October 20, 2010; effective July 1, 2011. Park Ridge (IL): ASA; 2011. Available at: https://www.asahq.org/standards-and-practice-parameters/standards-for-basic-anesthetic-monitoring\u003c/li\u003e\n\u003cli\u003eFrank, S.M., Fleisher, L.A., Breslow, M.J. et al. Perioperative maintenance of normothermia reduces the incidence of morbid cardiac events: a randomized clinical trial. JAMA 277, 1127\u0026ndash;1134 (1997). https://doi.org/10.1001/jama.1997.03540380041029\u003c/li\u003e\n\u003cli\u003eVan Someren, E.J. Thermoregulation and aging. Am J Physiol Regul Integr Comp Physiol 292, R99\u0026ndash;R102 (2007). https://doi.org/10.1152/ajpregu.00557.2006\u003c/li\u003e\n\u003cli\u003eSchmied, H., Reiter, A., Kurz, A., Sessler, D.I., Kozek, S. Mild hypothermia increases blood loss and transfusion requirements during total hip arthroplasty. Lancet 347, 289\u0026ndash;292 (1996). https://doi.org/10.1016/S0140-6736(96)90466-3\u003c/li\u003e\n\u003cli\u003eWinkler, M., Ak\u0026ccedil;a, O., Birkenberg, B. et al. Aggressive warming reduces blood loss during hip arthroplasty. Anesth Analg 91, 978\u0026ndash;984 (2000). https://doi.org/10.1097/00000539-200010000-00038\u003c/li\u003e\n\u003cli\u003eHeier, T., Caldwell, J.E., Sessler, D.I., Miller, R.D. Mild intraoperative hypothermia increases duration of action of vecuronium blockade. Anesthesiology 74, 815\u0026ndash;819 (1991). https://doi.org/10.1097/00000542-199105000-00007\u003c/li\u003e\n\u003cli\u003eKurz, A., Sessler, D.I., Lenhardt, R. Perioperative normothermia to reduce the incidence of surgical-wound infection. N Engl J Med 334, 1209\u0026ndash;1216 (1996). https://doi.org/10.1056/NEJM199605093341901\u003c/li\u003e\n\u003cli\u003eForbes, S.S., Eskicioglu, C., Nathens, A.B. et al. Evidence-based guidelines for prevention of perioperative hypothermia. J Am Coll Surg 209, 492\u0026ndash;503 (2009). https://doi.org/10.1016/j.jamcollsurg.2009.07.002\u003c/li\u003e\n\u003cli\u003eFrisch, N.B., Pepper, A.M., Rooney, E., Silverton, C. Intraoperative hypothermia in total hip and knee arthroplasty. Orthopedics 40, 56\u0026ndash;63 (2017). https://doi.org/10.3928/01477447-20161031-04\u003c/li\u003e\n\u003cli\u003eAlfonsi P, Bekka S, Aegerter P; SFAR Research Network investigators. Prevalence of hypothermia on admission to recovery room remains high despite a large use of forced-air warming devices: findings of a non-randomized observational multicenter and pragmatic study on perioperative hypothermia prevalence in France. PLoS One. 2019;14(12):e0226038. doi: 10.1371/journal.pone.0226038. PMID: 31869333; PMCID: PMC6927638.\u003c/li\u003e\n\u003cli\u003eSessler, D.I. Temperature monitoring and perioperative thermoregulation. Anesthesiology 109, 318\u0026ndash;338 (2008). https://doi.org/10.1097/ALN.0b013e31817f6d76\u003c/li\u003e\n\u003cli\u003eIden, T., Horn, E.P., Bein, B., B\u0026ouml;hm, R., Beese, J., H\u0026ouml;cker, J. Intraoperative temperature monitoring with zero heat flux technology (3M SpotOn sensor) in comparison with sublingual and nasopharyngeal temperature: a prospective observational study. Eur J Anaesthesiol 32, 387\u0026ndash;391 (2015). https://doi.org/10.1097/EJA.0000000000000232\u003c/li\u003e\n\u003cli\u003eBoisson M, Alaux A, Kerforne T, Mimoz O, Debaene B, Dahyot-Fizelier C, Frasca D. Intra-operative cutaneous temperature monitoring with zero-heat-flux technique (3M SpotOn) in comparison with oesophageal and arterial temperature: a prospective observational study. Eur J Anaesthesiol. 2018;35(11):825-830. doi:10.1097/EJA.0000000000000822.\u003c/li\u003e\n\u003cli\u003eEshraghi, Y., Nasr, V., Parra-Sanchez, I. et al. An evaluation of a zero-heat-flux cutaneous thermometer in cardiac surgical patients. Anesth Analg 119, 543\u0026ndash;549 (2014). https://doi.org/10.1213/ANE.0000000000000319\u003c/li\u003e\n\u003cli\u003eLiang H, Wang JY, Liang Y, Shao XF, Ding YL, Jia HQ. Agreement of zero-heat-flux thermometry with the oesophageal and tympanic core temperature measurement in patient receiving major surgery. J Clin Monit Comput. 2024 Feb;38(1):197-203. doi: 10.1007/s10877-023-01078-2. Epub 2023 Oct 4. PMID: 37792140; PMCID: PMC10879315.\u003c/li\u003e\n\u003cli\u003eMunday J, Higgins N, Jones L, Vagenas D, Van Zundert A, Keogh S. Zero-heat-flux and esophageal temperature monitoring in orthopedic surgery: an observational study. J Multidiscip Healthc. 2021;14:1819\u0026ndash;1827. doi: 10.2147/JMDH.S313310. PMID: 34285500; PMCID: PMC8286425.\u003c/li\u003e\n\u003cli\u003ePark C, Kim T, Oh S, Bang YS. Prospective comparative analysis of zero-heat-flux thermometer (SpotOn\u0026reg;) compared with tympanic thermometer and bladder thermometer in extremely aged patients undergoing lower extremity orthopedic surgery. Medicine (Baltimore). 2023 Oct 20;102(42):e35593. doi: 10.1097/MD.0000000000035593. PMID: 37861486; PMCID: PMC10589526.\u003c/li\u003e\n\u003cli\u003eDuman AY, Yılmaz E. Incidence of perioperative hypothermia in orthopaedic surgery and risk factors. Cukurova Med J. 2016;41(4):687-694.\u003c/li\u003e\n\u003cli\u003eAksu Erdost H, \u0026Ouml;zkardeşler S, Değirmenci AK, Dalak RM, Terzi C. Intraoperative Temperature Monitoring with Zero Heat Flux Technology (3M SpotOn Sensor) in Comparison with Tympanic and Oesophageal Temperature and Hypotermia Risk Factors: An Observational Study. Turk J Anaesthesiol Reanim. 2021 Apr;49(2):100-106. doi: 10.5152/TJAR.2020.33. Epub 2020 May 18. PMID: 33997837; PMCID: PMC8098726.\u003c/li\u003e\n\u003cli\u003eSessler, D.I. Perianesthetic thermoregulation and heat balance in humans. FASEB J 7, 638\u0026ndash;644 (1993). https://doi.org/10.1096/fasebj.7.8.8500693\u003c/li\u003e\n\u003cli\u003eYi, J., Liang, H., Song, R. et al. Incidence of inadvertent intraoperative hypothermia and its risk factors in patients undergoing general anesthesia in Beijing: a prospective regional survey. PLoS One 10, e0136136 (2015). https://doi.org/10.1371/journal.pone.0136136\u003c/li\u003e\n\u003cli\u003eCampbell, G., Alderson, P., Smith, A.F., Warttig, S. Warming of intravenous and irrigation fluids for preventing inadvertent perioperative hypothermia. Cochrane Database Syst Rev 4, CD009891 (2015). https://doi.org/10.1002/14651858.CD009891.pub2\u003c/li\u003e\n\u003cli\u003eSessler, D.I., Schroeder, M., Merrifield, B., Matsukawa, T., Cheng, C. Optimal duration and temperature of prewarming. Anesthesiology 82, 674\u0026ndash;681 (1995). https://doi.org/10.1097/00000542-199503000-00008\u003c/li\u003e\n\u003cli\u003ePanagiotis, K., Maria, P., Argiri, P., Panagiotis, S. Is postanesthesia care unit length of stay increased in hypothermic patients? AORN J 81, 379\u0026ndash;392 (2005). https://doi.org/10.1016/S0001-2092(06)60284-3\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-anesthesiology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bane","sideBox":"Learn more about [BMC Anesthesiology](http://bmcanesthesiol.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bane","title":"BMC Anesthesiology","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"geriatrics, hypothermia, thermoregulation, perioperative, temperature monitoring, zero-heat-flux, orthopedic surgery, anesthesia","lastPublishedDoi":"10.21203/rs.3.rs-9118190/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9118190/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground: \u003c/strong\u003eHypothermia, defined as core body temperature below 36°C, is a frequent complication in patients under general anesthesia and is closely associated with cardiovascular morbidity, perioperative hemorrhagic complications, impaired drug metabolism, and surgical site infection. Its impact is more pronounced in geriatric patients due to age-related physiological alterations including blunted thermoregulatory responses, sarcopenia, and reduced subcutaneous adipose tissue.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eObjective: \u003c/strong\u003eThis study aimed to determine the incidence of inadvertent perioperative hypothermia in geriatric patients (≥65 years) undergoing orthopedic surgery under general or regional anesthesia, using continuous non-invasive core temperature monitoring via the zero-heat-flux (ZHF) method, and to identify associated risk factors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods: \u003c/strong\u003eA prospective observational study was conducted between February and May 2018 at Istanbul Kanuni Sultan Suleyman Research and Training Hospital following ethics committee approval (Protocol No. 2018/292). A total of 87 patients aged ≥65 years undergoing orthopedic surgery with an expected duration ≥30 minutes were enrolled. Core temperature was monitored continuously from the premedication room through PACU discharge using the SpotOn™ Zero-Heat-Flux sensor (3M, St. Paul, USA). Active warming (Bair Hugger forced-air system, 3M) was applied to all patients. Statistical analyses included chi-square, Fisher's exact test, t-test, Pearson correlation, and SPSS v22.0 (significance: p\u0026lt;0.05).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults: \u003c/strong\u003eOf the 87 patients (62 female, 25 male; mean age 74.3 ± 7,5 years), intraoperative hypothermia was detected in 51.7% (n=45; 95% CI 41.2–62.2%) and postoperative hypothermia in 46.0% (n=40; 95% CI 35.5–56.5%). Mean preoperative temperature was 36.84 ± 0.50°C; mean intraoperative temperature 36.29 ± 0.65°C; mean PACU temperature 35.91 ± 0.83°C. Temperature drops of 0.5°C, 1°C, 1.5°C, 2°C, and 2.5°C occurred at a mean of 27.6, 48.8, 63.9, 88.0, and 91.1 minutes, respectively. Significant risk factors for intraoperative hypothermia included: prolonged surgery (\u0026gt;90 min, 66.7%; OR 4.00, 95% CI 1.63–9.80; p\u0026lt;0.001), general anesthesia (OR 5.43, 95% CI 1.11–26.52; p\u0026lt;0.05), IV fluid volume \u0026gt;1000 ml (OR 3.67, 95% CI 1.49–9.02; p=0.019), ASA II and IV status (p\u0026lt;0.05), and total knee arthroplasty (p\u0026lt;0.05). Higher preoperative body temperature was protective (p\u0026lt;0.001). Hypothermic patients had significantly longer PACU recovery times (p=0.021).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion: \u003c/strong\u003ePerioperative hypothermia is highly prevalent in geriatric orthopedic patients even when active warming protocols are in use. General anesthesia, prolonged surgery, high ASA score, large fluid volumes, and low preoperative body temperature are key risk factors. Continuous non-invasive ZHF core temperature monitoring enables early detection. Strict adherence to warming protocols, use of prewarmed IV fluids, and interdisciplinary collaboration are essential to reduce hypothermia and its associated morbidity in this vulnerable population.\u003c/p\u003e","manuscriptTitle":"Perioperative hypothermia in geriatric orthopedic patients assessed by continuous zero-heat-flux monitoring: a prospective observational study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-23 09:27:55","doi":"10.21203/rs.3.rs-9118190/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-04-24T18:45:40+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-18T16:03:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"319594286028898095812387358388219984177","date":"2026-04-18T14:54:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"256622275316666732413497932971856662846","date":"2026-04-17T13:08:43+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-15T12:36:35+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-03-23T08:02:27+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-19T09:36:59+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-19T09:36:10+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Anesthesiology","date":"2026-03-13T21:23:51+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-anesthesiology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bane","sideBox":"Learn more about [BMC Anesthesiology](http://bmcanesthesiol.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bane","title":"BMC Anesthesiology","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4212197e-29d2-4ca7-9a89-e9e192b3912f","owner":[],"postedDate":"April 23rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-23T09:27:55+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-23 09:27:55","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9118190","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9118190","identity":"rs-9118190","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}