Effects of Different Fresh Gas Flow Rates on Body Temperature and Postoperative Nausea and Vomiting in Morbidly Obese Patients Undergoing Laparoscopic Sleeve Gastrectomy

Effects of Different Fresh Gas Flow Rates on Body Temperature and Postoperative Nausea and Vomiting in Morbidly Obese Patients Undergoing Laparoscopic Sleeve Gastrectomy | 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 Effects of Different Fresh Gas Flow Rates on Body Temperature and Postoperative Nausea and Vomiting in Morbidly Obese Patients Undergoing Laparoscopic Sleeve Gastrectomy Muhammed Başpınar, Duygu Tuncer Sel, Ahmet Aksu, Gülsüm Altuntaş, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8671925/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Introduction: Inadvertent perioperative hypothermia and postoperative nausea and vomiting (PONV) remain common after metabolic and bariatric surgery (MBS). Fresh gas flow (FGF) may influence heat and humidity conservation within the breathing circuit and thereby affect perioperative temperature and PONV. Methods: In this single-center, randomized, prospective trial, 161 adults with obesity class III (BMI > 40 kg/m²) scheduled for laparoscopic sleeve gastrectomy were allocated to normal-flow (2.0 L/min; n=53), low-flow (1.0 L/min; n=55), or minimal-flow anesthesia (0.5 L/min; n=53). Esophageal and tympanic temperatures and hemodynamic variables were recorded every 10 minutes intraoperatively. PONV was assessed in the post-anesthesia care unit (PACU) and at 6, 12, and 24 hours postoperatively. Results: Baseline characteristics were comparable among groups. From the 20th minute onward, esophageal and tympanic temperatures differed between groups (p<0.001), with higher temperatures in the minimal-flow group. The proportion of patients without PONV in the PACU and at 6, 12, and 24 hours was highest with minimal-flow anesthesia and lowest with normal-flow anesthesia (p0.05). Conclusion: Minimal-flow anesthesia (0.5 L/min) better preserved perioperative temperature and was associated with lower PONV after laparoscopic sleeve gastrectomy, without compromising hemodynamic stability. laparoscopic sleeve gastrectomy low-flow anesthesia minimal-flow anesthesia hypothermia postoperative nausea and vomiting Figures Figure 1 Figure 2 Figure 3 Figure 4 Key Points • Minimal-flow (0.5 L/min) maintained higher core temperature after sleeve gastrectomy. • Minimal-flow anesthesia was associated with the lowest PONV through 24 hours. • Hemodynamics and SpO₂ were similar across 2.0, 1.0, and 0.5 L/min FGF strategies. Introduction Despite the availability of various therapeutic options for obesity, surgical treatments have gained prominence in recent years. Among surgical approaches, laparoscopic sleeve gastrectomy (LSG) is being performed increasingly often and has become established as a safe and effective procedure [ 1 ]. Nevertheless, patients may experience multiple adverse events in the perioperative period, related to both surgery and anesthesia. Inadvertent perioperative hypothermia, reported in more than half of surgical patients, can lead to numerous unfavorable outcomes, including sympathetic activation-related cardiac events, increased incidence of postoperative nausea and vomiting (PONV), surgical site infections, prolonged hospital stay, and coagulopathy [ 2 ]. Because individuals with obesity have increased adipose tissue that reduces cutaneous heat loss and generally higher leptin levels, hypothermia might be expected to occur less frequently than in non-obese patients. However, even mild hypothermia may increase perioperative risk; therefore, monitoring and prevention remain clinically important [ 3 ]. Although various strategies have been developed to prevent or reduce perioperative heat loss, methods that conserve heat and humidity within the airway have been reported among the most effective approaches [ 4 ]. Low fresh gas flow (FGF) anesthesia and prolonged operative duration have been associated with intraoperative hypothermia [ 5 ]. Low-flow anesthesia has been shown to reduce airway heat and moisture loss, optimize intraoperative core temperature, and attenuate the degree of induced hypothermia [ 6 ]. One of the most distressing complications for surgical patients is PONV. In addition to prolonging hospital stay and increasing healthcare costs, PONV may contribute to serious adverse events. PONV is known to be more common in morbidly obese patients [ 7 ]. Moreover, PONV has been reported in approximately 80% of bariatric procedures, and LSG appears to have the highest PONV incidence among standard bariatric operations [ 8 ]. Even when prophylaxis recommendations based on the Apfel risk score are applied, up to 82% of patients undergoing metabolic and bariatric surgery may still experience PONV in the post-anesthesia care unit (PACU) [ 9 ]. The present study aimed to investigate the effects of different fresh gas flow rates on body temperature and PONV in patients undergoing laparoscopic sleeve gastrectomy. Materials and Methods Study design and setting This single-center, randomized, prospective study was conducted in the operating rooms of Fırat University Hospital between 01/10/2022 and 01/05/2023. A total of 231 patients scheduled for laparoscopic sleeve gastrectomy due to morbid obesity were assessed. After exclusions and refusals, 161 patients were randomized into three groups according to the planned fresh gas flow (FGF) rate and completed the study (Fig. 1 ). Ethics approval and informed consent Ethics approval was obtained from the Fırat University Faculty of Medicine Clinical Research Ethics Committee (07/09/2022, No. 222335). All eligible participants were informed about the study and provided written informed consent. Participants: inclusion and exclusion criteria Patients aged 18–65 years with American Society of Anesthesiologists (ASA) physical status III and body mass index (BMI) > 40 kg/m², undergoing laparoscopic sleeve gastrectomy and consenting to participate were included. Patients undergoing bariatric procedures other than sleeve gastrectomy; those younger than 18 years; with arrhythmia; left ventricular ejection fraction < 30%; hepatic or renal dysfunction; a history of PONV in previous surgeries; a history of motion sickness; current active smoking; or ASA physical status IV were excluded. Randomization and group allocation Using a sealed-envelope method, 161 patients were randomized into three groups according to the planned FGF rate: • Normal-flow anesthesia (NFA) group (n = 53): FGF 2 L/min • Low-flow anesthesia (LFA) group (n = 55): FGF 1 L/min • Minimal-flow anesthesia (MFA) group (n = 53): FGF 0.5 L/min Anesthesia management and monitoring After 3 minutes of preoxygenation with 100% oxygen at 10 L/min, anesthesia was induced using propofol 2–3 mg/kg based on total body weight (Propofol® 1%, Fresenius, Germany), remifentanil 1 µg/kg based on ideal body weight (Ultiva®, GSK, USA), and rocuronium bromide 0.6–0.8 mg/kg (Esmeron®, MSD, Germany). After adequate anesthetic depth was achieved, endotracheal intubation was performed. Esophageal and tympanic temperature probes were placed and temperature measurements were recorded. Maintenance anesthesia consisted of sevoflurane (Sevorane®, 100% liquid, AbbVie, UK) and a remifentanil infusion based on ideal body weight at 0.05–0.2 µg/kg/min. Additional rocuronium was administered as needed. Patients were ventilated to maintain an end-tidal CO₂ of 35–45 mmHg, with a tidal volume of 8 mL/kg ideal body weight and an inspiratory-to-expiratory ratio of 1:2 to maintain normocapnia. At the end of surgery, residual neuromuscular blockade was reversed using sugammadex 2 mg/kg intravenously (Bridion®, MSD, Netherlands) based on ideal body weight. For PONV prophylaxis, metoclopramide 20 mg (Metpamid®, Safir Farma, Istanbul) was administered. An anesthesia workstation capable of low and minimal flow anesthesia (Maquet Flow-i C20®, Solna, Sweden) was used. Before induction, a self-test including a breathing circuit leak test was performed, and soda lime was checked to ensure adequate function. All operations were performed by the same surgical team, and intra-abdominal pressure was maintained below 15 mmHg. Operating room temperature was maintained at 22°C throughout surgery. Fresh gas flow protocol In the NFA group, after achieving the target minimum alveolar concentration (MAC), FGF was set to 2 L/min. In the LFA group, after achieving target MAC, FGF was set to 1 L/min. To maintain FiO₂ above 35%, oxygen concentration was increased as required. Sevoflurane concentration was adjusted to maintain target MAC. In the MFA group, after achieving target MAC, FGF was set to 0.5 L/min. To maintain FiO₂ above 35%, oxygen concentration was increased as required. Sevoflurane concentration was adjusted to maintain target MAC. Sample size calculation Before the study, sample size calculation was performed using G*Power (version 3.1.9.2), informed by the literature and expert opinion. With a 95% confidence level and 95% power, at least 52 patients per group were required (total minimum n = 156). Data collection After positioning on the operating table, heart rate, end-tidal CO₂, SpO₂, mean arterial pressure (MAP), MAC, inspired CO₂ (FiCO₂), inspired oxygen fraction (FiO₂), and tympanic and esophageal temperatures were recorded every 10 minutes. MAP was targeted to remain above 65 mmHg; vasopressor support was provided when MAP fell below 65 mmHg. After arrival in the PACU, patients were monitored and heart rate, SpO₂, MAP, tympanic temperature, and PONV score (1: no nausea/vomiting; 2: nausea; 3: retching; 4: vomiting) were recorded at admission and at 10, 20, and 30 minutes. Patients with a Modified Aldrete Score of 9 or higher were discharged from the PACU. Postoperative heart rate, SpO₂, MAP, tympanic temperature, and PONV score were recorded at 6, 12, and 24 hours postoperatively. Outcomes The primary outcomes were changes in body temperature and PONV across the three FGF groups, evaluated both within and between groups. Secondary outcomes were changes in hemodynamic parameters (heart rate, MAP, and SpO₂) across the three FGF groups, evaluated both within and between groups. Statistical analysis Analyses were performed using SPSS version 22 (SPSS Inc., Chicago, IL, USA). Categorical variables are presented as n (%), and continuous variables as mean ± standard deviation. Between-group comparisons of categorical variables were conducted using the chi-square (Pearson) test. Normality was assessed using the Kolmogorov-Smirnov test. For comparisons among more than two groups, the Kruskal-Wallis test was used. Statistical significance was set at p 0.05) (Table 1 ). Table 1 Comparison of demographic characteristics and anthropometric measurements among the groups. Variable NFA (n = 53) LFA (n = 55) MFA (n = 53) p* Age (years) 39.2 ± 12.9 35.7 ± 11.9 37.1 ± 9.2 0.335 BMI (kg/m²) 44.6 ± 6.7 45.9 ± 5.1 43.8 ± 6.9 0.573 Sex (female/male) 27/26 30/25 28/25 0.297 * p values were calculated using Kruskal-Wallis test for continuous variables and chi-square test for categorical variables. Hemodynamic parameters Perioperative SpO₂, heart rate, and MAP values did not differ significantly between groups (p > 0.05). Temperature measurements Esophageal and tympanic temperature measurements differed significantly between groups starting from the 20th minute (p < 0.001). This difference was mainly attributable to higher temperature values in the minimal-flow group (Figs. 2 and 3 ). Postoperative nausea and vomiting PONV incidence in the PACU and at postoperative 6, 12, and 24 hours was lowest in the minimal-flow group and highest in the normal-flow group. This difference was statistically significant (p < 0.05) (Fig. 4 ). Discussion With the rapid global increase in the number of individuals with morbid obesity, anesthesiologists increasingly encounter morbidly obese patients in surgical practice. Every surgical intervention carries multiple risks related to both surgery and anesthesia. One such risk, inadvertent perioperative hypothermia, is defined as a decrease in body temperature below 36°C from the preoperative period through the postoperative period (the first 24 hours after anesthesia). The reported incidence ranges from approximately 40% to 70% [ 10 – 11 ]. Under normal conditions, core temperature is regulated by the hypothalamus. When core temperature is around 37°C, deviations as small as 0.2°C activate the thermoregulatory system, adjusting heat production and distribution to maintain thermal homeostasis. Intravenous and inhalational anesthetics inhibit hypothalamic control and widen the interthreshold range from approximately 0.2°C up to 4°C, delaying thermoregulatory responses. In addition, immobility in a cool operating room environment, inhalation of cold gases, and heat losses from body cavities contribute to temperature decline. Thermal redistribution from the core to the periphery within the first hour of general anesthesia is a major driver of the initial rapid decrease in core temperature [ 12 ]. Individuals with obesity have an increased layer of subcutaneous adipose tissue that acts as an insulating barrier due to its low thermal conductivity, thereby reducing conductive heat loss through the skin. Moreover, these patients may exhibit higher vasoconstriction thresholds, leading to earlier peripheral vasoconstriction and a more limited redistribution of heat from core to periphery. The magnitude of intraoperative core temperature decrease and redistribution hypothermia has been shown to be inversely related to body fat percentage and body surface area [ 13 ]. Studies comparing obese and non-obese patients have reported significantly higher intraoperative and postoperative temperatures in obese patients [ 14 ]. However, it should also be considered that obese patients may be prone to substantial heat loss after prolonged exposure to hypothermia due to relatively lower muscle mass and a higher surface area-to-mass ratio [ 15 ]. Inadvertent perioperative hypothermia is clinically important because of its associated complications, including surgical site infection, postoperative ischemic myocardial events, increased intraoperative blood loss, increased PONV (and consequently a potential increase in anastomotic leak and rupture risk), and delayed postoperative recovery. Therefore, achieving and maintaining normothermia in the perioperative period is important for optimal surgical outcomes as well as patient safety and satisfaction [ 16 ]. Traditional approaches to prevent hypothermia during general anesthesia include warming intravenous fluids, using heat-and-moisture exchangers, forced-air warming blankets or radiant warmers, and increasing operating room temperature; low-flow anesthesia may also be considered [ 17 ]. In a prior study comparing high-, low-, and minimal-flow anesthesia, temperature distributions differed significantly between groups after the 20th minute. Body temperature values were similar in the low-flow and minimal-flow groups and higher than those in the high-flow group [ 18 ]. In the present study of morbidly obese patients undergoing LSG, our findings were consistent with the literature and indicated that minimal-flow anesthesia better preserved intraoperative body temperature. Low- and minimal-flow anesthesia techniques have been increasingly adopted in recent years because of potential environmental benefits, cost savings, and contributions to more physiologic respiratory conditions. These techniques are also known to better preserve the temperature and humidity of inspired gases, promoting thermal stability. Concerns persist regarding potential hemodynamic instability; however, the literature suggests that these techniques do not compromise hemodynamic stability and can be used safely [ 19 ]. Similarly, in our study, hemodynamic stability was maintained and no significant between-group differences were observed. PONV is one of the most common complications after general anesthesia and is associated with multiple pathophysiologic mechanisms [ 20 – 23 ]. In metabolic and bariatric surgery, PONV is a frequent complication. In a comprehensive review published in 2025, Jumaev et al. reported a high incidence of PONV after sleeve gastrectomy and highlighted multiple contributing factors [ 24 ]. Likewise, in a retrospective cohort study, Tan et al. showed that PONV incidence varies with anesthetic technique, body temperature, and hydration status [ 25 ]. The mechanisms of PONV are complex and influenced by numerous risk factors [ 26 ]. A decline in intraoperative body temperature has been associated with prolonged extubation time, longer stay in intensive care units, and increased postoperative complications [ 22 ]. In a pediatric study, nausea incidence at postoperative 6 hours was significantly higher in children with body temperature below 36°C compared with those above 36°C [ 27 ]. In our study, the higher temperature profile in the minimal-flow group may have contributed to the lower PONV incidence. The impact of thermoregulation on neuroendocrine pathways related to nausea perception may help explain these findings [ 23 , 28 ]. Preventing hypothermia by maintaining thermal balance has been suggested to reduce complications such as PONV. In a study of morbidly obese patients, maintaining core temperature above 36°C with forced-air warming significantly reduced PONV incidence [ 29 ]. Other studies likewise report lower nausea and vomiting rates in groups with better temperature preservation [ 27 , 30 – 32 ]. These findings support the physiologic rationale for the lower PONV rates observed in our minimal-flow group. This study has several limitations. It was conducted at a single center and included patients treated within one institution, which may limit generalizability. The cohort was restricted to morbidly obese patients undergoing laparoscopic sleeve gastrectomy, and no comparisons were made with other surgical procedures. The semi-quantitative PONV scoring system may be subject to subjective interpretation. Individual factors that could influence thermoregulatory responses (e.g., menopausal status, endocrine disorders) were not standardized. Finally, follow-up was limited to 24 hours, and longer-term outcomes could not be assessed. Conclusion In conclusion, low- and minimal-flow anesthesia, when applied with close patient monitoring and modern anesthesia workstations, may be preferable because of potential environmental benefits, cost reduction, provision of more physiologic respiratory conditions, and attenuation of intraoperative hypothermia. Based on our findings, low- and minimal-flow anesthesia can be used safely in patients undergoing LSG, as these techniques maintained hemodynamic stability, better preserved body temperature, and reduced PONV incidence. Nevertheless, further studies with larger patient series are warranted. Declarations Funding: This study received no external funding. Conflict of Interest: The authors declare that they have no conflict of interest. Ethical Approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Ethics committee approval was obtained from the local Clinical Research Ethics Committee (approval details blinded for review). Informed Consent: Informed consent was obtained from all individual participants included in the study. Data Availability: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request. References Masry MAME, Fiky MAME. Long-Term Outcome of Laparoscopic Sleeve Gastrectomy (LSG) on Weight Loss in Patients with Obesity: a 5-Year and 11-Year Follow-Up Study. Obes Surg. 2023;33(10):3147–54. 10.1007/s11695-023-06781-2 . Epub 2023 Aug 22. Collins S, Budds M, Raines C, Hooper V. 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Obes Surg. 2018;28(7):1955–9. Ji J, Gu X, Xiao C. Comparison of perioperative active or routine temperature management on postoperative quality of recovery in PACU in patients undergoing thoracoscopic lobectomy: a randomized controlled study. Int J Gen Med. 2022;15:429–36. Liang D, Shan Y, Wang L. The effect of prophylactic rewarming on postoperative nausea and vomiting among patients undergoing laparoscopic hysterectomy: a prospective randomized clinical study. Sao Paulo Med J. 2020;138(5):414–21. Liu M, Qi L. The related factors and countermeasures of hypothermia in patients during the anesthesia recovery period. Am J Transl Res. 2021;13(4):3459–65. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. 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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-8671925","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":581908425,"identity":"ab3704b9-e281-4779-81e9-0ed49da0689c","order_by":0,"name":"Muhammed 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Hastanesi","correspondingAuthor":false,"prefix":"","firstName":"Duygu","middleName":"Tuncer","lastName":"Sel","suffix":""},{"id":581908427,"identity":"b8e8360a-a512-4346-a8bb-a2d7cdd0b9e1","order_by":2,"name":"Ahmet Aksu","email":"","orcid":"","institution":"Fırat Üniversitesi Hastanesi","correspondingAuthor":false,"prefix":"","firstName":"Ahmet","middleName":"","lastName":"Aksu","suffix":""},{"id":581908428,"identity":"14cec409-d30d-49a0-9c8b-3c6e15d4c2a3","order_by":3,"name":"Gülsüm Altuntaş","email":"","orcid":"","institution":"Fırat Üniversitesi Hastanesi","correspondingAuthor":false,"prefix":"","firstName":"Gülsüm","middleName":"","lastName":"Altuntaş","suffix":""},{"id":581908429,"identity":"c6420333-04fe-4132-8805-6793628962d4","order_by":4,"name":"İsmail Demirel","email":"","orcid":"","institution":"Fırat Üniversitesi Hastanesi","correspondingAuthor":false,"prefix":"","firstName":"İsmail","middleName":"","lastName":"Demirel","suffix":""}],"badges":[],"createdAt":"2026-01-22 16:38:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8671925/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8671925/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":101460089,"identity":"41b0c31b-f992-4af9-ac67-450e7b708586","added_by":"auto","created_at":"2026-01-30 01:37:28","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":141701,"visible":true,"origin":"","legend":"\u003cp\u003eStudy flow diagram.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8671925/v1/e438d6cd14bcd6670aefc9b1.png"},{"id":101460094,"identity":"0332693a-0145-404e-9bf4-6ae1bd254c30","added_by":"auto","created_at":"2026-01-30 01:37:29","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":92054,"visible":true,"origin":"","legend":"\u003cp\u003eChange in esophageal temperature over time among the NFA, LFA, and MFA groups\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8671925/v1/6c8a6723809ccc3e0b62d031.png"},{"id":101460092,"identity":"8fe87856-50cb-4214-b03d-c4acc374465f","added_by":"auto","created_at":"2026-01-30 01:37:28","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":95000,"visible":true,"origin":"","legend":"\u003cp\u003eChange in tympanic temperature over time among the NFA, LFA, and MFA groups\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8671925/v1/2d2543bca52be77c1d3128ef.png"},{"id":101460090,"identity":"6d795d66-52b4-4dc1-951b-cda41485948e","added_by":"auto","created_at":"2026-01-30 01:37:28","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":426515,"visible":true,"origin":"","legend":"\u003cp\u003eIncidence of PONV-free patients over time among the NFA, LFA, and MFA groups\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8671925/v1/dfe46e2bd4e9e8ce4a4580bd.png"},{"id":108977557,"identity":"cbb9a2cc-ef04-4ed6-9660-51e0045167ed","added_by":"auto","created_at":"2026-05-11 11:32:05","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":944022,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8671925/v1/bbbab1b5-51cf-4777-8e4a-76ab20a3b5b5.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of Different Fresh Gas Flow Rates on Body Temperature and Postoperative Nausea and Vomiting in Morbidly Obese Patients Undergoing Laparoscopic Sleeve Gastrectomy","fulltext":[{"header":"Key Points","content":"\u003cp\u003e\u0026bull; Minimal-flow (0.5 L/min) maintained higher core temperature after sleeve gastrectomy.\u003c/p\u003e\u003cp\u003e\u0026bull; Minimal-flow anesthesia was associated with the lowest PONV through 24 hours.\u003c/p\u003e\u003cp\u003e\u0026bull; Hemodynamics and SpO₂ were similar across 2.0, 1.0, and 0.5 L/min FGF strategies.\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eDespite the availability of various therapeutic options for obesity, surgical treatments have gained prominence in recent years. Among surgical approaches, laparoscopic sleeve gastrectomy (LSG) is being performed increasingly often and has become established as a safe and effective procedure [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Nevertheless, patients may experience multiple adverse events in the perioperative period, related to both surgery and anesthesia.\u003c/p\u003e \u003cp\u003eInadvertent perioperative hypothermia, reported in more than half of surgical patients, can lead to numerous unfavorable outcomes, including sympathetic activation-related cardiac events, increased incidence of postoperative nausea and vomiting (PONV), surgical site infections, prolonged hospital stay, and coagulopathy [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Because individuals with obesity have increased adipose tissue that reduces cutaneous heat loss and generally higher leptin levels, hypothermia might be expected to occur less frequently than in non-obese patients. However, even mild hypothermia may increase perioperative risk; therefore, monitoring and prevention remain clinically important [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAlthough various strategies have been developed to prevent or reduce perioperative heat loss, methods that conserve heat and humidity within the airway have been reported among the most effective approaches [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Low fresh gas flow (FGF) anesthesia and prolonged operative duration have been associated with intraoperative hypothermia [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Low-flow anesthesia has been shown to reduce airway heat and moisture loss, optimize intraoperative core temperature, and attenuate the degree of induced hypothermia [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOne of the most distressing complications for surgical patients is PONV. In addition to prolonging hospital stay and increasing healthcare costs, PONV may contribute to serious adverse events. PONV is known to be more common in morbidly obese patients [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Moreover, PONV has been reported in approximately 80% of bariatric procedures, and LSG appears to have the highest PONV incidence among standard bariatric operations [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Even when prophylaxis recommendations based on the Apfel risk score are applied, up to 82% of patients undergoing metabolic and bariatric surgery may still experience PONV in the post-anesthesia care unit (PACU) [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe present study aimed to investigate the effects of different fresh gas flow rates on body temperature and PONV in patients undergoing laparoscopic sleeve gastrectomy.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy design and setting\u003c/h2\u003e \u003cp\u003eThis single-center, randomized, prospective study was conducted in the operating rooms of Fırat University Hospital between 01/10/2022 and 01/05/2023. A total of 231 patients scheduled for laparoscopic sleeve gastrectomy due to morbid obesity were assessed. After exclusions and refusals, 161 patients were randomized into three groups according to the planned fresh gas flow (FGF) rate and completed the study (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEthics approval and informed consent\u003c/h3\u003e\n\u003cp\u003e \u003cstrong\u003eEthics approval\u003c/strong\u003e \u003cp\u003e was obtained from the Fırat University Faculty of Medicine Clinical Research Ethics Committee (07/09/2022, No. 222335). All eligible participants were informed about the study and provided written informed consent.\u003c/p\u003e \u003c/p\u003e\n\u003ch3\u003eParticipants: inclusion and exclusion criteria\u003c/h3\u003e\n\u003cp\u003ePatients aged 18\u0026ndash;65 years with American Society of Anesthesiologists (ASA) physical status III and body mass index (BMI)\u0026thinsp;\u0026gt;\u0026thinsp;40 kg/m\u0026sup2;, undergoing laparoscopic sleeve gastrectomy and consenting to participate were included.\u003c/p\u003e \u003cp\u003ePatients undergoing bariatric procedures other than sleeve gastrectomy; those younger than 18 years; with arrhythmia; left ventricular ejection fraction\u0026thinsp;\u0026lt;\u0026thinsp;30%; hepatic or renal dysfunction; a history of PONV in previous surgeries; a history of motion sickness; current active smoking; or ASA physical status IV were excluded.\u003c/p\u003e\n\u003ch3\u003eRandomization and group allocation\u003c/h3\u003e\n\u003cp\u003eUsing a sealed-envelope method, 161 patients were randomized into three groups according to the planned FGF rate:\u003c/p\u003e\n\u003cp\u003e\u0026bull; Normal-flow anesthesia (NFA) group (n\u0026thinsp;=\u0026thinsp;53): FGF 2 L/min\u003c/p\u003e\n\u003cp\u003e\u0026bull; Low-flow anesthesia (LFA) group (n\u0026thinsp;=\u0026thinsp;55): FGF 1 L/min\u003c/p\u003e\n\u003cp\u003e\u0026bull; Minimal-flow anesthesia (MFA) group (n\u0026thinsp;=\u0026thinsp;53): FGF 0.5 L/min\u003c/p\u003e\n\u003ch3\u003eAnesthesia management and monitoring\u003c/h3\u003e\n\u003cp\u003eAfter 3 minutes of preoxygenation with 100% oxygen at 10 L/min, anesthesia was induced using propofol 2\u0026ndash;3 mg/kg based on total body weight (Propofol\u0026reg; 1%, Fresenius, Germany), remifentanil 1 \u0026micro;g/kg based on ideal body weight (Ultiva\u0026reg;, GSK, USA), and rocuronium bromide 0.6\u0026ndash;0.8 mg/kg (Esmeron\u0026reg;, MSD, Germany). After adequate anesthetic depth was achieved, endotracheal intubation was performed. Esophageal and tympanic temperature probes were placed and temperature measurements were recorded.\u003c/p\u003e \u003cp\u003eMaintenance anesthesia consisted of sevoflurane (Sevorane\u0026reg;, 100% liquid, AbbVie, UK) and a remifentanil infusion based on ideal body weight at 0.05\u0026ndash;0.2 \u0026micro;g/kg/min. Additional rocuronium was administered as needed. Patients were ventilated to maintain an end-tidal CO₂ of 35\u0026ndash;45 mmHg, with a tidal volume of 8 mL/kg ideal body weight and an inspiratory-to-expiratory ratio of 1:2 to maintain normocapnia. At the end of surgery, residual neuromuscular blockade was reversed using sugammadex 2 mg/kg intravenously (Bridion\u0026reg;, MSD, Netherlands) based on ideal body weight. For PONV prophylaxis, metoclopramide 20 mg (Metpamid\u0026reg;, Safir Farma, Istanbul) was administered.\u003c/p\u003e \u003cp\u003eAn anesthesia workstation capable of low and minimal flow anesthesia (Maquet Flow-i C20\u0026reg;, Solna, Sweden) was used. Before induction, a self-test including a breathing circuit leak test was performed, and soda lime was checked to ensure adequate function.\u003c/p\u003e \u003cp\u003eAll operations were performed by the same surgical team, and intra-abdominal pressure was maintained below 15 mmHg. Operating room temperature was maintained at 22\u0026deg;C throughout surgery.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eFresh gas flow protocol\u003c/h2\u003e \u003cp\u003eIn the NFA group, after achieving the target minimum alveolar concentration (MAC), FGF was set to 2 L/min.\u003c/p\u003e \u003cp\u003eIn the LFA group, after achieving target MAC, FGF was set to 1 L/min. To maintain FiO₂ above 35%, oxygen concentration was increased as required. Sevoflurane concentration was adjusted to maintain target MAC.\u003c/p\u003e \u003cp\u003eIn the MFA group, after achieving target MAC, FGF was set to 0.5 L/min. To maintain FiO₂ above 35%, oxygen concentration was increased as required. Sevoflurane concentration was adjusted to maintain target MAC.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSample size calculation\u003c/h3\u003e\n\u003cp\u003eBefore the study, sample size calculation was performed using G*Power (version 3.1.9.2), informed by the literature and expert opinion. With a 95% confidence level and 95% power, at least 52 patients per group were required (total minimum n\u0026thinsp;=\u0026thinsp;156).\u003c/p\u003e\n\u003ch3\u003eData collection\u003c/h3\u003e\n\u003cp\u003eAfter positioning on the operating table, heart rate, end-tidal CO₂, SpO₂, mean arterial pressure (MAP), MAC, inspired CO₂ (FiCO₂), inspired oxygen fraction (FiO₂), and tympanic and esophageal temperatures were recorded every 10 minutes.\u003c/p\u003e \u003cp\u003eMAP was targeted to remain above 65 mmHg; vasopressor support was provided when MAP fell below 65 mmHg.\u003c/p\u003e \u003cp\u003eAfter arrival in the PACU, patients were monitored and heart rate, SpO₂, MAP, tympanic temperature, and PONV score (1: no nausea/vomiting; 2: nausea; 3: retching; 4: vomiting) were recorded at admission and at 10, 20, and 30 minutes. Patients with a Modified Aldrete Score of 9 or higher were discharged from the PACU.\u003c/p\u003e \u003cp\u003ePostoperative heart rate, SpO₂, MAP, tympanic temperature, and PONV score were recorded at 6, 12, and 24 hours postoperatively.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eOutcomes\u003c/h2\u003e \u003cp\u003eThe primary outcomes were changes in body temperature and PONV across the three FGF groups, evaluated both within and between groups.\u003c/p\u003e \u003cp\u003eSecondary outcomes were changes in hemodynamic parameters (heart rate, MAP, and SpO₂) across the three FGF groups, evaluated both within and between groups.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eAnalyses were performed using SPSS version 22 (SPSS Inc., Chicago, IL, USA). Categorical variables are presented as n (%), and continuous variables as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation. Between-group comparisons of categorical variables were conducted using the chi-square (Pearson) test. Normality was assessed using the Kolmogorov-Smirnov test. For comparisons among more than two groups, the Kruskal-Wallis test was used. Statistical significance was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eBaseline characteristics\u003c/h2\u003e \u003cp\u003eNo statistically significant differences were observed among the groups regarding demographic characteristics and anthropometric measurements (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\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\u003eComparison of demographic characteristics and anthropometric measurements among the groups.\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=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNFA (n\u0026thinsp;=\u0026thinsp;53)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLFA (n\u0026thinsp;=\u0026thinsp;55)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMFA (n\u0026thinsp;=\u0026thinsp;53)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep*\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\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\u003e39.2\u0026thinsp;\u0026plusmn;\u0026thinsp;12.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e35.7\u0026thinsp;\u0026plusmn;\u0026thinsp;11.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e37.1\u0026thinsp;\u0026plusmn;\u0026thinsp;9.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.335\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI (kg/m\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e44.6\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e45.9\u0026thinsp;\u0026plusmn;\u0026thinsp;5.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e43.8\u0026thinsp;\u0026plusmn;\u0026thinsp;6.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.573\u003c/p\u003e \u003c/td\u003e \u003c/tr\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\u003e27/26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30/25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e28/25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.297\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\u003e* p values were calculated using Kruskal-Wallis test for continuous variables and chi-square test for categorical variables.\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eHemodynamic parameters\u003c/h2\u003e \u003cp\u003ePerioperative SpO₂, heart rate, and MAP values did not differ significantly between groups (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eTemperature measurements\u003c/h2\u003e \u003cp\u003eEsophageal and tympanic temperature measurements differed significantly between groups starting from the 20th minute (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). This difference was mainly attributable to higher temperature values in the minimal-flow group (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003ePostoperative nausea and vomiting\u003c/h2\u003e \u003cp\u003ePONV incidence in the PACU and at postoperative 6, 12, and 24 hours was lowest in the minimal-flow group and highest in the normal-flow group. This difference was statistically significant (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eWith the rapid global increase in the number of individuals with morbid obesity, anesthesiologists increasingly encounter morbidly obese patients in surgical practice. Every surgical intervention carries multiple risks related to both surgery and anesthesia. One such risk, inadvertent perioperative hypothermia, is defined as a decrease in body temperature below 36\u0026deg;C from the preoperative period through the postoperative period (the first 24 hours after anesthesia). The reported incidence ranges from approximately 40% to 70% [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eUnder normal conditions, core temperature is regulated by the hypothalamus. When core temperature is around 37\u0026deg;C, deviations as small as 0.2\u0026deg;C activate the thermoregulatory system, adjusting heat production and distribution to maintain thermal homeostasis. Intravenous and inhalational anesthetics inhibit hypothalamic control and widen the interthreshold range from approximately 0.2\u0026deg;C up to 4\u0026deg;C, delaying thermoregulatory responses. In addition, immobility in a cool operating room environment, inhalation of cold gases, and heat losses from body cavities contribute to temperature decline. Thermal redistribution from the core to the periphery within the first hour of general anesthesia is a major driver of the initial rapid decrease in core temperature [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIndividuals with obesity have an increased layer of subcutaneous adipose tissue that acts as an insulating barrier due to its low thermal conductivity, thereby reducing conductive heat loss through the skin. Moreover, these patients may exhibit higher vasoconstriction thresholds, leading to earlier peripheral vasoconstriction and a more limited redistribution of heat from core to periphery. The magnitude of intraoperative core temperature decrease and redistribution hypothermia has been shown to be inversely related to body fat percentage and body surface area [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Studies comparing obese and non-obese patients have reported significantly higher intraoperative and postoperative temperatures in obese patients [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. However, it should also be considered that obese patients may be prone to substantial heat loss after prolonged exposure to hypothermia due to relatively lower muscle mass and a higher surface area-to-mass ratio [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eInadvertent perioperative hypothermia is clinically important because of its associated complications, including surgical site infection, postoperative ischemic myocardial events, increased intraoperative blood loss, increased PONV (and consequently a potential increase in anastomotic leak and rupture risk), and delayed postoperative recovery. Therefore, achieving and maintaining normothermia in the perioperative period is important for optimal surgical outcomes as well as patient safety and satisfaction [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Traditional approaches to prevent hypothermia during general anesthesia include warming intravenous fluids, using heat-and-moisture exchangers, forced-air warming blankets or radiant warmers, and increasing operating room temperature; low-flow anesthesia may also be considered [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn a prior study comparing high-, low-, and minimal-flow anesthesia, temperature distributions differed significantly between groups after the 20th minute. Body temperature values were similar in the low-flow and minimal-flow groups and higher than those in the high-flow group [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. In the present study of morbidly obese patients undergoing LSG, our findings were consistent with the literature and indicated that minimal-flow anesthesia better preserved intraoperative body temperature.\u003c/p\u003e \u003cp\u003eLow- and minimal-flow anesthesia techniques have been increasingly adopted in recent years because of potential environmental benefits, cost savings, and contributions to more physiologic respiratory conditions. These techniques are also known to better preserve the temperature and humidity of inspired gases, promoting thermal stability. Concerns persist regarding potential hemodynamic instability; however, the literature suggests that these techniques do not compromise hemodynamic stability and can be used safely [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Similarly, in our study, hemodynamic stability was maintained and no significant between-group differences were observed.\u003c/p\u003e \u003cp\u003ePONV is one of the most common complications after general anesthesia and is associated with multiple pathophysiologic mechanisms [\u003cspan additionalcitationids=\"CR21 CR22\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. In metabolic and bariatric surgery, PONV is a frequent complication. In a comprehensive review published in 2025, Jumaev et al. reported a high incidence of PONV after sleeve gastrectomy and highlighted multiple contributing factors [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Likewise, in a retrospective cohort study, Tan et al. showed that PONV incidence varies with anesthetic technique, body temperature, and hydration status [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe mechanisms of PONV are complex and influenced by numerous risk factors [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. A decline in intraoperative body temperature has been associated with prolonged extubation time, longer stay in intensive care units, and increased postoperative complications [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In a pediatric study, nausea incidence at postoperative 6 hours was significantly higher in children with body temperature below 36\u0026deg;C compared with those above 36\u0026deg;C [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. In our study, the higher temperature profile in the minimal-flow group may have contributed to the lower PONV incidence. The impact of thermoregulation on neuroendocrine pathways related to nausea perception may help explain these findings [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePreventing hypothermia by maintaining thermal balance has been suggested to reduce complications such as PONV. In a study of morbidly obese patients, maintaining core temperature above 36\u0026deg;C with forced-air warming significantly reduced PONV incidence [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Other studies likewise report lower nausea and vomiting rates in groups with better temperature preservation [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. These findings support the physiologic rationale for the lower PONV rates observed in our minimal-flow group.\u003c/p\u003e \u003cp\u003eThis study has several limitations. It was conducted at a single center and included patients treated within one institution, which may limit generalizability. The cohort was restricted to morbidly obese patients undergoing laparoscopic sleeve gastrectomy, and no comparisons were made with other surgical procedures. The semi-quantitative PONV scoring system may be subject to subjective interpretation. Individual factors that could influence thermoregulatory responses (e.g., menopausal status, endocrine disorders) were not standardized. Finally, follow-up was limited to 24 hours, and longer-term outcomes could not be assessed.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn conclusion, low- and minimal-flow anesthesia, when applied with close patient monitoring and modern anesthesia workstations, may be preferable because of potential environmental benefits, cost reduction, provision of more physiologic respiratory conditions, and attenuation of intraoperative hypothermia. Based on our findings, low- and minimal-flow anesthesia can be used safely in patients undergoing LSG, as these techniques maintained hemodynamic stability, better preserved body temperature, and reduced PONV incidence. Nevertheless, further studies with larger patient series are warranted.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eFunding: This study received no external funding.\u003c/p\u003e\n\u003cp\u003eConflict of Interest: The authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003eEthical Approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.\u003c/p\u003e\n\u003cp\u003eEthics committee approval was obtained from the local Clinical Research Ethics Committee (approval details blinded for review).\u003c/p\u003e\n\u003cp\u003eInformed Consent: Informed consent was obtained from all individual participants included in the study.\u003c/p\u003e\n\u003cp\u003eData Availability: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMasry MAME, Fiky MAME. 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Am J Transl Res. 2021;13(4):3459\u0026ndash;65.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"laparoscopic sleeve gastrectomy, low-flow anesthesia, minimal-flow anesthesia, hypothermia, postoperative nausea and vomiting","lastPublishedDoi":"10.21203/rs.3.rs-8671925/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8671925/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIntroduction: Inadvertent perioperative hypothermia and postoperative nausea and vomiting (PONV) remain common after metabolic and bariatric surgery (MBS). Fresh gas flow (FGF) may influence heat and humidity conservation within the breathing circuit and thereby affect perioperative temperature and PONV.\u003c/p\u003e\n\u003cp\u003eMethods: In this single-center, randomized, prospective trial, 161 adults with obesity class III (BMI \u0026gt; 40 kg/m²) scheduled for laparoscopic sleeve gastrectomy were allocated to normal-flow (2.0 L/min; n=53), low-flow (1.0 L/min; n=55), or minimal-flow anesthesia (0.5 L/min; n=53). Esophageal and tympanic temperatures and hemodynamic variables were recorded every 10 minutes intraoperatively. PONV was assessed in the post-anesthesia care unit (PACU) and at 6, 12, and 24 hours postoperatively.\u003c/p\u003e\n\u003cp\u003eResults: Baseline characteristics were comparable among groups. From the 20th minute onward, esophageal and tympanic temperatures differed between groups (p\u0026lt;0.001), with higher temperatures in the minimal-flow group. The proportion of patients without PONV in the PACU and at 6, 12, and 24 hours was highest with minimal-flow anesthesia and lowest with normal-flow anesthesia (p\u0026lt;0.05). Perioperative SpO₂, heart rate, and mean arterial pressure were similar across groups (p\u0026gt;0.05).\u003c/p\u003e\n\u003cp\u003eConclusion: Minimal-flow anesthesia (0.5 L/min) better preserved perioperative temperature and was associated with lower PONV after laparoscopic sleeve gastrectomy, without compromising hemodynamic stability.\u003c/p\u003e","manuscriptTitle":"Effects of Different Fresh Gas Flow Rates on Body Temperature and Postoperative Nausea and Vomiting in Morbidly Obese Patients Undergoing Laparoscopic Sleeve Gastrectomy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-30 01:37:17","doi":"10.21203/rs.3.rs-8671925/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7f4e757f-a40c-4dfc-be67-75571ed3edc8","owner":[],"postedDate":"January 30th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-09T18:24:39+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-30 01:37:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8671925","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8671925","identity":"rs-8671925","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}