Impact of Trendelenburg angle on perioperative outcomes during gasless vNOTES surgeries: a retrospective comparative study.

This retrospective cohort study was approved by the Institutional Review Board of Chengdu Women’s and Children’s Central Hospital (No. 2022 − 112). We analyzed data from patients who underwent gasless vNOTES surgery at our institution between January 2022 and April 2024. Eligible patients were aged 18–60 years, diagnosed with benign gynecological diseases, scheduled for vNOTES under general anesthesia (ASA status I-III), and provided voluntary consent. Exclusion criteria included: no sexual activity, pregnancy/lactation, mental/psychiatric/neurological disorders, gynecological malignancy, inability to tolerate surgery/anesthesia,, or participation in other clinical trials within 3 months, prior abdominal surgeries (≥ 2), severe pelvic adhesions (documented via preoperative imaging or intraoperative findings), obliterated pouch of Douglas (due to endometriosis, pelvic inflammatory disease, or prior surgery), suspected infection/malignancy/rectovaginal endometriosis. Group allocation was based on the maintained intraoperative angle (≥ 80% of surgical duration). Initial planned angle was determined preoperatively (Low-Angle: BMI < 25 kg/m² + no prior abdominal surgery; Steep-Angle: institutional protocol for all other patients). Intraoperative angle adjustments (permitted only for inadequate exposure) were documented, and patients were analyzed in their original group to preserve allocation integrity—no patients required adjustments exceeding their group’s angle threshold. All procedures were performed by a single surgical team of three senior gynecologists with 12, 15, and 18 years of clinical experience, respectively. Each surgeon performs ≥ 50 vNOTES procedures annually and has completed > 100 vNOTES surgeries to date. All received standardized general anesthesia: induction with propofol (2–3 mg/kg), sufentanil (0.3–0.5 µg/kg), and cisatracurium (0.15–0.2 mg/kg), followed by sevoflurane titration to maintain bispectral index (BIS) between 40 and 60. Surgical site preparation followed aseptic protocols without gas insufflation. A single surgical team (three senior gynecologists, each with > 100 vNOTES experience) performed all procedures. Trendelenburg angle selection was protocol-driven: patients with BMI < 25 kg/m²and no prior abdominal surgery were initially assigned to low-angle positioning, with adjustments permitted only if intraoperative exposure was inadequate.Trendelenburg angle was measured using the operating table’s integrated digital inclinometer (± 1°), with real-time readings recorded at the start (T3) and end (T6) of surgery, and every 15 min intraoperatively. The mean angle over the surgical duration was used for group classification. Angle adjustments were prohibited after incision. Postoperative analgesia included parecoxib 40 mg IV at wound closure, oral celecoxib 200 mg twice daily for 48 h, and tramadol 50 mg IV for rescue (VAS > 4). A post-hoc power analysis (GPower 3.1) confirmed 89% power to detect a 24-hour VAS pain score difference of 0.66 (SD 0.35) at α = 0.05. Angle adjustments were permitted only if the surgical team documented inadequate exposure. No adjustments were made after incision to maintain group allocation integrity.Steep-Angle Group assignment followed institutional practice for gasless vNOTES at the time, which mandated ≥ 30° tilt for all pelvic procedures to align with published guidelines, even in patients with low BMI or uncomplicated anatomy. Anesthesia care was provided by a dedicated team of four attending anesthesiologists (10–14 years of experience) and two certified registered nurse anesthetists, all with ≥ 3 years of specialized experience in minimally invasive gynecologic surgery (including gasless vNOTES and steep Trendelenburg positioning). Standardized anesthesia protocols were followed across all cases to minimize variability.Gasless vNOTES technique: (1) General anesthesia with endotracheal intubation; (2) Lithotomy position with Trendelenburg tilt as per group allocation; (3) Vaginal preparation with povidone-iodine; (4) Placement of a GelPOINT V-Path transvaginal access port (Applied Medical, Rancho Santa Margarita, CA, USA) into the posterior vaginal fornix; (5) Abdominal wall retraction using a self-retaining wound retractor (Alexis ® O, Applied Medical) to create a surgical field (equivalent to 8–10 mmHg pneumoperitoneum); (6) Uterine manipulation with a rigid uterine manipulator (CooperSurgical, Trumbull, CT, USA) for optimal exposure; (7) No gas insufflation—ambient air was evacuated via passive drainage through the access port; (8) Standard laparoscopic instruments (5 mm) were used for hysterectomy, ovarian cystectomy, or fallopian tube surgery; (9) Closure of the vaginal cuff with absorbable sutures and pelvic irrigation with normal saline. VAS scores were assessed at 2 and 24 h postoperatively to capture acute pain (2 h) and subacute pain (24 h). Intermediate time points (6/12 h) were not included due to institutional postoperative monitoring protocols, but patients received scheduled oral celecoxib (200 mg twice daily) and rescue tramadol (50 mg IV) for VAS > 4 between assessments to ensure adequate pain control. We collected comprehensive perioperative data encompassing hemodynamic parameters (diastolic blood pressure [DBP], systolic blood pressure [SBP], heart rate [HR], and airway pressure) measured at specific time points during surgery: pre-anesthesia (T0), immediately after tracheal intubation (T1), 10 min post-endotracheal intubation (T2), at the start of surgery (T3), at the end of surgery (T6), and upon operating room discharge (T8). Additional perioperative metrics included time to surgery, time to anesthesia, intraoperative blood loss, conversion rate, and anesthetic consumption. Postoperative outcomes assessed were visual analog scale (VAS) scores for abdominal pain at 2 and 24 h postoperatively, shoulder pain, and postoperative nausea and vomiting (PONV), alongside intraoperative and postoperative complications, as well as recovery milestones such as time to first anal exhaust and time to first eating. All statistical analyses were conducted using SPSS version 26.0 (IBM Corp., Armonk, NY, USA). Continuous variables with normal distribution were expressed as mean ± standard deviation (SD), whereas non-normally distributed data were reported as median with interquartile range [M (P25, P75)]. Categorical variables were presented as frequencies and percentages (n, %). Between-group comparisons utilized independent samples t-tests for normally distributed continuous variables and Mann-Whitney U tests for non-parametric data, with categorical variables analyzed using chi-square tests or Fisher’s exact tests as appropriate. Statistical significance was defined as a two-tailed p-value < 0.05. For repeated-measures data (airway pressure, HR, SBP, DBP) at multiple intraoperative time points, linear mixed-effects models were used to account for within-subject correlations, with group (Low-Angle vs. Steep-Angle) as a fixed effect and patient as a random effect. The unstructured covariance structure was selected based on Akaike Information Criterion (AIC) to optimize model fit. Normality of residuals was confirmed via Q-Q plots and Shapiro-Wilk tests (all p  > 0.05). A post-hoc power analysis (GPower 3.1) confirmed 89% power to detect a 24-hour VAS pain score difference of 0.66 (SD 0.35) at α = 0.05, supporting the sample size adequacy for detecting clinically relevant differences in the primary pain outcome.

The two groups had similar characteristics(Table  1 ). There were no statistically significant differences between two groups in terms of age, BMI, number of vaginal births, number of abdominal surgeries, and ASA grade. There was no statistically significant difference in the surgical composition ratio between the two groups ( p  > 0.05). The Low-Angle Group consisted of 10 cases of hysterectomy (with or without adnexectomy),30 cases of fallopian tube surgery, 12cases of ovarian cystectomy and adnexectomy. The steep-Angle Group included 12 cases of hysterectomy (with or without adnexectomy), 28 cases of fallopian tube surgery, and 10 cases of ovarian cystectomy. Table 1 Baseline clinical characteristics of 102 patients Variable steep-Angle Group  (N=50) Low-Angle Group (N=52) t/χ 2  P  Age (years), mean (SD)  35.04(9.7) 35.41(9.4) 1.10 0.887 weight (kg), mean (SD)  56.3(16.01) 55.3(11.85) 1.33 0.601 Height (cm), mean (SD)  161.3(4.37) 159.66(5.67) 0.65 0.258 BMI(body mass index, kg/m 2 ) 21.6(2.3) 21.7(1.7) 0.57 0.841 Hypertension, n (%)  1(4%) 2(0.76%) 0.75 0.657 Diabetes, n (%)  1(4%) 0 - 1.000 ASA classification   I 15(60%)10(40%) 14(53.8%)12(46.2%) 0.12 0.691  II 10(40%) 12(46.2%) ASA (American Society of Anesthesiologists) Baseline clinical characteristics of 102 patients ASA (American Society of Anesthesiologists) There is no statistically significant difference (4%vs4.3%, p  > 0.05)between the Steep-Angle group and the Low-Angle group in terms of conversion rate. Intraoperative hemodynamic parameters were comparable between groups (Table  2 ), with no significant differences in SBP, DBP, HR, or airway pressure at any time point. HR, DBP, SBP and airway pressure came from repeated measurements of the same individual at different time points, indicating the presence of a two-level structure in the data. The estimation results showed that there is no statistically significant difference between the Low-Angle Group and the Steep-Angle Group in terms of HR, DBP, SBP and airway pressure at different time point during surgery. Statistical analysis revealed no statistically significant hemodynamic differences between both groups.Mean SBP values remained within 110–120 mmHg range ( p  > 0.05), with maximum variation of 12% from baseline. DBP showed similar stability (68–82 mmHg, p  > 0.05). HR patterns demonstrated expected physiological responses - transient tachycardia post -intubation (mean + 14 bpm) followed by anesthesia-induced bradycardia (58–64 bpm), with complete recovery by T8 ( p  = 0.61). Airway pressures maintained strict proportionality to tidal volumes in both groups (12–17 cmH 2 O, p  > 0.05)(Fig.- 1  A, B,C, D). Table 2 A summary of the main outcomes Variable steep-Angle Group  (N=25) Low-Angle Group (N=26) t/χ 2 P T0 HR (bpm), mean (SD) 77.2(10.3) 77.8(15.4) 1.52 0.618 SBP (mmHg), mean (SD) 114.5(13.2) 124.1(15.1) 1.87 0.632 DBP (mmHg), mean (SD) 72.1(7.8) 77.5(9.2) 0.54 0.058 T1 HR (bpm), mean (SD) 78.0(12.2) 72.8(17.4) 1.72 0.229 SBP (mmHg), mean (SD) 107.7(15.1) 111.8(17.2) 1.03 0.374 DBP (mmHg), mean (SD) 67.0(9.1) 71.9(13.6) 1.11 0.143 Airway pressure (cmH 2 O), mean (SD) 11.7(2.5) 11.8(1.8) 0.45 0.841 T2 HR (bpm), mean (SD) 66.8(9.2) 61.0(9.4) 0.46 0.056 SBP (mmHg), mean (SD) 97.0(14.4) 98.3(11.0) 0.11 0.702 DBP (mmHg), mean (SD) 56.8(9.3) 59.3(9.2) 0.04 0.343 Airway pressure (cmH 2 O), mean (SD) 11.8(2.4) 12.0(1.7) 1.96 0.539 T3 HR (bpm), mean (SD) 65.2(9.2) 60.0(10.9) 0.83 0.079 SBP (mmHg), mean (SD) 95.6(9.1) 99.1(11.7) 1.12 0.246 DBP (mmHg), mean (SD) 56.5(6.7) 60.5(10.7) 1.35 0.114 Airway pressure (cmH 2 O, mean (SD) 12.0(2.7) 12.5(2.3) 0.01 0.525 T6 HR (bpm), mean (SD) 63.6(8.2) 64.6(9.7) 0.48 0.983 SBP (mmHg), mean (SD) 98.1(8.3) 104.9(9.6) 0.98 0.101 DBP (mmHg), mean (SD) 58.4(9.1) 65.1(8.8) 0.44 0.127 Airway pressure (cmH 2 O, mean (SD) 13.4(2.8) 13.6(2.0) 1.34 0.847 T8 HR (bpm), mean (SD) 83.9(12.2) 84.9(11.4) 0.14 0.775 SBP (mmHg), mean (SD) 117.2(12.2) 120.7(12.4) 0.04 0.336 DBP (mmHg), mean (SD) 75.1(9.5) 76.8(8.1) 1.26 0.491 A summary of the main outcomes Fig. 1 Comparisons of heart rate (HR, A ), systolic blood pressure (SBP, B ), diastolic blood pressure (DBP, C ), and airway pressure ( D ) between Low-Angle (≤20°) and Steep-Angle (≥30°) Groups at key time points: T0 (pre-anesthesia), T1 (immediately post-intubation), T2 (10 min post-intubation), T3 (start of surgery), T6 (end of surgery), T8 (OR discharge). Data are presented as mean ± SD; no statistically significant differences were observed between groups (all p>0.05). Intraoperative Hemodynamic and Airway Pressure Outcomes by Group Comparisons of heart rate (HR, A ), systolic blood pressure (SBP, B ), diastolic blood pressure (DBP, C ), and airway pressure ( D ) between Low-Angle (≤20°) and Steep-Angle (≥30°) Groups at key time points: T0 (pre-anesthesia), T1 (immediately post-intubation), T2 (10 min post-intubation), T3 (start of surgery), T6 (end of surgery), T8 (OR discharge). Data are presented as mean ± SD; no statistically significant differences were observed between groups (all p>0.05). Intraoperative Hemodynamic and Airway Pressure Outcomes by Group Table  3 summarized the other outcomes. There is no statistically significant difference between the Steep-Angle group and the Low-Angle group in terms of surgical time, intraoperative blood loss, anesthesia time, anesthesia consumption, VAS and PONV scores at 2 h post surgery, postoperative and intraoperative complications, time to first anal exhaust, eating, and getting out of bed after surgery. Table 3 A summary of the other outcomes Variable steep-Angle Group (N=25) Low-Angle Group (N=26) t/χ 2 P surgical time,mean (SD) 65.52(22.78) 72.84(24.91) 0.01 0.279 intraoperative blood loss, mean (SD) 58.45(12.602) 62.10(11.496) 0.83 0.382 anesthesia time, mean (SD) 90.80(25.16) 98.30(25.31) 0.01 0.294 anesthesia consumption(Sufenta), mean (SD) 21.82(6.14) 18.54(3.90) 1.63 0.424 VAS score for abdominal pain 2 h after surgery, mean (SD) 2.36(0.67) 1.57(0.80) 1.28 0.225 VAS score for shoulder pain 2 h after surgery, mean (SD) 1.32(0.60) 1.38(0.46) 1.01 0.317 VAS score for abdominal pain 24 h after surgery, mean (SD) 1.12(0.42) 0.46(0.28) 1.85 0.042 VAS score for shoulder pain 24 h after surgery, mean (SD) 0.76(0.52) 0.54(0.79) 1.06 0.292 PONV scores at 2 h post surgery, mean (SD) 0.48(1.22) 0.5(1.99) 0.39 0.996 PONV scores at 24 h post surgery, mean (SD) 0.36(1.43) 0.00(0.00) 0.11 0.208 postoperative and intraoperative complications,n (%) 2(8%) 1(3.8%) 0.65 0.192 time to first anal exhaust, mean (SD) 11.1(6.9) 10.9(6.2) 0.09 0.923 time to first eat,mean (SD) 11.84(6.4) 10.96(5.2) 0.53 0.596 time to get out of bed after surgery,mean (SD) 11.3(7.8) 10.4(7.6) 0.38 0.701 visual analogue scale,VAS; postoperative nausea and vomiting,PONV A summary of the other outcomes visual analogue scale,VAS; postoperative nausea and vomiting,PONV The VAS in shoulder pain in the Low-Angle group at 24 h post surgery was lower than that in the Steep-Angle group (0.34 vs. 0.76; p  = 0.142).While the Low-Angle Group had significantly lower 24-hour abdominal pain VAS (0.46 ± 0.28 vs. 1.12 ± 0.42, p  = 0.014), both scores reflect mild pain levels under standardized multimodal analgesia. Pain assessment was limited to subjective VAS scores, with no objective markers (e.g., inflammatory cytokines) measured.

This study establishes that minimizing Trendelenburg positioning intensity to ≤ 20° during gasless vNOTES for benign gynecologic surgery achieves outcomes equivalent to conventional steep-angle approaches, while significantly reducing postoperative patient discomfort. The low-angle strategy preserves hemodynamic and respiratory stability, maintains surgical feasibility, and does not increase perioperative risks or technical failure. Critically, it represents a patient-centered advancement by mitigating unnecessary physiological stress and iatrogenic pain linked to extreme positioning. The reduction in postoperative abdominal pain, while statistically significant, supports positioning optimization rather than a paradigm shift in pain management.These results support the hypothesis that reduced tilt may improve safety in high-risk patients, where steep positioning’s physiological effects are more likely to manifest. These exploratory findings suggest that routine steep Trendelenburg positioning may not be necessary for uncomplicated gasless vNOTES, generating a hypothesis that warrants further validation in prospective trials.Further more trials are needed to verify the benefit.

Our study demonstrated that steep Trendelenburg positioning is not routinely required to achieve optimal surgical exposure in gasless vNOTES for benign gynecologic procedures. The results indicate that moderate Trendelenburg tilt offers comparable intraoperative visualization and technical feasibility while preserving procedural safety and efficiency. This positioning protocol is associated with a reduction in postoperative patient discomfort and maintains superior hemodynamic and respiratory stability during surgery. This study provides preliminary observational evidence that reduced Trendelenburg positioning (≤ 20°) may be a feasible alternative to steep angles in uncomplicated gasless vNOTES. These findings generate the hypothesis that routine steep positioning may not be necessary for benign gynecologic vNOTES, warranting confirmation in prospective trials. Our analysis reveals profound differences in positioning practices between surgical specialties, notably that vaginal surgeons employed substantially greater variability in Trendelenburg angles compared to laparoscopic counterparts. Where vaginal surgeons demonstrated median maximum tilt variations spanning 6° to 18°,reflecting individualized adjustments based on procedural demands, laparoscopic practitioners clustered within a narrow 21°–25° range [ 16 – 18 ]. This adaptability translated to clinically meaningful reductions in steep positioning exposure: vaginal cases spent only 10 median minutes at maximum tilt versus 116–117 min in laparoscopic or robotic approaches [ 18 , 19 ]. Such efficiency stems from dynamic intraoperative repositioning targeting brief critical phases rather than sustaining steep angles unnecessarily, contrasting sharply with the static positioning paradigms dominating robotic surgery. The persistent endorsement of steep Trendelenburg in robotic gynecologic surgery appears rooted in historical precedent rather than scientific validation—a concerning paradigm transfer from urologic and gynecologic oncology literature without procedure-specific justification [ 20 – 23 ]. Such terminological inconsistency underscores a critical absence of biological rationale or outcome data supporting extreme tilt in benign gynecology. The study by Huang [ 15 ] had shown that vaginal surgery data (where surgeons successfully operate at ≤ 18° tilt) fundamentally challenge this dogma, revealing that rigid adherence to steep angles likely represents institutional habit rather than anatomical necessity. Collectively, these findings necessitate a paradigm shift toward precision positioning strategies that prioritize physiological safety over arbitrary angle targets. Gasless vNOTES outcomes confirm that exposure for benign procedures can be reliably achieved at ≤ 20° through mechanical retraction, eliminating dependency on gravity, driven bowel displacement that necessitates steep angles in conventional laparoscopy [ 11 , 24 ]. Clinicians should emulate vaginal surgeons’ adaptive techniques: dynamically modulating tilt (e.g., transiently increasing to 18° during cystectomy dissection versus maintaining 6° during suturing) to minimize cumulative physiological stress while preserving exposure [ 5 , 15 ]. Real-time monitoring of airway pressures, cerebral oximetry, or intraocular pressure should supersede numeric angle targets, particularly as robotic platforms expand into benign gynecology [ 25 – 27 ]. By abandoning imported positioning dogmas in favor of patient- and procedure-specific optimization, minimally invasive surgery can reconcile technical efficacy with reduced iatrogenic burden. This study suggest equivalent hemodynamic profiles, reflected in non-significant differences in heart rate, systolic/diastolic blood pressure, and oxygen saturation, between low-angle (≤ 20°) and steep-angle (≥ 30°) positioning during gasless vNOTES. This an exploratory finding challenges traditional concerns that reduced Trendelenburg tilt compromises circulation, as the absence of pneumoperitoneum in gasless techniques avoids two key stressors inherent to conventional laparoscopy: (1) CO₂-induced depression of myocardial contractility, and (2) elevated intra-abdominal pressure (IAP > 12 mmHg) compressing the inferior vena cava and reducing venous return. Crucially, the mean 20.1° vs. 30.8° tilt differential represents a physiologically marginal difference for cardiovascular adaptation, well below the 35°–45° range where venous congestion and baroreceptor-mediated tachycardias typically manifest, while mechanical vaginal retraction maintains surgical exposure without gravitational reliance [ 13 , 14 ]. Consequently, clinicians may confidently prioritize lower angles in benign gynecologic vNOTES, leveraging gasless methodology to eliminate hemodynamic tradeoffs and reaffirming that avoidance of extreme positioning mitigates physiological strain without sacrificing circulatory stability or conversion rates (4.0% vs. 4.3%, p  = 0.319). Airway pressure remained equivalent between low-angle (≤ 20°) and steep-angle (≥ 30°) positioning throughout gasless vNOTES surgery ( p  > 0.05 at all phases), demonstrating that respiratory mechanics are inherently uncoupled from gravitational tilt in this transvaginal approach. The comparable airway pressures despite angle differences may be attributed to the absence of pneumoperitoneum, which may mitigate CO₂-induced diaphragmatic compression. Mechanical retraction in gasless vNOTES (generating 8–10 mmHg equivalent pressure) likely maintained constant respiratory mechanics irrespective of gravitational tilt [ 27 , 28 ]. This respiratory stability, maintained even at a mean 30.8° tilt, confirms that the traditional barotrauma risks associated with steep positioning are primarily pneumoperitoneum -dependent rather than angle-dictated. Consequently, surgeons can safely prioritize ≤ 20° positioning without ventilatory compromises, aligning with core anesthesia goals to minimize plateau pressure elevations while preserving surgical exposure. The present study demonstrates that reducing Trendelenburg positioning intensity during gasless vNOTES does not compromise surgical feasibility or patient safety. Crucially, the absence of a statistically significant difference in conversion rates between the Low-Angle group (4.0%) and Steep-Angle group (4.3%, p  = 0.319) confirms that adequate operative exposure can be achieved at angles ≤ 20°. This challenges the dogma that steeper angles are mandatory for successful transvaginal endoscopic procedures. The low overall conversion rate (4.26% across all cases) further validates vNOTES as a viable minimally invasive approach for benign gynecologic pathology, irrespective of positioning intensity and it was similar with the study by Wang et al., [ 28 ]. Reduced angles did not compromise surgical outcomes. Operative duration, blood loss, postoperative complications, the rates of. PONV, hospital stays and conversion rates remained equivalent regardless of tilt severity.This technical parity stems from vNOTES’ unique anatomical advantages: vaginal retractors generate tissue tension equivalent to 8–10 mmHg pneumoperitoneum—replacing gravitational bowel displacement; dynamic uterine manipulation creates “optical triangulation,” maintaining visualization without steep tilts; and direct transvaginal access avoids the abdominal wall resistance encountered in laparoscopy. While our study focused on low-risk patients (BMI 18–25 kg/m², ASA I–II), gasless vNOTES with reduced Trendelenburg may offer unique benefits for high-risk populations. Obese patients (BMI > 30 kg/m²) often face increased IOP and ventilatory compromise with steep tilt; gasless techniques eliminate CO₂-related hypercapnia, and ≤ 20° tilt reduces abdominal wall compression on the diaphragm [ 29 ]. Similarly, patients with cardiopulmonary comorbidities (e.g., heart failure, chronic obstructive pulmonary disease) may benefit from reduced venous congestion and preserved hemodynamic stability—findings supported by literature showing reduced physiological stress with moderate tilt in complex cases [ 14 ]. Future trials should prioritize these populations to validate safety and efficacy. Although 24-hour abdominal pain scores remained low overall (VAS < 1.2), the statistically significant elevation in the Steep-Angle group (1.12 vs. 0.46, p = 0.014) reflects biologically consequential peritoneal stress. This increase aligns mechanistically with cephalad visceral displacement under steep angles, which tensions mesenteric attachments and peritoneal surfaces [ 30 ].Prior studies [ 11 , 13 , 30 ] have proposed that gravitational visceral displacement may contribute to postoperative pain, though this mechanism was not directly tested in our study. Prior robotic and NOTES studies confirm such gravitational forces elevate inflammatory cytokines (IL-6, TNF-α) proportional to tilt angle, effects dissociated from CO₂-related acidosis in our gasless vNOTES model [ 27 , 30 ]. Thus, while multimodal analgesia optimized baseline control, angle reduction conferred a tangible anti-nociceptive advantage—a strategy aligning with ERAS (Enhanced Recovery After Surgery) principles of minimizing preventable stressors.“The 0.66-point reduction in 24-hour abdominal pain VAS (0.46 vs. 1.12) exceeds the minimal clinically important difference (MCID) of 0.5–0.6 established for postoperative pain.The observed pain difference may be related to reduced peritoneal tension from gravitational visceral displacement, though this mechanism is speculative as we did not measure inflammatory mediators or peritoneal stress directly. Additionally, the 24-hour follow-up period limits conclusions about longer-term pain outcomes. Integrating our findings with existing literature yields a risk-adapted positioning framework. For patients with BMI  30 may require 25–30° due to adipose displacement mechanics, but only after retractor optimization fails. Severe adhesions occasionally necessitate 25–30° for panoramic exposure, while cardiopulmonary compromised patients benefit most from ≤ 20° tilt to preserve hemodynamic stability [ 31 – 33 ]. The present study used general anesthesia due to institutional preference for airway control during transvaginal endoscopic surgery. However, reduced Trendelenburg tilt (≤ 20°) may enable regional anesthesia (e.g., spinal-epidural) in selected cases, as it minimizes the risk of airway obstruction and venous pooling associated with steep tilt. Regional anesthesia could further reduce postoperative pain and opioid consumption, aligning with ERAS principles—this warrants exploration in future prospective studies. This study has several limitations. First, the sample size ( n  = 102), though adequate for primary outcomes, lacks power to detect subtle differences in secondary endpoints like shoulder pain (Type II error risk).This is a single-center retrospective observational study of low-risk patients, which inherently carries a risk of selection bias and unmeasured confounding—particularly given non-randomized group assignment based on BMI and surgical history. Second, its single-center retrospective design may introduce selection bias, particularly regarding evolving intraoperative angle selection protocols by participating surgeons. Third, the strict BMI inclusion criteria (18–25 kg/m²) limits generalizability to obese populations where steep positioning may still be warranted. Future prospective trials are needed to evaluate whether reduced Trendelenburg positioning offers meaningful safety or pain benefits in obese patients or those with cardiopulmonary comorbidities, where steep tilt may pose greater physiological stress. A key limitation is the non-randomized, protocol-based group assignment, which was influenced by preoperative factors (BMI < 25 kg/m² + no prior abdominal surgery for Low-Angle Group). This introduces potential selection bias, as unmeasured confounding variables may have influenced both angle assignment and outcomes. Fouth, a key limitation is the lack of assessment of IOP, ICP, CBF, and cerebral autoregulation — parameters linked to steep Trendelenburg-related complications (e.g., visual disturbances, cerebral edema) [ 34 – 35 ]. Due to the retrospective design, these data were not collected; future prospective studies should integrate noninvasive monitoring to elucidate physiological thresholds for tilt-related risks in gasless vNOTES [ 36 ]. Though statistically significant, 24-hour abdominal pain was assessed only via VAS; the absence of serological biomarkers precludes objective quantification of positioning-related inflammatory stress. Postoperative follow-up was restricted to 24 h, missing potential delayed complications.

The vagina is the most widely used natural channel because it provides safe access to the peritoneal cavity [ 1 , 2 ]. Transvaginal natural orifice transluminal endoscopic surgery (vNOTES) is successfully applied in gynecologic surgery [ 3 , 4 ]. Positioning of the patient in the proper Trendelenburg position is essential in gynecologic surgery in vNOTES to achieve adequate exposure, especially in robotic surgery. Steep Trendelenburg (defined as 30–40 degrees ‘‘head down tilt’’) is routinely recommended in robotic-assisted urologic and gynecologic surgery to maximize exposure, often at the expense of potential morbidity, position migration, and ventilation difficulty. That have shown the risk of these complications to increase with prolonged surgery and steeper Trendelenburg [ 5 – 7 ]. Intraocular pressure increases significantly when patients are placed in the steep Trendelenburg position during gynecologic minimally invasive surgery [ 8 ]. Yet, there is minimal literature in objective assessment of degree of Trendelenburg positioning in vNOTES. Conventional laparoscopy employs CO₂ pneumoperitoneum to create surgical workspace but induces systemic complications including hypercapnic acidosis (PaCO₂ elevation > 15 mmHg in 38% of cases [ 9 , 10 ]), tachycardia/arrhythmias, and postoperative shoulder pain (68% incidence). Gasless vNOTES [ 11 – 13 ] overcomes these limitations via transvaginal access, where abdominal wall retractors and uterine manipulators establish stable operative fields at ≤ 20° Trendelenburg tilt. This reduces intraocular pressure elevation by 71% while achieving equivalent procedural success rates (95–100%) and eliminating cardiopulmonary stress from steep positioning. By leveraging vaginal anatomy, vNOTES resolves the exposure-conversion challenge of traditional gasless methods while mitigating risks associated with both pneumoperitoneum and extreme positioning. And more, the study by Aggarwal et al. [ 14 ] had shown that a mean angle of 20.5˚ was overall sufficient and associated with improved outcomes in robotic urologic pelvic surgical procedures when compared with the standard of 30˚.Gasless vNOTES leverages direct transvaginal instrumentation and abdominal wall retraction, potentially reducing angle requirements to ≤ 15° as demonstrated in Huang et al.‘s [ 15 ]2022 vNOTES hysterectomy series (mean 16.2° ± 3.5°). So, demand for steep Trendelenburg positioning is seldom needed when a gasless vNOTES approach to performing similar procedures is chosen, a retrospective study that prodded us to study the necessity of routine steep Trendelenburg positioning in gasless vNOTES. This retrospective observational study compares perioperative outcomes between protocol-assigned low-angle (≤ 20°) and steep-angle (≥ 30°) Trendelenburg positioning in gasless vNOTES.