Hemtanon N.Raykateeraroj N.Kongsayreepong S.Yuyen T.Boorapapon P.Hikasa Y.Lao-amornphunkul S.Kitisin N.Mahidol University2026-04-102026-04-102026-12-01BMC Anesthesiology Vol.26 No.1 (2026)https://repository.li.mahidol.ac.th/handle/123456789/116102Background: Both hypovolemia and fluid overload are associated with adverse outcomes in critically ill patients, yet many methods for assessing fluid responsiveness have limitations. The Trendelenburg maneuver, which transiently increases cardiac preload through a head-down tilt and operates on the same principle as passive leg raising but is easier to perform and more comfortable, may offer a practical adjunct in light-sedated patients under mechanical ventilation with spontaneous breathing activity, a common clinical scenario. Methods: In this single-center, prospective study, mechanically ventilated adults with spontaneous breathing and signs of tissue hypoperfusion in a surgical intensive care unit (ICU) underwent a standardized sequence of hemodynamic assessments: supine baseline (T0), reverse Trendelenburg + 10° (T1), Trendelenburg − 13° (T2), return to supine before fluid loading (F0), and reassessment after a 4 mL/kg infusion of 5% albumin over 15 min (FL). Hemodynamics (cardiac index [CI], stroke volume variation [SVV], pulse pressure variation [PPV], central venous pressure [CVP]) were measured with FloTrac™/HemoSphere™. Fluid responsiveness was defined as a ≥ 10% increase in CI from F0 to FL. The diagnostic performance of Trendelenburg-induced hemodynamic changes (Δ values, T2–T1) and baseline variables was evaluated using the area under the receiver operating characteristic curve (AUROC), and gray-zone analysis was performed to quantify diagnostic uncertainty. Results: Thirty-eight patients were included; 21 (55%) were classified as fluid responders. A ΔCI > 0.15 L/min/m² yielded an AUROC of 0.78 (95% confidence interval, 0.64–0.93), with 52.4% sensitivity and 82.4% specificity; however, more than 80% of patients fell within the gray zone. A Δ%CI > 6% showed similar performance, while ΔSVV and ΔPPV demonstrated lower but moderate accuracy. In sensitivity analyses, diagnostic performance decreased when fluid responsiveness was redefined as a ≥ 15% increase in CI, and was slightly lower among patients receiving norepinephrine < 0.1 µg/kg/min. Conclusions: The Trendelenburg maneuver was feasible and safe but showed limited and inconsistent diagnostic performance for predicting fluid responsiveness. With more than 80% of patients falling within wide gray zones, the test is inconclusive for most bedside decisions and should not be used as a stand-alone guide. Trial registration: Thai Clinical Trials Registry (TCTR20230704005) registered 4 July 2023.MedicineArticleSCOPUS10.1186/s12871-026-03706-12-s2.0-1050344320841471225341721238