Efficacy of trendelenburg maneuver in determining preoperative fluid deficit in spinal surgery

This study is a prospective, clinical cross-sectional study designed to evaluate the efficacy of the Trendelenburg maneuver in determining preoperative fluid deficit in spinal surgery. The aim of the study was to evaluate the efficacy of the Trendelenburg maneuver in predicting fluid response in elective spinal surgery patients ventilated with low tidal volume in the prone position and to examine its correlation with end-tidal CO₂. The study was conducted in the Department of Anesthesiology and Reanimation, Faculty of Medicine, Van Yüzüncü Yıl University. The sample size was calculated as 81 patients for a fluid deficit incidence rate of 30%, 5% Type I error, and a power value of approximately 80% at the 95% confidence level. The study included patients in the ASA I-II group, aged 18-65 years, who were scheduled for elective spinal surgery. A total of 82 patients were included in the study, 6 patients were excluded due to various complications and the data of 76 patients were analyzed. After induction of anesthesia, invasive arterial monitoring was performed and Trendelenburg maneuver was performed for one minute after the prone position was given, the patients waited for 3 minutes after the maneuver and then 500 ml intravenous crystalloid fluid was loaded within 10 minutes. Hemodynamic parameters and end-tidal CO₂ values were recorded at five different time points: before induction of anesthesia, before the Trendelenburg maneuver, immediately after the maneuver was terminated, 3 minutes after the maneuver was terminated, and after 500 ml fluid loading. Patients with a 10 mmHg increase in systolic blood pressure or a 2 mmHg increase in EtCO₂ after fluid loading were considered "fluid responsive". Of the patients included in the study, 52.6% were female and 47.4% were male. The mean age was 45.95±10.21 years. 21.1% of the patients were ASA I and 78.9% were ASA II. Regarding the type of operation, 80.3% of the patients underwent lumbar disc surgery. Fluid response was positive in 46.1% of the patients. There was no statistically significant difference between the groups with and without fluid response in terms of demographic and clinical characteristics. When hemodynamic parameters were analyzed, baseline EtCO₂ values were significantly lower in the group with fluid response (p=0.027). HR values measured immediately after Trendelenburg maneuver were significantly higher in the group with fluid response (p=0.027). After 500 ml fluid loading, the values of OAB, SAB, DAB and EtCO₂ were significantly higher in the group with fluid response. When the effect of Trendelenburg maneuver on EtCO₂ values was examined, no significant change was observed between before and after the maneuver (p=0.366), but EtCO₂ values decreased significantly at 3 minutes after the maneuver (p<0.001). After 500 ml of fluid resuscitation, EtCO₂ values increased again to pre-maneuver levels. According to the results of ROC analysis, the EtCO₂ change measured immediately after the Trendelenburg maneuver (%Δ EtCO₂ Measurement 2 - Measurement 1) showed moderate diagnostic performance with a sensitivity of 48.6% and specificity of 75.6% at a threshold value of 1.5% (AUC=0.644, p=0.031). EtCO₂ change measured 3 minutes after Trendelenburg maneuver did not have a statistically significant diagnostic value (AUC=0.603, p=0.122). EtCO₂ change measured after 500 ml fluid loading (%Δ EtCO₂ Measurement 4 - Measurement 1) showed superior diagnostic performance with 91.4% sensitivity and 97.6% specificity at a threshold value of 1.5% (AUC=0.957, p<0.001). The results of the study suggest that the Trendelenburg maneuver alone has limited efficacy in determining preoperative fluid deficit. EtCO₂ changes during the maneuver have moderate diagnostic value in predicting fluid responsiveness. However, EtCO₂ changes after fluid loading have high sensitivity and specificity in determining preoperative fluid deficit. Keywords: Spinal Surgery, Fluid Responsiveness, Trendelenburg Maneuver.