The Trendelenburg position decreases the threshold of dynamic variables in predicting fluid responsiveness: A prospective observational study.

Background: Goal-directed fluid therapy (GDFT) individualizes fluid administration to optimize oxygen delivery and tissue perfusion. Traditional static parameters, such as central venous and pulmonary artery wedge pressures, are inaccurate. Instead, GDFT employs dynamic variables like stroke volume variation (SVV) and pulse pressure variation (PPV) to assess preload responsiveness and guide fluid administration. However, the Trendelenburg position alters cardiovascular physiology, and the effects of different tilt angles on SVV, PPV, and other hemodynamic variables remain unclear.

Methods: This single-center, observational study enrolled patients undergoing elective surgery. Following induction of general anesthesia, patients were positioned supine (0°) and then in the Trendelenburg position, with the angle adjusted to 5°, 10°, 15°, and 25°. Dynamic variables, including SVV, PPV, contractility (d P /d t ), dynamic arterial elastance (Eadyn), and cardiac index (CI), at each angle were recorded and analyzed.

Results: A total of 27 patients (mean age 66.7 ± 11.7 years, 79% male) were included. Increasing the Trendelenburg tilt angle from 0° to 25° was associated with a significant reduction in SVV (12.21 ± 4.26% at 0° to 6.94 ± 2.37% at 25°, p < 0.001) and PPV (13.47 ± 4.27% at 0° to 6.81 ± 3.20% at 25°, p < 0.001). SVV and PPV measured in the supine position correlated significantly with values obtained at 5°, 10°, 15°, and 25° ( p < 0.001). d P /d t progressively declined from 711.85 ± 235.58 mmHg/s at 0° to 583.85 ± 166.19 mmHg/s at 25° ( p < 0.001), and CI decreased from 2.51 ± 0.59 L/min/m² to 2.27 ± 0.60 L/min/m² ( p = 0.001). Eadyn trended downward but did not reach statistical significance ( p = 0.088).

Conclusion: The thresholds of SVV and PPV for predicting fluid responsiveness decrease with progressive Trendelenburg tilt. These variables should therefore be interpreted cautiously in relation to tilt angle when guiding fluid management.