Predictive value of pulse pressure variation for fluid responsiveness after maneuver to change tidal volume in patients with protective ventilatory strategy

Introduction

After the early phase of sepsis, excessive fluid administration may worsen pulmonary edema and prolong mechanical ventilation [1]. Accurately predicting fluid responsiveness obviates unnecessary fluid loading, and helps to detect patients who may benefit from a volume expansion. Pulse pressure variation (DPP) is a reliable predictor of fluid responsiveness in mechanically ventilated patients only when tidal volume is at least 8 ml/kg [2]. The aim of this study was to evaluate the predictive value of DPP for fluid responsiveness after a maneuver to change tidal volume to 8 ml/kg in patients ventilated with 6 ml/kg.

Methods

Prospective clinical study in 40 patients ventilated with 6 ml/kg after resuscitation phase of severe sepsis and septic shock. Fluid challenge was indicated by the attending physician (7 ml/kg of 6% hydroxyethyl starch 130/0.4). Complete hemodynamic measurements including DPP (DPP 6 ml/kg) were obtained at baseline. The tidal volume was then changed to 8 ml/kg and the DPP (DPP 8 ml/kg) was measured after 5 minutes. The ventilatory settings were returned to 6 ml/kg before fluid challenge. Patients whose cardiac output (CO) increased by ≥15% were considered to be fluid responders. Receiver operating characteristic (ROC) curve analysis was used to evaluate the predictive value of DPP.

Results

In 19 patients (responders), CO increased by >15% after fluid infusion. Fluid responsiveness was better predicted with DPP 6 ml/kg (ROC curve area 0.92 ± 0.05) than with pulmonary artery occluded pressure (0.56 ± 0.09) and right atrial pressures (0.74 ± 0.08). Increasing tidal volume to 8 ml/kg did not improved prediction as the ROC curve area with DPP 8 ml/kg was 0.94 ± 0.03. The best cut-off values defined by the ROC curve analysis was 6.5% and 10.5% for DPP 6 ml/kg and DPP 8 ml/kg, respectively.

Conclusions

The maneuver to change tidal volume to 8 ml/kg in patients ventilated with protective ventilatory strategy to better predict fluid responsiveness is not useful. Fluid responsiveness can be correctly predicted in patients ventilated with tidal volume of 6 ml/kg.