Pulse pressure variation and prediction of fluid responsiveness in patients ventilated with low tidal volumes

OBJECTIVE: To determine the utility of pulse pressure variation (Δ(RESP)PP) in predicting fluid responsiveness in patients ventilated with low tidal volumes (V(T)) and to investigate whether a lower Δ(RESP)PP cut-off value should be used when patients are ventilated with low tidal volumes. METHOD: This cross-sectional observational study included 37 critically ill patients with acute circulatory failure who required fluid challenge. The patients were sedated and mechanically ventilated with a V(T) of 6-7 ml/kg ideal body weight, which was monitored with a pulmonary artery catheter and an arterial line. The mechanical ventilation and hemodynamic parameters, including Δ(RESP)PP, were measured before and after fluid challenge with 1,000 ml crystalloids or 500 ml colloids. Fluid responsiveness was defined as an increase in the cardiac index of at least 15%. ClinicalTrial.gov: NCT01569308. RESULTS: A total of 17 patients were classified as responders. Analysis of the area under the ROC curve (AUC) showed that the optimal cut-off point for Δ(RESP)PP to predict fluid responsiveness was 10% (AUC = 0.74). Adjustment of the Δ(RESP)PP to account for driving pressure did not improve the accuracy (AUC = 0.76). A Δ(RESP)PP≥10% was a better predictor of fluid responsiveness than central venous pressure (AUC = 0.57) or pulmonary wedge pressure (AUC = 051). Of the 37 patients, 25 were in septic shock. The AUC for Δ(RESP)PP≥10% to predict responsiveness in patients with septic shock was 0.84 (sensitivity, 78%; specificity, 93%). CONCLUSION: The parameter Δ(RESP)PP has limited value in predicting fluid responsiveness in patients who are ventilated with low tidal volumes, but a Δ(RESP)PP>10% is a significant improvement over static parameters. A Δ(RESP)PP≥10% may be particularly useful for identifying responders in patients with septic shock.