Pulse pressure variation : driving airway pressure ratio to predict fluid responsiveness in mechanically-ventilated patients

Introduction: Accuracy of Pulse Pressure Variation (PPV) in predicting fluid responsiveness during mechanical ventilation is higher when tidal volume is ≥8ml/kg [Michard, 2005] but lower when tidal volume is <8 ml/kg [De Backer, 2005] of predicted body weight (PBW) possibly because small tidal volumes induce only minimal changes in intra-thoracic pressure, cardiac preload and afterload. Objective: The aim of this study was to evaluate whether PPV divided by Driving (the difference between end-inspiratory and end-expiratory) Airway Pressure (Paw) accurately predicts fluid responsiveness during mechanical ventilation with tidal volume between 6 and 10 ml/kg PBW. Methods: Nineteen critically ill patients ventilated with tidal volume between 6 and 10 ml/kg PBW were enrolled. PPV and Paw were recorded before a fluid challenge. Patients with an increase in stroke volume ≥15% across the fluid challenge were classified as “responders”. Results: Six patients were “responders”. PPV/Paw was significantly higher in responders than in non-responders (1,3 [0,9-1,8] vs. 0,7 [0,4-0,8]; p 0,003). PPV/Paw >0.9 predicted fluid responsiveness with sensibility 83%, specificity 100%, positive predictive value 100% and negative predictive value 93%. Figure 1. Receiver-operating characteristic (ROC) curve of PPV/Paw. Area under ROC curve was 0,94 denoting very high diagnostic accuracy. Conclusions: PPV/Paw accurately predicts fluid responsiveness during mechanical ventilation with tidal volume between 6 and 10 ml/kg PBW.