Pulse pressure variations adjusted by alveolar driving pressure to assess fluid responsiveness
To evaluate the ability of ∆PP/∆P [pulse pressure variations (∆PP) adjusted by alveolar pressure variations (∆P = Pplat-PEEPtot)] in predicting fluid responsiveness, to compare its accuracy to that of ∆PP used alone and to evaluate the influence of tidal volume (Vt) on these two indices.
A 22-bed general intensive care unit (ICU).
Eighty-four surgical or medical ventilated patients requiring fluid challenge.
A 6 ml/kg colloid fluid challenge in 30 min.
Measurements and results
Hemodynamic measurements taken before and after fluid challenge. Patients separated into responders and nonresponders according to a 15% increase in their cardiac output. Thirty-nine patients found to be responders and 45 nonresponders. ∆PP/∆P and ∆PP were both higher in responders than in nonresponders. ∆PP/∆P was a better predictor of fluid responsiveness than ∆PP, especially for patients ventilated with Vt ≥ 8 ml/kg [area under the curve (AUC) 0.88 (0.77–0.98) versus 0.75 (0.60–0.89), P < 0.01)]. In this population ∆PP/∆P higher than 0.9 predicted fluid response with positive predictive value of 87% and negative predictive value of 78%. Overall ∆PP and ∆PP/∆P reliability was poor for patients ventilated with Vt < 8 ml/kg [AUC 0.63 (0.45–0.81) and 0.72 (0.55–0.88), respectively].
In this mixed ICU population ∆PP adjusted by ∆P is a simple index which outperforms ∆PP for patients ventilated with Vt ≥ 8 ml/kg. However, correcting ∆PP by ∆P still fails to predict fluid response reliably in patients ventilated with low tidal volume.
KeywordsFluid responsiveness Delta PP Positive respiratory pressure ARDS
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