Pulse pressure variations adjusted by alveolar driving pressure to assess fluid responsiveness

To evaluate the ability of DeltaPP/DeltaP [pulse pressure variations (DeltaPP) adjusted by alveolar pressure variations (DeltaP = Pplat-PEEPtot)] in predicting fluid responsiveness, to compare its accuracy to that of DeltaPP used alone and to evaluate the influence of tidal volume (Vt) on these two indices.

Prospective study.

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.

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. DeltaPP/DeltaP and DeltaPP were both higher in responders than in nonresponders. DeltaPP/DeltaP was a better predictor of fluid responsiveness than PP, especially for patients ventilated with Vt > or = 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 DeltaPP/DeltaP higher than 0.9 predicted fluid response with positive predictive value of 87% and negative predictive value of 78%. Overall DeltaPP and DeltaPP/DeltaP 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 DeltaPP for patients ventilated with Vt > or = 8 ml/kg. However, correcting DeltaPP by DeltaP still fails to predict fluid response reliably in patients ventilated with low tidal volume.