The value of pulse pressure variation to predict volume response in patients ventilated with low VT

Introduction

The prediction value of pulse pressure variation (ΔPP) in patients ventilated with low VT is not well studied. A ΔPP of 12 to 13% is validated as a predictor of volume response in several studies, but in patients ventilated with VT >8 ml/kg. One study has shown that the ΔPP of 12 to 13% does not predict volume response in patients ventilated with a low VT. We hypothesized that a lower cut-off value for ΔPP can predict volume response in patients with low VT.

Methods

Thirty-seven adult patients mechanically ventilated with a tidal volume <8 ml/kg (PBW), without cardiac arrhythmias, with a pulmonary artery catheter and a peripheral arterial catheter were included. An increase in cardiac index (thermodilution)) >15% output after a fluid challenge (Crystalloid 1,000 ml or Colloid 500 ml) was considered a positive response.

Results

Seventeen patients were responders. The ROC curve showed that the best cut-off value for ΔPP was 10% (ROC area = 0.74, 95% CI: 0.51 to 0.9; sensitivity 53%, specificity 95%, positive likelihood ratio 9.4 and negative 0.34). Twelve patients consisted of a heterogeneous group of patients (liver transplant, acute pancreatitis, aortic surgery). Among 25 septic shock patients, a ΔPP >10% showed a ROC area of 0.84 (sensitivity 78%, specificity 93%). In any case, the greater ΔPP, the greater the fluid response. ΔPP >10% was a better predictor than CVP or PAOP.

Conclusions

ΔPP has a limited value in patients ventilated with low VT. However, a ΔPP >10% may help identify septic shock patients that will respond to a fluid challenge.