Predictor of fluid responsiveness in the 'grey zone': Augmented pulse pressure variation through a temporary increase in tidal volume

Background: Pulse pressure variation (PPV) is widely used as a predictor of fluid responsiveness. However, a previous study has suggested a 'grey zone' between 9 and 13% in which PPV would be inconclusive to predict fluid responsiveness. Considering PPV is based on cardiopulmonary interactions, we evaluated whether an augmented PPV using a temporary increase in tidal volume (V T) from 8 to 12 ml kg^-1 has the predictability for fluid responsiveness in patients within the grey zone. Methods: Adult patients requiring general anaesthesia were enrolled. During the period when PPV was within the range of 9-13%, haemodynamic variables such as stroke volume index (SVI) and PPV with an 8 ml kg^-1 tidal volume ventilation (PPV8) were obtained before and after volume expansion (6 ml kg^-1) under mechanical ventilation. Augmented PPV induced by 2-min ventilation with a V T of 12 ml kg^-1 (PPV12) was also recorded immediately before volume loading. The patients whose SVI increased ≥10% after volume expansion were considered responders. Results: In 38 enrolled patients, 20 were responders. Receiver operating characteristic curve analysis showed PPV12 had an excellent predictability for fluid responsiveness {area under the curve [AUC]=0.935 [95% confidence interval (CI) 0.805-0.989]; sensitivity 95%; specificity 72%; P<0.0001}. The optimal threshold for PPV12 was >17%. However, PPV8 failed to show significant predictability [AUC=0.668 (95% CI 0.497-0.812); sensitivity 65%; specificity 61%; P=0.06]. Conclusion: In mechanically ventilated patients, our augmented PPV successfully predicted fluid responsiveness in the previously suggested grey zone. Clinical trial registration: ClinicalTrials.gov, NCT02653469.