Validation of pulse pressure variation and corrected flow time as predictors of fluid responsiveness in patients in the prone position

BackgroundThe aim of this prospective trial was to investigate the ability of pulse pressure variation (PPV) and corrected flow time (FTc) to predict fluid responsiveness in the prone position.MethodsForty-four patients undergoing lumbar spine surgery in the prone position on a Wilson frame were prospectively studied. PPV and FTc were measured before and after a colloid bolus (6 ml kg^-1) both in the supine and in the prone positions. Fluid responsiveness was defined as an increase in the stroke volume index of ≥10% as measured by oesophageal Doppler.ResultsIn the supine position, 26 patients were responders and the areas under the curve (AUC) of the receiver-operator characteristic (ROC) curves of PPV and FTc were 0.935 [95% confidence interval (CI): 0.870-0.999, P<0.001] and 0.822 (95% CI: 0.682-0.961, P<0.001), respectively. The optimal cut-off PPV and FTc values were 15% (sensitivity 73%, specificity 94%) and 358 ms (sensitivity 88%, specificity 78%), respectively. In the prone position, 34 patients were responders and the AUCs of PPV and FTc were 0.969 (95% CI: 0.912-1.000, P<0.001) and 0.846 (95% CI: 0.706-0.985, P=0.001), respectively. The optimal cut-off PPV and FTc values were 14% (sensitivity 97%, specificity 90%) and 331 ms (sensitivity 77%, specificity 90%), respectively.ConclusionsWhile the predictability of PPV was significantly higher than that of FTc in the prone position, both variables showed high predictability and remained as useful indices for guiding fluid therapy in prone patients with minimal alterations in their optimal cut-off values to predict fluid responsiveness.