Pulse Pressure Variation: Don't Throw the Baby Out with the Bathwater

摘要

To the Editor: We read with interest the study by Vignon and colleagues (1) [this issue, pp. 1022-1032] and congratulate the authors for comparing echocardiographic indices of fluid responsiveness in a large cohort of mechanically ventilated patients with acute circulatory failure. However, we are concerned that the results of this study may mislead one to conclude that the pulse pressure variation (ΔPP), with the area under the receiver operating characteristic (ROC) curve of 0.675, is of limited clinical value. Sixty-six percent of the patients were ventilated using low V_T, which is a well-known limitation of ΔPP to predict fluid responsiveness. We have recently described a novel test (2), the "tidal volume challenge," to improve the reliability of ΔPP during low-V_T ventilation. The test involves transiently increasing V_T from 6 ml/kg predicted body weight (PBW) to 8 ml/kg PBW for 1 minute and observing the change in ΔPP. The V_T is then reduced back to 6 ml/kg PBW. An increase in the absolute value of ΔPP of 3.5% or greater reliably predicts fluid responsiveness (sensitivity, 94%; specificity, 100%). This test can be easily performed using ΔPP recorded from a bedside monitor, without requiring cardiac output monitoring. If the "tidal volume challenge" had been applied to the 66% patients receiving low-V_T ventilation in this study (1), ΔPP would probably have been more reliable in predicting fluid responsiveness. Surprisingly, ΔPP and the dynamic echocardiographic parameters failed to have a greater diagnostic accuracy even in those patients who received a V_T 8 ml/kg or greater (Table E5 in Vignon and colleagues' online supplement) (1). None of the previous studies (3) have found such poor results at V_T ≥ 8 ml/kg.