Dynamic arterial elastance as a predictor of arterial pressure response to fluid administration: a validation study

Introduction: Functional assessment of arterial load by dynamic arterial elastance (Ea(dyn)), defined as the ratio between pulse pressure variation (PPV) and stroke volume variation (SVV), has recently been shown to predict the arterial pressure response to volume expansion (VE) in hypotensive, preload-dependent patients. However, because both SVV and PPV were obtained from pulse pressure analysis, a mathematical coupling factor could not be excluded. We therefore designed this study to confirm whether Ea(dyn), obtained from two independent signals, allows the prediction of arterial pressure response to VE in fluid-responsive patients. Methods: We analyzed the response of arterial pressure to an intravenous infusion of 500 ml of normal saline in 53 mechanically ventilated patients with acute circulatory failure and preserved preload dependence. Ea(dyn) was calculated as the simultaneous ratio between PPV (obtained from an arterial line) and SVV (obtained by esophageal Doppler imaging). A total of 80 fluid challenges were performed (median, 1.5 per patient; interquartile range, 1 to 2). Patients were classified according to the increase in mean arterial pressure (MAP) after fluid administration in pressure responders (>= 10%) and non-responders. Results: Thirty-three fluid challenges (41.2%) significantly increased MAP. At baseline, Ea(dyn) was higher in pressure responders (1.04 +/- 0.28 versus 0.60 +/- 0.14; P < 0.0001). Preinfusion Ea(dyn) was related to changes in MAP after fluid administration (R-2 = 0.60; P < 0.0001). At baseline, Ea(dyn) predicted the arterial pressure increase to volume expansion (area under the receiver operating characteristic curve, 0.94; 95% confidence interval (CI): 0.86 to 0.98; P < 0.0001). A preinfusion Eadyn value >= 0.73 (gray zone: 0.72 to 0.88) discriminated pressure responder patients with a sensitivity of 90.9% (95% CI: 75.6 to 98.1%) and a specificity of 91.5% (95% CI: 79.6 to 97.6%). Conclusions: Functional assessment of arterial load by Ea(dyn), obtained from two independent signals, enabled the prediction of arterial pressure response