Abilities of pulse pressure variations and stroke volume variations to predict fluid responsiveness in prone position during scoliosis surgery

Background Pulse pressure variation (PPV) and stroke volume variation (SVV) are robust indicators of fluid responsiveness in mechanically ventilated supine patients. The aim of the study was to evaluate the ability of PPV and SVV to predict fluid responsiveness in mechanically ventilated patients in the prone position (PP) during scoliosis surgery. Methods Thirty subjects were studied after the induction of anaesthesia in the supine position [before and after volume expansion (VE) with 500 ml of hetastarch 6%] and in PP (immediately after PP and before and after VE). PPV, SVV, cardiac output (CO), and static compliance of the respiratory system were recorded at each interval. Subjects were defined as responders (Rs) to VE if CO increased ≥15%. Results Three subjects were excluded. In the supine position, 16 subjects were Rs. PPV and SVV before VE were correlated with VE-induced changes in CO ( r 2 =0.64, P r 2 =0.56, P 11% (sensitivity=88%, specificity=82%) and by SVV >9% (sensitivity=88%, specificity=91%). PP induced an increase in PPV and SVV ( P P r 2 =0.59, P r 2 =0.55, P 15% (sensitivity=100%, specificity=80%) and by SVV >14% (sensitivity=94%, specificity=80%). Conclusions PP induces a significant increase in PPV and SVV but does not alter their abilities to predict fluid responsiveness.