Comparison of arterial systolic pressure variation with other clinical parameters to predict the response to fluid challenges during cardiac surgery.

Prophylactic optimization of stroke volume during surgery has been thought by some to reduce complications following surgery. Mechanical ventilation has been shown to induce variations in systolic systemic arterial blood pressure. Measuring such variations in systolic pressure (SPV) might serve as an attractive method for guiding fluid therapy intraoperatively. It is unknown if variations in systolic pressure following the rapid intravenous administration of a specific volume of fluid would lead to changes in pressure measurements obtained from a pulmonary artery with sufficient sensitivity to predict or guide the need for expansion of the intravascular volume to optimize stroke volume as an index of cardiac function. The purpose of this study was to determine if such measurements of changes in systolic pressures would be useful in optimizing stroke volume. Nineteen patients undergoing cardiac surgery were enrolled in a prospective cohort study. Following induction of general anesthesia, one or more 250 mL boluses of 6% hetastarch were administered. Stroke volume was calculated from the cardiac output obtained by thermodilution using a pulmonary artery catheter. If the patient s stroke volume increased by less than 10% as a result of a given fluid challenge, the patient was classified as a non-responder. However, if the stroke volume increased by more than 10%, the patient was classified as a responder. The variations in systolic pressure and echocardiographic indices were simultaneously measured before and after the administration of each 250 mL fluid bolus. Pulmonary artery occlusion pressure (PAOP) values were significantly lower in patients who responded to fluid boluses (p=0.0085) than in those who did not. Similarly SPV and SPVdown values (defined as the decrease in systolic pressure with ventilation) were significantly greater in the responders (p<0.05). No significant intergroup differences were observed in SPVup (increase in systolic pressure with ventilation) or echocardiographic-derived left ventricular end diastolic area. A PAOP value less than 10 mm Hg predicted a response (sensitivity 68%, specificity 79%). Although significant intergroup differences in the extent of systolic pressure variations were observed, no appropriate threshold values could be determined that would accurately predict the response to a fluid bolus. There is a relationship between SPV and SPVdown values and intravascular volume status. SPV and echocardiographic-derived values did not predict the response to a fluid bolus as well as values obtained from the pulmonary artery catheter.