Intraoperative Goal-directed Fluid Management

Recent evidence suggests that goal-directed fluid management using stroke volume (blood ejected by the heart) is the most physiologic approach for fluid replacement. We propose to develop a body mass index (BMI)-specific fluid replacement formula based on stroke volume guidance. Arterial pulse pressure variation (dPP) induced by mechanical ventilation is a proposed predictor of fluid responsiveness as well. We will therefore also investigate if stroke volume (measured by esophageal Doppler monitoring) and pulse pressure variation comparably predict fluid responsiveness by simultaneously measuring both parameters. Adequate tissue oxygenation is essential to maintain normal physiologic functions. Fat tissue oxygenation is critically low in the obese surgical patient. It is likely that poor fat tissue oxygenation results in part from inadequate fluid replacement. We propose to determine if fat tissue oxygenation is comparable from lean to morbidly obese patients when fluid replacement is optimized. Individuals scheduled for elective, open abdominal surgeries, vaginal hysterectomies or genital prolapse repair will be assigned to six groups according to BMI, from lean to morbidly obese categories. The primary aim will be to develop a statistical equation for predicting fluid requirements as a function of BMI. A maximum of 100 patients will be able to detect an R-squared of 10% or more with 90% power at the 0.05 significance level, and will enable adequate estimation of the relationship of interest.