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.