Recent technology allows the measurement of patients' total blood volume with 98% accuracy within 90 minutes or less. This is key to understanding the effect of hypotensive anesthesia on patients undergoing total hip arthroplasty. The drop in blood pressure enhances the dilutional effect of intravenous fluid given during the procedure. Increases in TBV could result in decreases of postoperative hemoglobin. Understanding the effect of hypotensive anesthesia on postoperative hemoglobin levels and TBV will enhance our understanding of postoperative blood management and transfusion triggers.