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The degree of induced hypotension necessary to achieve a significant reduction in intraoperative blood loss has never been defined. Forty patients undergoing primary total hip arthroplasty during epidural anesthesia by a single surgeon were randomly assigned to have mean arterial pressure maintained at 50 ± 5 mm Hg or 60 ± 5 mm Hg throughout surgery. Intraoperative blood loss was 179 ± 73 mL in the 50 mm Hg group and 263 ± 2 98 mL in the 60 mm Hg group (P = 0.004). Subjectively, there was more bleeding during surgery in the 60 mm Hg group during dissection of the hip joint (P = 0.0026) and while reaming the acetabulum (P = 0.0001) and femur (P = 0.0001). No difference in transfusion requirements, postoperative hematocrit, or duration of surgery was noted. A difference in mean arterial blood pressure of 10 mm Hg from 50 to 60 mm Hg during surgery for total hip arthroplasty under epidural anesthesia has a measurable effect on intraoperative blood loss.