The purpose of this study is to determine whether Hemospan is superior to Voluven for treatment of hypotensive episodes during the perioperative period (from induction of spinal anesthesia until 6 hours after skin closure), and for reducing the incidence of operative and postoperative complications including organ dysfunction and failure until follow-up at one month following surgery. An independent Data Safety Monitoring Board (DSMB) will periodically evaluate the safety data collected during this trial