Comparison(s): Intervention versus control group. Patients assigned to the intervention rSO2-monitored group will be managed with conservative measures designed to maintain the rSO2 value at, or above, its preoperative value. Such measures include increases in pump flow, blood pressure, anesthetic dose, arterial oxygen tension, carbon dioxide tension, and hematocrit. Those patients in the control group will be managed according to current established practice. Although rSO2 is also recorded in this group, the monitor's readings are blinded.