Mr. J. is a 55-year-old African American man who was admitted 72 hours ago to a general surgical unit after surgery for a bowel obstruction. The surgical procedure involved extensive abdominal surgery to repair a perforated colon, irrigate the abdominal cavity, and provide hemostasis. During surgery his systolic blood pressure dropped to 70 mm Hg. Seven units of packed red blood cells and 4 L of normal saline were administered intravenously to restore blood loss and circulating volume. He is receiving 60% O2 through an aerosol face mask. He is being monitored with a cardiac monitor and pulse oximeter. He has a central intravenous catheter in place and is receiving 0.9% normal saline IV at 125 ml per hour. A urinary catheter is in place.