A previously healthy 65-year-old female underwent an emergent sigmoid colectomy and proximal colostomy for perforated diverticulitis. Intraoperatively, the patient was found to have extensive fecal contamination of the peritoneal cavity with minimal blood loss. She received two liters of intravenous fluids during the operation. Twelve hours after surgery, the patient is found to have a blood pressure of 110/60 mmHg (supine), heart rate of 110/min, temperature of 37.8 °C, and respiratory rate of 14/min. Her mucous membranes appear dry, and skin turgor is decreased. She does not have jugular venous distention. Cardiac and respiratory exams are unremarkable. The patient is noted to have only produced 30 cc of dark yellow urine in the last 3 h. Postoperative laboratory values demonstrate a rising BUN of 34 mg/dl (normal 7–21 mg/dl) and a creatinine of 1.5 mg/dl (0.5–1.4 mg/dl) (preoperative creatinine 0.8 mg/dl). Hemoglobin and hematocrit are the same as preoperative at 11 g/dl (12–15.2 g/dl) and 33% (37–46%).