A 38-year-old woman presents to the emergency department with colicky abdominal pain, nausea, and vomiting for the past day. She has had at least ten episodes of green, bilious emesis without blood. She has had no passage of stool or flatus per rectum since yesterday morning and has not eaten in 24 h due to the vomiting and abdominal pain. She denies a history of similar symptoms and has no other medical problems. Past surgical history is significant for a cesarean section 2 years ago. Her temperature is 37.8 °C, heart rate is 122/min, blood pressure is 124/78 mmHg, and respiratory rate is 14/min. Her mucous membranes are dry, and her abdomen is distended, with a well-healed low transverse abdominal incision. Auscultation reveals high-pitched tinkling bowel sounds. She has mild tenderness throughout the abdomen, but there is no rebound, guarding, or rigidity. No masses or hernias are identified. Rectal examination reveals normal tone, no gross blood, no masses, and no stool in the rectal vault. Laboratory examination reveals a white blood cell count of 8.2 × 103/μL (normal 4.1–10.9 × 103/μL), hemoglobin 17 g/dL (12.3–15.7 g/dL), hematocrit 51% (37–46%), sodium 141 mEq/L (135–145 mEq/L), potassium 2.9 mEq/L (3.5–5.0 mEq/L), chloride 93 mmol/L (98–106 mEq/L), bicarbonate 34 mEq/L (24–30 mEq/L), BUN 36 mg/dL (7–22 mg/dL), and creatinine 1.2 mg/dL (0.56–1.0 mg/dL). Urinalysis demonstrates aciduria. Beta-HCG is negative. An abdominal X-ray is provided in Fig. 3.1.