This patient has a mechanical small-bowel obstruction (SBO).  Vomiting caused hypokalemia and, along with decreased oral intake, resulted in dehydration and orthostasis in this patient.  SBO is further categorized by anatomic location (ie, proximal versus mid/distal) or simple versus strangulated.  Complete proximal obstructions are characterized by early vomiting, abdominal discomfort, and abnormal contrast filling on x-ray.  Mid or distal obstructions typically present as colicky abdominal pain, delayed vomiting, prominent abdominal distension, constipation-obstipation, hyperactive bowel sounds, and dilated loops of bowel on abdominal x-ray.  Simple obstruction refers to luminal occlusion; strangulation refers to loss of blood supply to the bowel wall.  Patients with strangulated obstructions may have peritoneal signs (eg, rigidity, rebound) and signs of shock; fever, tachycardia, and leukocytosis are late findings.  This patient most likely has a simple mid or distal SBO.

Adhesions are by far the most common cause of SBO.  They may be congenital in children (eg, Ladd's bands), but typically result from abdominal operations or inflammatory processes.  This adult patient with an SBO is likely to have had abdominal surgery, such as an appendectomy.

(Choice B)  Ingestion of fatty foods precipitates biliary colic and acute cholecystitis, which usually cause right upper-quadrant abdominal pain.  Acute cholecystitis is accompanied by fever, leukocytosis, and occasionally abnormal liver function tests.

(Choice C)  High alcohol consumption can be associated with acute pancreatitis or alcoholic hepatitis.  Pancreatitis can cause an ileus (decreased bowel sounds) and a tympanic abdominal examination.  However, an aspartate aminotransferase/alanine aminotransferase ratio >2 is typically seen if the patient is a heavy drinker.  In addition, abdominal pain in pancreatitis is usually epigastric, constant, and radiates to the back.

(Choice D)  Occasional black or tarry stools (ie, melena) are suggestive of a gastrointestinal bleed originating above the ligament of Treitz.  The most common causes of melena in a man of the patient's age are peptic ulcer disease, gastritis, esophagitis, and Mallory-Weiss tear.  Peptic ulcer disease is a rare cause of proximal but not mid-distal SBO.  The other etiologies are not associated with bowel obstruction.

(Choice E)  Recent fever and nonbloody diarrhea would be concerning for Crohn disease in a man this age.  Crohn disease can cause SBO; however, Crohn-related SBO usually results from chronic fibrosis late rather than early in the course of the disease.  Moreover, postoperative SBO is much more common than SBO from an inflammatory bowel disorder.

(Choice F)  Recent weight loss can predispose patients to superior mesenteric artery syndrome or be a sign of neoplasm, endocrine disorder, or inflammatory condition.  Although these conditions can cause SBO, they are much less common than postoperative adhesions, especially in younger patients.

Educational objective:
Complete small-bowel obstruction usually presents with nausea, vomiting, abdominal bloating, and dilated loops of bowel on abdominal x-ray.  Adhesions, typically postoperative, are the most common etiology.