A 62-year-old woman with worsening mid-abdominal pain, bloating, obstipation, nausea, and bilious vomiting presents to the emergency department. Her past surgical history is significant for a total abdominal hysterectomy 8 years ago. She is afebrile, but tachycardic to 110 bpm. Her abdomen is distended and tympanic to percussion, without rebound, guarding, or rigidity. There are hyperactive, tinkling bowel sounds with no external hernias. White blood cell count is 8000/uL.
Small-bowel obstruction (SBO), or interruption of the flow of intestinal contents, is common, accounting for 12% to 16% of all surgical admissions.1,2 Over 300,000 operations are performed annually for SBO, and resultant costs exceed $2 billion each year in the United States.3
The most common causes of SBO in the United States are adhesions (70%), followed by malignancy, inflammatory strictures, and incarcerated hernias. Other less common causes of SBO include congenital lesions, volvulus, intussusception, and gallstone ileus.4
When intestinal contents cannot pass normally, the bowel proximal to the site of obstruction becomes dilated, while contents distally are able to pass. Bacterial overgrowth occurs when intestinal contents become static, leading to increased distention, bowel wall edema, loss of absorptive function of the bowel, fluid sequestration, dehydration, and electrolyte abnormalities. In addition, fluid can be secreted into the bowel lumen, and transudative loss of fluid into the peritoneum can occur, worsening dehydration. Dehydration leads to decreased urine output, azotemia, hypotension, and tachycardia. Emesis contributes to electrolyte and acid loss, resulting in the classic hypokalemic, hypochloremic metabolic alkalosis. Strangulation occurs when intraluminal pressure exceeds perfusion pressure, causing ischemia and even necrosis of the bowel wall.
SBO can be classified as complete or partial. Most cases of strangulated bowel are in the setting of complete obstruction, but a Richter’s hernia (Figure 9–1) is a special case in which one wall of the bowel is strangulated, resulting in ischemia of a portion of the bowel without complete obstruction. As these patients do not present with clinically significant obstruction, diagnosis is often delayed, increasing morbidity. A “closed-loop” obstruction occurs when a portion of the bowel is twisted and thus consists of two points of obstruction. In these cases, the intestinal contents have no proximal or distal outlet. These obstructions are at high risk for progression to ischemia and necrosis.
Abdominal CT scan depicting a Richter’s hernia. The anterior wall of the colon protrudes through a ventral hernia defect (arrow). As the proximal colonic caliber is normal, there is no high-grade obstruction, but free fluid in the paracolic gutters (asterisks) raises concern for possible ischemia.
Presentation of SBO depends of the site of obstruction, whether the obstruction is partial or ...