Intestinal obstruction accounts for 20% of surgical admissions. Conditions leading to intestinal obstruction are classified according to the relationship between the obstructing agent and the intestinal wall (Table 86-1). The obstruction can be extraluminal (surgical adhesions from prior surgery and neoplastic disease), intraluminal (strictures and abdominal ileus), intramural (inflammatory bowel disease, e.g., Crohn’s), complex (vascular causes, e.g., strangulation), or closed loop obstruction (e.g., volvulus, where both proximal and distal obstruction of the loop of bowel is present).
TABLE 86-1Common Causes of Intestinal Obstruction ||Download (.pdf) TABLE 86-1 Common Causes of Intestinal Obstruction
Metastatic small bowel cancer
Local tumor invasion
External causes (inguinal/femoral)
Internal (past roux-en-y bypass)
Radiation induced strictures
Post ischemic strictures
Congenital abnormalities (webs, duplications, malrotations)
In most cases, the obstruction is localized in the small intestine and results from adhesions. Less common causes include hernias with strangulation, malignancy (cholangiocarcinoma and pancreatic cancer), inflammation, endometriosis, volvulus, foreign body, and the use of nonsteroidal anti-inflammatory drugs. Large bowel obstruction is less common and result from tumor involvement (colon and ovarian cancer), diverticulitis, or volvulus. Mortality rates range from 5% to 10% when the obstruction is caused by adhesions and 15%–20% when due to cancer, gangrene, or when localized in the large bowel. Mortality also increases in the presence of malnutrition and hypoalbuminemia. Perioperative risks increase in cases of delayed treatment, high obstruction, strangulation with tissue necrosis, sepsis, cardiovascular instability, extreme of age, multiple comorbidities, and poor nutritional status.
Hemodynamic instability is the result of both hypovolemia, due to fluid sequestration, profuse vomiting (or stomach suction), and decreased venous return. The intestine reabsorbs 6–9 L of fluids on a daily basis, secreting only 400 mL. In the case of obstruction, fluids accumulate in the bowel and lead to intravascular volume depletion. Vomiting usually begins when 3 L is sequestered, while hypotension, tachycardia, and oliguria occur with ≥6 L. Distention of the intestine compresses the inferior vena cava and upwardly displaces the diaphragm. The resulting increase in intrathoracic pressure is associated with a decrease in venous return which may aggravate the hypotension and tachycardia. Gastric decompression or profuse vomiting can contribute to further fluid loss. Renal injury, shock, and death can result.
Proximal obstruction is characterized by hypokalemic hypochloremic acidosis, with a gradual decrease in sodium and chloride. Hyponatremia aggravates hypotension and causes mental status changes. Hypokalemia will cause ECG changes including alterations in the ST segment as well as dysrhythmias. Metabolic acidosis results from dehydration, starvation, ketoacidosis and loss of alkali, as well as severe tissue hypoperfusion or hypovolemia. Metabolic alkalosis ...