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Obstruction and Ileus of the Small Intestine
Intestinal obstruction occurs when the onward passage of intestinal contents is limited by mechanical abnormalities or a functional disturbance ( Fig. 59.1 ). Peristaltic activity may be abolished by reflexes originating from diseased structures within, or remote from, the abdominal cavity. When obstructive lesions occur, some motility may persist. The obstruction may be partial or complete, and when it occurs with vascular compromise, it may indicate simple ischemia or may be attributed to strangulation.
Obstruction and Adynamic Ileus of the Small Intestine.
The most common cause of small intestinal obstruction is adhesions (>50%). Herniation accounts for approximately 25% of obstructions. Adhesions are extrinsic, as are hernias, and other causes of extrinsic lesions may be congenital bands, volvulus, or carcinomatosis outside the bowel wall. The remaining 25% of small bowel obstructions are caused by inflammatory lesions, intussusceptions, neoplasms, foreign bodies, or atresias and stenosis. These lesions are primarily intrinsic to the bowel.
Ileus occurs when the bowel ceases to pass its contents, becoming adynamic. Ileus usually occurs after surgery but also results from inflammatory, metabolic, and neurogenic lesions. It also may be associated with electrolyte imbalances or drug administration. Acute inflammation in the bowel, such as appendicitis, diverticulitis, or peritonitis, can cause loss of motility and ileus. Ileus is also associated with acute pancreatitis, ischemic lesions of the bowel, and, occasionally, chest lesions causing systemic sepsis. Any of the hernias described in Section III can cause intestinal obstruction and manifest acutely.
Clinical Picture
Depending on the cause, acute obstruction of the bowel may present with abdominal pain, nausea, and vomiting of reflux origin. Abdominal examination reveals increased peristalsis, which gives way to alternating periods of hyperactivity and quiescence until the latter predominates.
In adynamic ileus, peristalsis ceases from the start; therefore the bowel is extremely quiet and emits poor bowel sounds. However, invariably there is increased fluid secretion into the gut and accumulation of gas, with the bowel becoming more and more distended. In patients with mechanical ileus, the distention is proximal to the point of obstruction, whereas in patients with reflex ileus, the distention is more generalized.
As peristalsis fails, the absorptive functions also fail, permeability is altered, and intestinal bacteria and toxic substances can translocate. Water and electrolytes enter the bowel lumen, aggravating the distention and invariably increasing the vomiting. The overall effect on the patient is dehydration of body tissue and circulatory failure. Patients may become hypotensive and may experience shock and sepsis.
In mild intermittent obstruction, the symptoms are less severe and the only clinical presentation may be recurrent abdominal pain. However, anorexia always correlates with the pain and recurrent bloating of abdominal distention. When obstruction is complete, bowel movements cease. With partial obstruction, the patient may have some bowel movement or even mild diarrhea.
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