Ileus

Chapter 40


Ileus



Ileus, an inhibition of gastrointestinal motility, commonly occurs in patients in the intensive care unit (ICU). Ileus can be a physiologic response—for example, after abdominal surgery—or it may be pathologic. The presence of ileus may be associated with significant morbidity because it restricts patients from normal use of their gastrointestinal tract. Because of its high prevalence and potentially adverse effects, the recognition and management of ileus are important in the care of patients in the ICU.


Ileus (also called adynamic ileus) is defined as the functional inhibition of propulsive bowel activity, irrespective of pathogenic mechanism. This differs from other gastrointestinal motility disorders resulting from structural abnormalities—for example, small bowel obstruction. Postoperative ileus is the uncomplicated ileus that follows surgery and usually resolves spontaneously within 2 to 3 days. Prolonged postoperative ileus lasts longer than 3 days. Ileus of the colon with sudden massive dilatation is called acute colonic pseudo-obstruction or Ogilvie syndrome. Toxic megacolon is another form of colonic ileus in which inflammation involves all colonic tissue layers and that results in systemic toxicity.



Pathophysiology


A multitude of pathologic phenomena are associated with the presence of an ileus. Inflammation (either postoperative or systemic) predisposes to ileus. An impairment of intestinal blood flow (arterial or venous) can lead to an ileus. Conversely, the presence of a simple ileus itself does not lead to the impairment of intestinal blood flow. Analogous to that which occurs in states of mechanical bowel obstruction, a change in bowel flora may also occur during ileus. This can lead to stasis, overgrowth of bacteria, and subsequent malabsorption. There may also be a change in the bowel contents similar to that which occurs in distended loops of bowel during intestinal obstruction. Under these circumstances, fluid inside the bowel lumen increases because of intestinal secretion plus a failure of absorption. Intestinal gas also contributes to the abdominal distention, and the gas-filled loops of intestine are routinely seen on the abdominal radiograph of a patient with ileus. In the case of ileus, this gas results primarily from swallowed air.


Significant changes in motility occur in both the small and large intestine in the presence of ileus. Unfortunately, the mediators of these changes have not yet been identified, even in postoperative ileus (although several neurohormonal peptides have been studied as potential candidates). Although it has been suggested that adrenergic mediation is responsible, this does not explain why the ileus persists for several days. Also, evidence suggests that mechanisms other than spinal reflexes play a role because the use of nonopioid epidural anesthesia (which blocks efferent sympathetic nerves) does not shorten the duration of ileus. Although damage to cholinergic nerves from hypoxemia or from surgical manipulation could explain some cases of ileus, activation of the nonadrenergic, noncholinergic inhibitory nerves is the most likely cause for most cases of ileus.



Causes of Ileus in the Intensive Care Unit


Common intra-abdominal and extra-abdominal causes of ileus that would be relevant for patients in the ICU are listed in Boxes 40.1 and 40.2. Likewise, intra-abdominal and extra-abdominal conditions associated with acute colonic pseudo-obstruction or Ogilvie syndrome (a nonobstructive, acute massive dilatation of the colon that is temporary and reversible) are listed in Boxes 40.3 and 40.4.



BOX 40.1   Intra-abdominal Causes of Ileus







BOX 40.2   Extra-abdominal Causes of Ileus

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Jul 7, 2016 | Posted by in CRITICAL CARE | Comments Off on Ileus

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