Mechanisms of postoperative ileus

Abstract

Postoperative ileus is an iatrogenic condition that follows abdominal surgery. Three main mechanisms are involved in its causation, namely neurogenic, inflammatory and pharmacological mechanisms. In the acute postoperative phase, mainly spinal and supraspinal adrenergic and non-adrenergic pathways are activated. Recent studies, however, show that the prolonged phase of postoperative ileus is caused by an enteric molecular inflammatory response and the subsequent recruitment of leucocytes into the muscularis of the intestinal segments manipulated during surgery. This inflammation impairs local neuromuscular function and activates neurogenic inhibitory pathways, inhibiting motility of the entire gastrointestinal tract. The mechanisms underlying the recruitment of the inflammatory cells, and their interaction with the intestinal afferent innervation, are discussed. Finally, opioids administered for postoperative pain control also contribute to a large extent to the reduction in propulsive gastrointestinal motility observed after abdominal surgery.

Peripheral opioid antagonism

“…This may follow both acute or chronic opioid intake. Acutely, it usually manifests as a part of a postoperative ileus that itself may be attributed to surgical stress, or to alterations in fluid and electrolyte balance [1]. In patients with chronic usage of opioids, the bowel dysfunction may manifest as a range of symptoms with more than half of patients experiencing constipation.…”

Complication avoidance and management in anterior lumbar interbody fusion

“…The importance of each of these contributing mechanisms may vary during the time course of POI, although there is considerable overlap. 33 Neuronal mechanisms appear to play the most significant role early after abdominal surgery. However, there are clearly other important mechanisms because POI often does not resolve for several days.…”

“…3,33 More intense stimuli, such as handling of the intestine, trigger an additional high-threshold supraspinal (autonomic) pathway. 33 Catecholamines play an important role in the early phases of POI; however, plasma and tissue levels normalize long before the return of bowel activity.…”

“…6 During abdominal surgery, activation of inhibitory reflexes originates from the incision (somatic fibers) and from manipulation of the intestines (visceral fibers). 17,33 The activation of neural pathways during abdominal surgery depends on the intensity of the nociceptive stimulus applied and the part of the intestine evaluated.…”

In vitro effects of bethanechol on specimens of intestinal smooth muscle obtained from the duodenum and jejunum of healthy dairy cows

“…24 In contrast to findings in horses, spontaneous paralytic (adynamic) ileus is more common in cattle than is postoperative paralytic ileus. 6,24 Although the factors involved in the pathogenesis of postoperative ileus include inflammatory, metabolic, hormonal, neurogenic, and vascular mechanisms, 25 spontaneous paralytic ileus in cattle is mainly attributable to metabolic disturbances and electrolyte imbalances, such as hypocalcemia or hypokaliemia, 6,26 but sympathetic hyperactivity may also be involved. 24 The duodenum also plays a pivotal role in abomasal emptying in ruminants; hence, motility disorders of the duodenum may result in incomplete abomasal emptying.…”