Ileus
Basic Information 
Epidemiology
Risk Factors
• Intestinal surgery: Postoperative ileus occurs predominantly after surgical correction of lesions involving the small intestine. Postoperative ileus may also be seen after correction of ascending colon lesions, primarily large colon volvulus. Traumatic handling of the intestine, intestinal distension, resection and anastomosis, and intestinal ischemia may contribute to ileus in these cases.
• Other conditions that have been associated with ileus include:
• Risk factors for postoperative ileus identified in one equine retrospective study were age older than 10 years, Arabian breed, packed cell volume (PCV) above 45%, high serum concentrations of protein and albumin, anesthesia longer than 2.5 hours, surgery longer than 2 hours, resection and anastomosis, and lesions in the small intestine. Performing a pelvic flexure enterotomy decreased the risk of postoperative ileus in this study.
• In another report PCV above 48%, high heart rate, elevated serum glucose, small intestinal lesions, and ischemic small intestine were identified as risk factors. The incidence of postoperative ileus in horses undergoing surgical treatment of colic has been reported to be between 21% and 18.4%.
Clinical Presentation
Etiology and Pathophysiology
• The muscle layers in the intestinal tract responsible for gross motility are contained in the muscularis externa layer, which is divided into an inner circular muscle and an outer longitudinal muscle and separated by the myenteric plexus. Coordination of activity of both of these muscle layers is necessary for normal progressive motility. Coordination of smooth muscle cell activity occurs at four levels:
GI smooth muscle cells demonstrate continual oscillations in membrane potential that initiate contractile activity.
• The precise cause of ileus is unknown, although evidence suggests that inflammation may play a central role.
