Etiology of Ileus The most common cause of ileus is Abdominal surgery Other causes include Intraperitoneal or retroperitoneal inflammation (eg, appendicitis, diverticulitis, perforated duodenal ulcer) Retroperitoneal or intra-abdominal hematomas (eg, from ruptured abdominal aortic aneurysm, blunt abdominal trauma) Metabolic disturbances (eg, hypokalemia) Medications (eg, opioids, anticholinergics, sometimes calcium channel blockers) Sometimes renal or thoracic disease (eg, lower rib fractures, lower lobe pneumonias, myocardial infarction) Gastric and colonic motility disturbances after abdominal surgery are common.