After abdominal surgery, a normal physiological ileus occurs. This type of ileus spontaneously resolves within 2-3 days after sigmoid motility returns to normal. However, the terms postoperative adynamic ileus or paralytic ileus are defined as ileus of the gut persisting for more than 3 days following surgery.1
Ileus occurs from hypomotility of the gastrointestinal tract in the absence of a mechanical bowel obstruction. This suggests that the muscle of the bowel wall is transiently impaired and fails to transport intestinal contents. This lack of coordinated propulsive action leads to the accumulation of both gas and fluids within the bowel. Although ileus has numerous causes, the postoperative state is the most common scenario for ileus development. Frequently, ileus occurs after intraperitoneal operations, but it may also occur after retroperitoneal and extra-abdominal surgery. The longest duration of ileus is noted to occur after colonic surgery.2, 3
The clinical consequences of postoperative ileus can be profound. Patients with ileus are immobilized, have discomfort and pain, and are at increased risk for pulmonary complications. Ileus also enhances catabolism because of poor nutrition. Overall, ileus prolongs hospital stays; according to a report by Livingston in 1990, it cost $750 million annually ($1500 per patient) in the United States.1 The main focus of this article is postoperative ileus.
According to some hypotheses, postoperative ileus is mediated via activation of inhibitory spinal reflex arcs. Anatomically, 3 distinct reflexes are involved: ultrashort reflexes confined to the bowel wall, short reflexes involving prevertebral ganglia, and long reflexes involving the spinal cord.3 The long reflexes are the most significant. Spinal anesthesia, abdominal sympathectomy, and nerve-cutting techniques have been demonstrated to either prevent or attenuate the development of ileus.4, 5
The surgical stress response leads to systemic generation of endocrine and inflammatory mediators that also promote the development of ileus. Rat models have shown that laparotomy, eventration, and bowel compression lead to increased numbers of macrophages, monocytes, dendritic cells, T cells, natural killer cells, and mast cells, as demonstrated by immunohistochemistry.6 Calcitonin gene–related peptide, nitric oxide, vasoactive intestinal peptide, and substance P function as inhibitory neurotransmitters in the bowel nervous system. Nitric oxide and vasoactive intestinal peptide inhibitors and substance P receptor antagonists have been demonstrated to improve gastrointestinal function.7, 8
Patients with ileus typically present with vague, mild abdominal pain and bloating. They may report nausea, vomiting, and poor appetite. Abdominal cramping is usually not present. Patients may or may not continue to pass flatus and stool.
Patients may have distended and tympanic abdomens, depending on the degree of abdominal and bowel distension. The abdomen may be tender. A distinguishing feature is absent or hypoactive bowel sounds unlike the high-pitched sound of obstruction. The silent abdomen of ileus reveals no discernible peristalsis or succussion splash.
Most cases of ileus occur after intra-abdominal operations. Normal resumption of bowel activity after abdominal surgery follows a known and predictable pattern.
The small bowel typically regains function within hours. The stomach regains activity in 1-2 days, and the colon regains activity in 3-5 days.9 Serial abdominal radiographs mapping the distribution of radiopaque markers have shown that the colonic gradient for resolution of postoperative ileus is proximal to distal. The return of propulsive activity to the right colon occurs earlier than to the transverse or left colon.10
Other causes of ileus are as follows:
Causes of adynamic ileus
Drugs (eg, opioids, antacids, coumarin, amitriptyline, chlorpromazine)
Metabolic (eg, low potassium, magnesium, or sodium levels; anemia; hyposmolality)
Trauma (eg, fractured ribs, fractured spine)
Biliary and renal colic
Head injury and neurosurgical procedures
Intra-abdominal inflammation and peritonitis