Intestinal Pseudo-Obstruction (Ileus)

GENERAL PRINCIPLES

Definition

• Acute intestinal pseudo-obstruction or ileus consists of impaired transit of intestinal contents and obstructive symptoms (nausea, vomiting, abdominal distension, lack of bowel movements) without a mechanical explanation.

• Acute colonic pseudo-obstruction or Ogilvie syndrome describes massive colonic dilation without mechanical obstruction in the presence of a competent ileocecal valve, resulting from impaired colonic peristalsis.

• Chronic intestinal pseudo-obstruction is characterized by recurrent episodes of nausea, vomiting, and abdominal distention with bowel dilation without mechanical obstruction.⁸¹ An exact cause is often not found. One well-described etiology is a paraneoplastic phenomenon from antineuronal antibodies (anti-Hu), most often seen with small cell lung cancer.

Etiology

Ileus is frequently seen in the postoperative period. Narcotic analgesics administered for postoperative pain control may contribute, as can other medications that slow down intestinal peristalsis (calcium channel blockers, anticholinergic medications, TCAs, antihistamines). Other predisposing causes include virtually any medical insult, particularly life-threatening systemic diseases, infection, vascular insufficiency, and electrolyte abnormalities. Similar factors predispose to acute colonic pseudo­obstruction.

DIAGNOSIS

• A careful history and physical examination is essential in the initial evaluation.

• Conventional laboratory studies (CBC, complete metabolic profile, amylase, lipase) help in assessing for a primary intra-abdominal inflammatory process.

• Obstructive series (supine and upright abdominal radiograph with a CXR) determines the distribution of intestinal gas and assesses for the presence of free intraperitoneal air.

• Additional imaging studies assess for mechanical obstruction and inflammatory processes and include CT, contrast enema, and small bowel series.

TREATMENT

• Basic supportive measures consist of NPO, fluid replacement, and correction of electrolyte imbalances. Medications that slow down GI motility (adrenergic agonists, TCAs, sedatives, narcotic analgesics) should be withdrawn or dose reduced. The ambulatory patient is encouraged to remain active.

• Intermittent NG suction prevents swallowed air from passing distally. In protracted cases, gastric decompression, either using an NG tube or a percutaneous endoscopic gastrostomy (PEG) tube, vents upper GI secretions and decreases vomiting and gastric distension.

• Rectal tubes help decompress the distal colon; more proximal colonic distension may necessitate colonoscopic decompression, especially when the cecal diameter approaches 12 cm. This should be performed carefully with minimal air insufflation. Turning the patient from side to side may potentiate the benefit of colonoscopic decompression.

Medications

• Methylnaltrexone (Relistor, 8-12 mg SC per dose every other day) can be administered in settings where opioid medication use is contributing.

• Neostigmine (2 mg IV administered slowly over 3-5 minutes) is beneficial in selected patients with acute colonic distension. This can induce rapid reestablishment of colonic tone. It is contraindicated if mechanical obstruction has not been ruled out. Side effects include abdominal pain, excessive salivation, symptomatic bradycardia, and syncope. A trial of neostigmine may be warranted before colonoscopic decompression in patients without contraindications.⁸²

• Erythromycin (200 mg IV) acts as a motilin agonist and stimulates upper gut motility; it has been used with some success in refractory postoperative ileus.

• Alvimopan is a peripherally acting #956;-opioid receptor antagonist that enhances return of bowel function after abdominal surgery but has not been shown to shorten hospital stay.⁸³

• Mosapride citrate (15 mg PO tid), a 5-HT₄ receptor agonist, may reduce the duration of postoperative ileus when administered postoperatively.⁸⁴

• Prucalopride, also a selective 5-HT₄ agonist, can relieve symptoms in patients with chronic intestinal pseudo-obstruction.⁸⁵

Surgical Management

• Surgical consultation is required when the clinical picture is suggestive of mechanical obstruction or if peritoneal signs are present. Surgical exploration is reserved for acute cases with peritoneal signs, ischemic bowel, or other evidence of perforation.

• Cecostomy treats acute and chronic colonic distension when colonoscopic decompression fails.