Abdominal distension is the key clinical feature in intestinal pseudo-obstruction occurring in about 80% of cases.[1] Nausea, vomiting, early satiety, constipation, and generalized abdominal pain can also be observed.[12] These symptoms can be acute, chronic, or recurrent. Patients may also exhibit symptoms from a neuromuscular disease that is associated with CIPO.

In ACPO, patients are typically already hospitalized with a severe illness or after surgery.[13] The findings of abdominal distension can occur rapidly or after several days. Patients presenting with fever, severe abdominal tenderness, or peritonitis may have progressed to bowel ischemia or perforation from the increased distension.

The key feature of intestinal pseudo-obstruction is abdominal distension. As the differential for a distended abdomen is broad, imaging is useful in establishing a diagnosis. X-rays of the abdomen will demonstrate air-fluid levels with dilated loops of bowel. The pathognomonic finding for ACPO is a dilated colon from the cecum to the splenic flexure or even the rectum. Findings of a dilated colon are nonspecific, and thus further investigation beyond x-ray is required to confirm the diagnosis.

Abdominal CT scans are much more specific than abdominal x-rays. CT will also demonstrate dilated loops of bowel, air-fluid levels, or specifically proximal colonic dilatation from the cecum to the splenic flexure or even the rectum. No mechanical obstruction must be identified, such as closed-loop obstructions, hernias, strictures, or masses. In the acute setting, contrast enemas and small bowel follow-throughs can be essential adjuncts to rule out these obstructions.

Although no specific labs will suggest intestinal pseudo-obstruction, a liver profile and lipase should be obtained to rule out other causes of abdominal pain. A complete blood count and serum lactate should also be obtained as leukocytosis, and elevated serum lactate can be increased in cases of bowel ischemia and perforation. In patients with chronic symptoms, vitamin B12, folate, TSH, and celiac serology should be ordered to assess for metabolic and autoimmune abnormalities. Additionally, serologic testing for herpes simplex virus, cytomegalovirus, and Epstein-Barr virus can assist in the diagnosis as viruses may cause inflammation of the enteric nervous system causing CIPO.  Finally, antineuronal antibodies (ANNA-1/anti-Hu) can also be analyzed to assess for paraneoplastic immune-mediated pseudo-obstruction.[12]

Patients with a dilated colon and rectum raise suspicion for toxic megacolon. Stool cultures and stool evaluation for Clostridioides difficile toxin should be obtained, especially in patients with diarrhea. As metabolic abnormalities, including hypokalemia, hypomagnesemia, and hypocalcemia, have been associated with intestinal pseudo-obstruction, a metabolic panel should be obtained so that these may be repleted.

Patients with chronic symptoms may undergo further testing to identify the cause of symptoms. An upper endoscopy and colonoscopy should be performed to identify and locate any pathology or areas of obstruction. If an endoscopy demonstrates no abnormalities, scintigraphy, which assesses the motility of the gastrointestinal tract, may be employed. With scintigraphy, patients ingest resin pellets and undergo a series of imaging to assess the transit time. If an abnormality is seen on scintigraphy, a manometry study of the esophagus, stomach, and small intestine can delineate an underlying diagnosis and differentiate between myopathic and neuropathic disorders based on the pattern and amplitude of contraction.

As many neurological disorders are known to cause gastrointestinal dysmotility, autonomic function testing can differentiate peripheral neuropathy from central lesions.[5] In patients with severe dysmotility and known diagnosis, a full-thickness biopsy can be used to identify abnormalities in the enteric nervous system.

Treatment of ACPO involves decompression of the dilated colon to prevent bowel ischemia and perforation. Initial management in a stable patient may be conservative with serial x-rays of the abdomen to evaluate colonic diameter.[14] During this time, underlying causes should be treated and corrected.  These causes include electrolyte abnormalities, infections, and medication side effects (e.g., anticholinergics and opiates). A nasogastric tube connected to intermittent suction can be placed to assist in decompression and prevent aspiration. A rectal tube to dependent drainage can also be placed to assist in decompression. If no improvement is seen after 48-72 hours, neostigmine may be administered.[14]

Neostigmine is an acetylcholinesterase inhibitor that exhibits a parasympathomimetic effect by increasing the amount of available acetylcholine and indirectly stimulating muscarinic and nicotinic receptors.  These receptors, which are located on the smooth muscle of bowel mucosa, cause muscle contraction. The initial dose is 2 mg, administered slowly over 5 minutes.[15] Due to the side effect of bradycardia from neostigmine, patients should be placed in a monitored bed with telemetry and with atropine available at the bedside. A reduced dose should be used in patients with a history of heart block.

If the pharmacologic approach is unsuccessful or contraindicated, colonoscopic decompression should be considered. The colonoscope is advanced to the dilated bowel, and the air is suctioned. A decompression tube can also be placed up to the transverse colon with the aid of a guidewire to prevent re-occurrence.[13]

Surgery remains the final option when the above measures have failed or if the patient's condition continues to worsen. Options include placing a cecostomy tube or performing a colectomy.[16] A cecostomy involves placing a tube in the cecum which can drain and decompress outside of the abdomen. Alternatively, the dilated portion of the bowel can be resected with primary anastomosis or an ostomy. Any patient who develops peritonitis or becomes hemodynamically unstable presumably from bowel ischemia or perforation requires surgical evaluation and resection of the compromised bowel.

For patients with chronic symptoms, prokinetic agents can help treat oral intake intolerance. Erythromycin is useful in treating acute exacerbations by stimulating motilin receptors in the bowel.[17] This is useful in the hospitalized setting but has not been shown to be effective for long-term treatment.[18] For patients that cannot tolerate erythromycin, metoclopramide has proven to be effective. However, like erythromycin, it has not been proven effective for long-term treatment. Prucalopride and cisapride are prokinetic agents currently being investigated to improve gastric emptying and symptomatic relief.[19][20]

Proper nutritional assessment is also imperative for patients with CIPO.  Patients with oral intake intolerance should employ strategies such as small, frequent meals, and high-calorie drinks. If these adjuncts are unsuccessful in achieving caloric goals, feeding tube access through a gastrostomy tube. A jejunostomy may be indicated if there is evidence of gastroparesis in conjunction with CIPO.  Finally, patients with severe symptoms may require parenteral nutrition.

Mechanical Obstructions

Mechanical obstructions will present as dilation of bowel proximal to the obstructed point. Mechanical obstructions include incarcerated hernia, stricture, volvulus, or mass. Typically a "transition point" will be observed where proximal bowel is dilated and distal bowel compressed. If contrast is administered either by mouth or by enema, a cut-off may be seen.

Toxic Megacolon

In addition to abdominal distension on physical exam and abdominal radiograph, patients with toxic megacolon typically exhibit systemic inflammatory response syndrome (SIRS) criteria including fever, tachycardia, tachypnea, and altered mental status. The patients also more commonly have abdominal pain and bloody diarrhea. Toxic megacolon is commonly seen with ulcerative colitis but may also be seen with other types of colitis, e.g., ischemic, infectious, pseudomembranous. Clinical deterioration requires surgical evaluation for total colectomy with end ileostomy. 

Fecal Impaction

A dilated rectum and colon is commonly seen with fecal impaction. Patients with these findings should have a digital rectal exam to rule out impacted stool. Additionally, fecal matter can be seen on radiograph and CT imaging. Once the impaction is resolved, patients typically have a resolution of their symptoms.

The mortality rate for adult patients with CIPO is approximately 10%. One-third of patients with CIPO will require parenteral nutrition with its associated complications, which are estimated between 45% to 80%.[21]

In children, mortality rates range from 10% to 40%, with parenteral nutrition dependence as high as 60% to 80%.[22]

In ACPO, the prognosis is predicated on the development of bowel ischemia or perforation, which occurs in 3% to 15% of cases. The mortality rate with ischemic bowel or perforation is 40% versus 15% without perforation.[23][24]

Failure to address the colonic distension for intestinal pseudo-obstruction can result in the major complications of bowel ischemia or perforation, which may require urgent surgical intervention. As discussed previously, if a mechanical obstruction is not ruled out, the administration of neostigmine in a patient with a bowel obstruction can result in a catastrophic perforation.

Intestinal pseudo-obstruction is a relatively uncommon condition with broad and vague symptoms. Patients with chronic symptoms of unexplained abdominal distension and nausea should seek consultation with a gastroenterologist. Lifestyle modifications, nutritional assessment, and endoscopic interventions may be employed to rule out common etiologies for symptoms before further workup of intestinal pseudo-obstruction is initiated.

For acute and severe episodes of abdominal distension and oral intake intolerance, patients should report to the emergency room. Surgical emergencies (i.e., appendicitis, bowel obstruction, incarcerated hernias) must be ruled out before initiating the management of intestinal pseudo-obstruction.

Intestinal pseudo-obstruction is a disorder with unclear etiology and non-specific signs and symptoms, including abdominal distension, nausea, and vomiting. As this condition typically arises in patients who are critically ill or have had previous surgery, there may be a need for gastroenterologist or surgeon to be on the case. If abdominal imaging is obtained, the case should be discussed with a radiologist if bowel diameter or obstruction is not assessed. If patients fail to progress with supportive care, neostigmine may be used. The administration of neostigmine requires continuous cardiac telemetry, which may require admission to an intensive care unit or cardiac care unit.

Nurses play an important role in actively monitoring the vitals, specifically assessing for bradycardia. In these scenarios, specific instructions need to be relayed for atropine administration. The pharmacist can ensure that proper dosage is provided as well as ensure that there are no drug-drug interactions.  If neostigmine is unsuccessful, endoscopic decompression can be attempted by a gastroenterologist, general surgeon, or colorectal surgeon. If endoscopic decompression is still unsuccessful, then surgery is indicated either for colectomy or cecostomy. In specific situations for high-risk surgeries or those unfit for surgery, interventional radiology may be consulted for a percutaneous cecostomy. 

The above practice guideline is consistent with the Clinical Practice Guideline from the American Society of Colon and Rectal Surgeons and the American Society for Gastrointestinal Endoscopy. [Level 2]