Ogilvie Syndrome

Etiology

The development of acute colonic pseudo-obstruction is unpredictable, and there are no definite causes; however, many clinical conditions that place a patient at increased risk have been identified. Advanced age, comorbidities associated with electrolyte imbalance or polypharmacy, and poor underlying functional status or immobility are all strongly associated. Older adults who have been hospitalized, even for non-operative care, are at increased risk. In a frequently cited retrospective study of 400 patients with ACPO, non-operative trauma, severe infection, and admission for cardiovascular disease were each considered predisposing conditions in approximately 10% of cases. Although all surgical operations place a patient at some increased risk for ileus, major orthopedic and obstetric procedures are most associated with the development of ACPO.

There appears to be a relationship to cesarean operations for unclear reasons. It is important to remember that not all patients that develop ACPO are hospitalized. Elderly adults presenting to the emergency department or other acute care settings from long-term care facilities or nursing homes, those with an underlying progressive neurological disease, or with recent abdominal surgery are all at increased risk.

Epidemiology

The incidence of this disease is frequently cited as approximately 100 cases per 100,000 hospital admissions every year, although some underreporting is suspected. Prevalence appears to be slightly increased in males, but the reason for this is unknown. The average age at presentation is approximately 60 years. Almost all patients have multiple underlying co-morbidities, and those who are functionally dependent at baseline develop the disease with the highest frequency. Surgical patients are most likely to be diagnosed on postoperative days 3 to 5.

Pathophysiology

While multiple risk factors for the development of ACPO have been established, a specific underlying mechanism has yet to be identified. Almost all investigators agree that there is impairment of the colonic motor system, with dysfunction or imbalance of the autonomic nervous system being the most likely cause. It is suspected that there is reduced activity of stimulatory neurotransmitters, chiefly acetylcholine, relative to that of the inhibitory neurotransmitters, nitrous oxide, and vasoactive intestinal peptide. Independent dysfunction of the enteric nervous system, as well as the intrinsic enteric reflex arcs and pacemaker activity, also contribute but to what degree is unknown.  Interestingly in ACPO, pathologic distension of the colon usually ends at, or just proximal to, the splenic flexure, which is also where autonomic parasympathetic efferent innervation transitions from the Vagus nerve to the sacral, S2-S4, nerve roots.

As the cecum and ascending colon dilate and the luminal diameter increases, wall tension in the colonic mucosa increases proportionately. This increased wall tension leads to colonic ischemia, fluid, and bacterial translocation, and eventually colonic perforation. Both the duration and absolute diameter of colonic dilation influence the risk of bowel ischemia or perforation. Very few cases of perforation have been reported when the cecal diameter is less than 12 cm. However, there is evidence of a direct correlation between an increasing diameter of more than 12 cm and the risk of complications. Duration of ACPO appears to be the greatest factor for perforation or ischemia, with dilation lasting more than 5 or 6 days conferring the highest risk and having a direct impact on mortality.[6][7][8][9]

History and Physical

Patients with acute colonic pseudo-obstruction will present with gradually worsening abdominal distension and some degree of abdominal discomfort. Nausea and vomiting will usually be present to some degree. Although bowel obstruction is classically taught to be associated with constipation and obstipation, a significant number of patients with ACPO will continue to have some degree of bowel function, and diarrhea is possible due to the hypersecretion of water. It is important to remember that the majority of these patients will have severe underlying co-morbidities or concurrent exacerbations of chronic disease, which may make the history unreliable.

The examination will invariably show some degree of abdominal distention. The abdomen will be tympanic, and auscultation should reveal the presence of bowel sounds classically high-pitched. Some degree of abdominal tenderness is expected on the exam. Fever and any severe abdominal tenderness with or without signs of peritonitis are ominous findings suggestive of ischemia and perforation. Signs of peritonitis with abnormal vital signs should be concerning for sepsis.

Evaluation

Acute colonic pseudo-obstruction is an uncommon cause of bowel obstruction and is generally considered a diagnosis of exclusion. A thorough assessment, including contrast imaging, is necessary before the diagnosis of ACPO can be definitively made. Furthermore, the evaluation must assess for potentially reversible causes of ACPO and attempt to determine if any complications, such as ischemia or perforation, are present or imminent. 

Laboratory tests, although non-specific to the diagnosis, complete a thorough evaluation. If not associated with underlying disease, leukocytosis, elevated CRP, or lactate are concerning for bowel ischemia. Liver function tests, lipase, and human chorionic gonadotropin (HCG) should be obtained to help rule out other causes of acute abdominal pain. Electrolyte abnormalities, including magnesium and calcium, are common and have been reported present in up to two-thirds of post-operative patients. Thyroid function should be evaluated if a recent test is not available. Patients with diarrhea should be evaluated for Clostridium difficile toxin. Consider blood cultures in patients who appear septic.

Appropriate imaging is essential to the diagnosis and management of ACPO. Plain radiography, consisting of upright and supine abdominal films, is commonly performed but is limited in its utility. Expected findings include varying degrees of colonic dilatation, normal haustral markings, and lack of signs of mechanical obstruction such as volvulus. Free air on acute abdominal series increases concern for perforation but does not rule perforation out. Perhaps the most important use of plain radiography is to measure the degree of initial colonic dilatation and for serial imaging during observation after diagnosis is made. CT scan with oral and intravenous (IV) contrast is the preferred modality for diagnosis. Rectal contrast is helpful but has been associated with iatrogenic perforation. Gastrografin or other water-soluble enteral contrast should be used. CT will rule out anatomic or mechanical bowel obstruction as well as evaluate for more obscure causes of dilatation, such as retroperitoneal hematoma or abdominal abscess. CT scans can also show signs of ischemia, such as mucosal wall thickening, submucosal edema, or gas. Classically, ACPO on CT scan will show isolated dilatation of the cecum and ascending colon with a gradual transition zone or "cut off" at the splenic flexure. If a CT scan is not available, and peritonitis is not appreciated during the examination, a contrast enema study can be performed, which has a reported sensitivity of up to 96% in making a diagnosis of ACPO. Lastly, diagnostic colonoscopy should be avoided in all patients with suspected ACPO, as gas insufflation is associated with an increased risk of perforation.

Treatment / Management

The primary goal of treatment is urgent bowel decompression. Treatment options for ACPO include conservative therapy with observation, direct pharmacologic interventions, and endoscopic therapies. Surgical or open-operative interventions are reserved for those failing endoscopic procedures or for patients who develop ischemia or perforation. The recommendations discussed in this article are consistent with those of the American Society of Colon and Rectal Surgeons 2016 guidelines.

Patients diagnosed with uncomplicated ACPO should be admitted to the hospital to a unit where they can be carefully monitored. Initial management includes nothing by mouth (NPO) status and placement of a nasal gastric tube to aid in decompression. Patients should be carefully resuscitated with fluid as indicated. Electrolyte abnormalities should be aggressively corrected as well as any other underlying disease exacerbations. Medications that impact colonic motility, such as opiates and anticholinergics, should be discontinued as soon as possible, and it is also recommended that laxative medications be stopped. Patients should attempt to ambulate as frequently as clinically tolerated and, while in bed, should be encouraged to lie prone or in a knee-to-chest position with frequent turns to promote passage of flatus. Frequent repeat abdominal examinations are required. Laboratory tests, especially complete blood count (CBC) and electrolytes, are recommended to be collected at least daily. A daily abdominal plain film should be obtained to monitor cecal dilatation. If there is no development of signs of complicated disease and the cecal diameter remains less than 12 cm, this conservative approach should be continued for 72 hours and has a success rate of up to 90%.

Pharmacologic therapy should be initiated for patients who do not improve within 72 hours, have a duration of ACPO greater than 4 days, or develop a cecal diameter of greater than 12 cm. Neostigmine, a short-acting acetylcholinesterase inhibitor, is the drug of choice for treatment of ACPO, and evidence and popularity for its use in uncomplicated disease are quickly increasing. The resolution of disease is defined clinically as the passage of flatus or stool and or decreasing cecal diameter. The medication is usually administered as a 2-mg, slow IV push over 2 to 5 minutes. Contraindications and adverse effects should be reviewed before use. Common adverse effects include abdominal discomfort, salivation, and vomiting, which are usually benign and transient. Patients should be closely monitored for more severe complications such as bradycardia and bronchorrhea. It is recommended that patients be on a continuous cardiac monitor during administration and for 30 additional minutes after administration. Atropine for symptomatic bradycardia should be available per ACLS guidelines. Glycopyrrolate can be used for concerning respiratory secretions. A clinical response is typically seen within 2 to 30 minutes of administration. The average efficacy after one dose of neostigmine in randomized controlled trials is approximately 90%, with most non-responders having a resolution of disease after a second 2-mg dose, which can be given 90 minutes to 3 hours after the first. A 24-hour neostigmine drip regimen has also been evaluated with a reported success rate of 85% and with fewer reported adverse effects. After an initial response to neostigmine, patients should continue to be monitored as approximately 30% are at risk of recurrence of cecal dilatation. There is evidence that oral administration of polyethylene glycol immediately after neostigmine response prevents this.

Patients who have contraindications to or fail pharmacologic therapy should be evaluated for endoscopic decompression. The procedure is considered technically difficult, and success rates are directly related to operator experience. Decompression is attempted through colonoscopy without gas insufflation or bowel preparation. After the dilated bowel has been evaluated and suction has removed air, a colonic decompression tube is usually placed as close to the cecum as possible via the endoscope. The decompression tube is then left to drainage externally with intermittent flushes. There is an approximately 3% risk of iatrogenic perforation during this procedure, and reoccurrence is still possible, although the placement of a decompression tube significantly reduces this event.

Traditional operative management is necessary when the interventions above are unsuccessful or when there is the development of bowel ischemia or perforation. If a perforation is not present, a cecostomy decompression procedure can be attempted. If there is severe ischemia found on endoscopy or perforation occurs, some degree of open resection is indicated with likely Hartmann procedure. Mortality rates increase substantially in ACPO when operative management is needed, regardless of whether perforation or non-viable bowel is present, and all attempts should be made to manage this disease more conservatively.[10][11][12](B3)

Differential Diagnosis

The differential diagnosis of ACPO includes:

• Volvulus (cecal, sigmoid)
• Mesenteric ischemia
• Toxic megacolon
• Incarcerated hernia
• Intussusception
• Stricture
• Malignancy   
• Adynamic ileus 
• Constipation or stool impaction

Prognosis

The expected prognosis is confounded by the association of multiple co-morbidities in the usual patient population, as well as the underlying disease contributing to the development of ACPO. In general, the expected mortality after diagnosis of uncomplicated ACPO is approximately 15%. Complicated ACPO occurs in 3% to 15% of patients, which is associated with a much worse prognosis with average mortality rates between 30% and 40%. Factors associated with the development of complications include cecal diameter and duration of illness. In one study, no patients with a cecal diameter of less than 12 cm developed complicated disease, but 23% of patients with a cecal diameter of 14 cm did. Duration of dilation appears to have the most direct association with complicated disease and becomes concerning after 5 days, with a reported 5-fold increase in mortality rate after 7 days of unresolved disease. In patients who are actively treated, operative management has the highest mortality rate, which is likely due to operative therapy being reserved for those with complications or prolonged disease course; even without bowel ischemia, postoperative mortality rates are 26%. As can be seen, patient prognosis and survival depend on recognition, diagnosis, and timely colonic decompression.