Correct!
2. Neostigmine, an acetylcholinesterase inhibitor, may be effective in producing rapid colonic decompression
Neostigmine, an acetylcholinesterase inhibitor, may be effective in producing rapid colonic decompression. In a prospective, double-blind, placebo-controlled trial of neostigmine in acute colonic pseudo-obstruction of 21 patients, 11 patients received 2.0 mg of neostigmine intravenously and 10 patients received intravenous saline. Prompt decompression was observed in 11 patients (91 percent) who received neostigmine compared to none receiving placebo, with a time to respond ranging from 3 to 30 minutes and a median of 4 minutes. The most frequent adverse effect was mild to moderate transient crampy abdominal pain. Excessive salivation and vomiting were also noted in a few patients. Symptomatic bradycardia requiring atropine was observed in two patients. Bronchospasm and hypotension have been reported (1). Therefore, neostigmine should be used with caution in patients with bronchial asthma, recent myocardial infarction, and concurrent therapy with beta-blockers. In addition, atropine should be available at the bedside and patients should receive continuous electrocardiographic monitoring with vital sign for 30 minutes. The use of neostigmine in pregnancy has not been well-studied (6). The rate of recurrence of acute colonic pseudo-obstruction after neostigmine ranges from 5 to 33% (7).
Other pharmacologic agents include erythromycin and methylnaltrexone. Erythromycin binds to motilin receptors in the intestine and stimulates smooth muscle contraction. It can be administered intravenously (250 mg every eight hours for three days) or orally (250 mg by mouth four times a day for ten days) (8). Methylnaltrexone has been reported in a case report to be effective in patients with acute colonic pseudo-obstruction that occurs post-operatively, secondary to opioid use, or persists after two injections of neostigmine (9). However, large prospective studies are needed to determine the role of methylnaltrexone in the treatment of patients with acute colonic pseudo-obstruction associated with opioid use.
An algorithm for the approach to patients with acute colonic distention has been proposed (Figure 2) (10).
Figure 1. Algorithm for the approach to patients with acute colonic distention. (Reproduced with permission from: Eisen GM, Baron TH, Dominitz JA, et al. Acute colonic pseudo-obstruction. Gastrointest Endosc 2002; 56:789. Copyright © 2002 Elsevier).
In pseudo-obstruction, if conservative management has a partial/no response, neostigmine should be administered. If neostigmine fails, colonic decompression is recommended. Colonic decompression resolves 70% of acute colonic pseudo-obstruction as measured by reduction in cecal diameter radiographically (2). Surgical cecostomy/percutaneous cecostomy is the last resort if all measures fail to resolve acute colonic pseudo-obstruction because it is associated with high morbidity and mortality (11).
Case continued:
Despite the rectal tube, NPO and NG decompression, the patient continued to have abdominal distention. He developed progressive dyspnea and hypoxemia requiring more supplemental oxygen. On exam, he is tachypneic, tachycardic and hypertensive. His oxygen saturation is 92% on 6 liters nasal cannula. On auscultation of his chest, coarse breath sounds at the right bases greater than left base. His abdominal exam is unchanged. The rest of his exam is unremarkable. His laboratory studies are significant for hypernatremia (Na+ 150 mmol/L), hypokalemia (K+ 3.2 mmol/L) and thrombocytopenia (Platelets 81,000 /μL).
Which of the following laboratory abnormalities are seen in acute colonic pseudo-obstruction? (Click on the correct answer to proceed to the next panel)