Pharmacologic Management of Constipation in the Critically Ill Patient

Asad E. Patanwala, Pharm.D.; Jacob Abarca, Pharm.D., M.S.; Yvonne Huckleberry, Pharm.D.; Brian L. Erstad, Pharm.D., FCCP


Pharmacotherapy. 2006;26(7):896-902. 

In This Article


The key finding of this study was that stimulant and/or osmotic laxatives were effective in producing a bowel movement in critically ill patients. In addition, opioid use and disease severity as defined by the APACHE II score were significant risk factors for constipation in this patient population. Note that 50% of the 50 patients in our study were defined as constipated. The effect of vasopressors seen in this analysis was contrary to what one might expect. Laxative use was more common among patients receiving vasopressors, which likely accounts for this finding.

The ideal pharmacologic regimen for the prophylaxis and treatment of constipation has yet to be determined for critically ill patients. Several classes of laxatives can be used; however, each has disadvantages. Saline laxatives (also referred to as osmotics) include magnesium hydroxide, magnesium citrate, and sodium phosphate. In patients with renal insufficiency or cardiac dysfunction, saline laxatives may cause electrolyte disturbances and volume overload from absorption of sodium, magnesium, or phosphorus.[5] Other osmotic laxatives include the poorly absorbed sugars such as lactulose, sorbitol, and polyethylene glycol.

Dehydration has been suggested as a cause of constipation in critically ill patients. Since osmotic laxatives work by drawing fluid into the gastrointestinal tract and possibly decreasing intravascular volume, this can compromise hemodynamic status in patients who already have intravascular fluid depletion.[3,6] However, the clinical significance of this is debatable, and we know of no published studies that have documented detrimental effects associated with the use of osmotics in critically ill patients.

Treatment of constipation with docusate for patients with chronic and terminal illness is based on inadequate experimental evidence.[7] Since gastrointestinal motility is decreased in these patients, softening of the stool may not prevent constipation.[8] Stool softeners are unlikely to be effective in the critically ill patient and, as evidenced by our study, have little utility when given alone for opioid-induced constipation. In addition, stool softeners are largely ineffective when administered without appropriate amounts of ingested fluids, which is often difficult to accomplish in the critically ill.

Bulk laxatives such as psyllium, methylcellulose, and polycarbophil may not be a reasonable choice for critically ill patients who need immediate relief from constipation. Moreover, these laxatives must be administered with adequate amounts of fluid, which may not be possible in these patients. Caution should be taken to avoid using bulk laxatives in patients who require fluid restriction, are confined to bed, or have strictures or partial obstructions.[9] The use of fiber-based laxatives may result in fecal impaction without adequate fluid intake and may further complicate existing fecal impaction.[8]

Common prokinetic agents in the United States include erythromycin and metoclopramide, although both of these agents have limitations with respect to efficacy and adverse effects. Critically ill patients are at increased risk for gastroparesis, and erythromycin has been suggested as the prokinetic agent of choice to increase gut motility in this patient population.[10] However, the beneficial effects of erythromycin on the stomach and small intestine that are mediated through motilin receptors do not extend to the colon. Furthermore, most studies involving erythromycin as a prokinetic agent have focused on enhancing gastric emptying and feeding tube migration.

In our study, metoclopramide was the most common prokinetic agent (25 patients); erythromycin was administered in only two patients. Prokinetic agent use was not associated with occurrence of a bowel movement. Although some critically ill patients receive these agents in combination with other laxatives to facilitate bowel function, we observed that metoclopramide was primarily used for postpyloric tube insertion and to decrease gastric residuals.

Two commonly used stimulant laxatives in the United States are senna and bisacodyl,[8] which work by increasing intestinal motility and secretions. Onset of action is within hours, and the major adverse effect is abdominal cramps.[5] Although stimulant laxatives have caused cathartic colon, no convincing evidence indicates that their long-term use causes structural or functional impairment of enteric nerves or intestinal smooth muscle.[11] They are unlikely to be harmful to the colon when administered at routine dosages.[12] However, melanosis coli, a brown-black pigmentation of the colonic mucosa, can develop in patients who take stimulant laxatives containing anthraquinones on a long-term basis. Most patients admitted to the MICU do not stay longer than a few weeks. In such circumstances, development of melanosis coli is highly unlikely. In our study, the use of senna was significantly associated with occurrence of a bowel movement and, although the use of bisacodyl was not significantly associated with bowel movement, a trend toward statistical significance was seen. When the results of both stimulant laxatives were combined, their efficacy was statistically significant.

Opioids alter neural input, inhibit peristaltic contractions and propulsion, and increase fluid absorption, leading to symptoms of bowel dysfunction. Activation of opioid receptors, particularly B5-receptors within the gastrointestinal tract, contributes to the pathophysiology of ileus after opioid use.[13] In our study, opioid use was negatively associated with a bowel movement in critically ill patients after controlling for other variables in the logistic regression analysis. Routine use of stimulant laxatives as a preventive measure is recommended for patients receiving long-term opioid therapy for pain control.[14] Some authors have recommended that these agents be given on a scheduled basis, and that patients continue taking them unless diarrhea occurs.[8] We believe this is an effective treatment strategy for critically ill patients since opioid-induced bowel dysfunction is common.

Debate continues regarding whether the term constipation can correctly be applied to the critically ill patient population. As mentioned earlier, constipation is a combination of various components, many of which cannot be assessed accurately in an unconscious or sedated patient. Using the same expectations for bowel motility in critically ill patients as in the general population does not seem appropriate. The term ileus usually denotes a more serious medical condition, and critically ill patients who simply have decreased bowel frequency are not necessarily considered to have an ileus. We believe that one bowel movement every 3 days is a reasonable expectation for critically ill patients after the first day of stabilization. Our definition of constipation (no bowel movement within the first 4 days of admission) is more conservative than the definition from a previous study (no bowel movement for 3 consecutive days).[3] In contrast to the previous study,[3] we followed patients only during the first 96 hours of admission.

In follow-up clinic visits in one study, patients stated they had experienced constipation in the intensive care unit.[6] Health professionals are obligated to anticipate constipation as a problem in this setting since it can contribute to patient morbidity. A multidisciplinary team approach is required for prevention of constipation. Although nurses are in an ideal position to assess, implement, and evaluate care for patients with constipation,[15] pharmacist-based interventions have contributed to increased laxative use in patients receiving opioids.[16]


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