Chapter 74: Constipation

INTRODUCTION AND EPIDEMIOLOGY

Constipation is an extraordinarily common cause of patient morbidity in the United States.^1,2,3,4 The incidence of constipation increases with age, with 30% to 40% of persons >65 years old citing constipation as a problem.^4,5 Constipation affects as many as 80% of critically ill patients and is directly associated with patient mortality in this population.⁶

Physicians and patients define constipation differently. Physicians have traditionally defined constipation as fewer than three bowel movements per week. In contrast, patients commonly define constipation in terms such as abdominal discomfort, bloating, straining during bowel movements, or the sensation of incomplete evacuation. Consequently, constipation should not be defined simply by stool frequency alone, because doing so maximizes the potential to underdiagnose a significant number of patients who suffer from the condition.⁷ The Rome criteria for the definition of constipation consist of two or more of the following signs or symptoms: (1) straining at defecation at least 25% of the time, (2) hard stools at least 25% of the time, (3) incomplete evacuation at least 25% of the time, (4) fewer than three bowel movements per week, (5) symptoms for at least 12 weeks (consecutive or nonconsecutive) in the preceding 12 months for chronic constipation.⁸

PATHOPHYSIOLOGY

Constipation is a complicated condition with multiple, often overlapping causes (Table 74-1). Gut motility is affected by diet, activity level, anatomic lesions, neurologic conditions, medications, toxins, hormone levels, rheumatologic conditions, microorganisms, and psychiatric conditions. Constipation is best thought of as either acute or chronic, as doing so helps formulate a differential diagnosis. Due to the rapidity of symptom onset, acute constipation is intestinal obstruction until proven otherwise. Common causes of intestinal obstruction include quickly growing tumors, strictures, hernias, adhesions, inflammatory conditions, and volvulus. Other causes of acute constipation include the addition of a new medicine (e.g., narcotic analgesic, antipsychotic, anticholinergic, antacid, antihistamine), change in exercise or diet (e.g., decreased level of exercise, fiber intake, or fluid intake), and painful rectal conditions (e.g., anal fissure, hemorrhoids, anorectal abscesses, proctitis). Chronic constipation can be caused by many of the same conditions that cause acute constipation. However, some specific causes of chronic constipation include neurologic conditions (e.g., neuropathies, Parkinson's disease, cerebral palsy, paraplegia), endocrine abnormalities (e.g., hypothyroidism, hyperparathyroidism, diabetes), electrolyte abnormalities (e.g., hypomagnesia, hypercalcemia, hypokalemia), rheumatologic conditions (e.g., amyloidosis, scleroderma), and toxicologic causes (e.g., iron, lead).