15. Constipation

Definition

There is no single definition for constipation.  It can be described as hard stools, infrequent stools (<3/week), need for excessive strain while stooling or the feeling of incomplete evacuation.

Etiology and Risk Factors

  • Small or Large bowel obstruction:
    • Volvulus, intra-abdominal adhesions, or masses
  • Ileus
  • Medication related:
    • Opioids
    • Calcium channel blockers
  • Metabolic disturbances: hypothyroidism, hypercalcemia
  • Pelvic floor muscle and anal sphincter dysfunction
  • Fecal impaction
  • Irritable bowel syndrome
  • Slow transit constipation: common in young women, delayed emptying of the proximal colon often.
  • “Functional” constipation: have a normal colonic transit time.

Evaluation and Differential Diagnosis

  • Evaluate for potential medication related causes (opioids, anticholinergics, iron)
  • Is the patient on a bowel regimen if they are on chronic opioids?
  • Does the patient pass flatus?
  • When was the last bowel movement?
  • Consider a rectal exam and abdominal x-ray to evaluate for obstruction if there is a suggestion of bowel obstruction or the patient has had prolonged constipation or new abdominal pain.

Management

  • Bulk Laxatives: psyllium, methylcellulose
  • Osmotic laxatives: sodium phosphate, magnesium citrate, magnesium hydroxide
  • Poorly absorbed sugars: lactulose, sorbitol, polyethylene glycol and electrolytes (Go-lytely), polyethylene glycol 3350 (Miralax).
  • Stimulant laxatives: senna, castor oil, mineral oil and bisacodyl.
    • Docusate, though popular, is ineffective.
  • Enema/suppository: Phosphate enema (Fleet), tap-water (500cc/day), lactulose retention enema, bisacodyl suppository.
    • Avoid fleet enemas in patients with CKD.
  • Manual disimpaction is often required to help remove stool from the bowel.

Key points

  • “Afterload before preload”: suppository/enema before stimulant.
  • All patients on chronic opioids should be on a bowel regimen including stool softeners and stimulant laxatives.
  • A reasonable starting regimen to treat uncomplicated constipation is senna and miralax; if not effective, add bisacodyl suppository, an enema, and/or manual disimpaction.
  • Exercise caution before adding powerful oral laxatives such as lactulose or Mg citrate for a patient with refractory constipation. First examine the patient; if the abdomen is firm or distended, obtain a KUB to rule out bowel obstruction.
  • Methyl-naltrexone can be helpful for refractory opioid induced constipation.

Lembo, A; Camilleri, M. “Chronic Constipation.” New England Journal of Medicine.349:14, 1360-68.

Pandolfino JE, Howden CW, Kahrilas PJ.  Motility-modifying agents and management of disorders of gastrointestinal motility. Gastroenterology 2000;118(2 Suppl 1):S32-47.