Constipation

 

• Causes

  Bowel disease:

  • Anal fissure.
  • Anal stricture.
  • Rectal prolapse.
  • Colorectal carcinoma, though diarrhoea is commoner.
  • Crohn's stricture.
  • Bowel obstruction.
  • Compressive pelvic mass.

  Dietary:

  • Dehydration
  • Low fibre diet.

  Functional:

  • IBS, where it may alternate with diarrhoea.

  Metabolic:

  • Electrolytes: ↑Ca2+, ↓K+.
  • Hypothyroidism

  Neuropsychiatric:

  • Neurological e.g. spinal cord lesion, Parkinson's.
  • Depression, especially in older patients who tend to somatize more.

  Drugs:

  • Opiates
  • Iron
  • TCA
  • Diuretics
  • Calcium channel blockers.

• Investigations

  Basic approach:

  • PR exam.
  • Further investigations if: new-onset over 40 years old, or signs of colorectal carcinoma.

  Bloods:

  • FBC. Check ferritin and TIBC if microcytic anaemia found.
  • Check glucose for diabetic neuropathy.
  • Others: U+E, ESR, Ca2+, TFT, PSA.

  Imaging:

  • Abdo XR.
  • Lower GI endoscopy.

• Management

  • Increase fibre and fluid intake.
  • Encourage regular bowel movements.
  • Treat underlying cause.
  • If unsuccessful, try laxatives. Consider starting with macrogol or lactulose; add senna if unsuccessful.

• Laxatives

  Bulking agents

  • Types: ispaghula husk, methylcellulose, Sterculia
  • Mechanism: ↑faecal mass, easing intestinal transit.
  • Use: take with plenty of fluids. Onset is a few days.
  • Contraindications: dysphagia, obstruction, impaction.

  Stimulant laxatives

  • Senna, docusate (also a softener), glycerol, bisacodyl, sodium picosulfate (used pre-procedures).
  • Mechanism: alter water and electrolyte secretion and ↑GI motility.
  • Side effects: abdo cramps, GI irritation.
  • Contraindications: obstruction.

  Osmotic laxatives

  • Mechanism: poorly absorbed, osmotically-active substances, leading to fluid retention in the bowel.
  • Lactulose: especially useful in hepatic encephalopathy due to anti-ammonia effects. Side effects: bloating.
  • Macrogol (polyethylene glycol): especially useful in impaction (alternative: enema). Side effects: bloating, nausea.
  • Magnesium sulfate: rapid onset. Side effects: watery stool, urgency.

  Stool softeners

  • Docusate, arachis oil (enema), liquid paraffin.
  • Good for anal fissures.