Malabsorption
Definition
Malabsorption often comes with diarrhea, the book titles this chapter ‘Approach to the patient with diarrhea and malabsorption’, so here we’ll address the two in tandem. Normal stool frequency is anywhere from 3x per week to 3x per day, with a normal consistency defined by weight (200g or less). Greater frequency and/or weight suggests diarrhea. The acute form of diarrhea lasts less than 2 weeks, persistent diarrhea 2-4 weeks. Chronic diarrhea persists more than 4 weeks.
Diarrhea is a leading cause of mortality worldwide, particularly for children under 5 (in whom it is the second leading cause of death) or the elderly.
Pathophysiology
When food and drink is taken in it can be hypotonic (less osmotic pressure than plasma) or hypertonic (more osmotic pressure than plasma). Gastric, pancreatic, biliary and duodenal secretions are then added at the correct amount to make the meal approximately isotonic with the electrolytes of plasma by the time it gets to the duodenum. Ions (chloride and sodium) are then added and taken away, changing osmolarity as it goes. The intestines are usually net absorbers, regulated by sympathetic (adrenergic) and parasympathetic (cholinergic) activity and hormones.
Diarrhea is usually due to alterations of intestinal fluid and electrolyte transport, it may be due to increased small intestine secretion, or decreased colonic absorption (4L/day is maximum).
Based on the above, we categorise diarrhea is follows:
- Osmotic (water pulled out of plasma due to unabsorbable elements)
- Secretory (chloride secretion or inhibited sodium reabsorption, causing water to move)
- Inflammatory (an inflammatory process causes enterocyte damage, reducing sodium absorption)
Diarrhea can also be acute or chronic. Acute cases (<2wks) are commonly gastroenteritis, while chronic diarrhea with alternating constipation suggests irritable bowel.
Bloody diarrhea is an important subcategory of diarrhea, possible etiologies are:
- Campylobacter
- Shigella
- Salmonella
- E.coli
- Amoebiasis
- Ulcerative colitis/crohn’s
- Colorectal cancer
- Colonic polyps
Meanwhile mucus in the stool suggests IBS, colorectal cancer and polyps, and obvious pus (termed frank pus) suggests IBD, diverticulitis or a fistula. Explosive diarrhea may be cholera, giardia, yersinia and rotavirus.
With diarrhea the most important treatment is to ensure hydration, oral is better than IV, but if impossible you can give 0.9% saline + 20 mmol K+/L. Codeine phosphate (30mg/8h) or loperamide (2mg after each loose stool, max 16mg/day). Avoid ABs unless infective diarrhea is causing systemic upset (see below).