Diarrhea (and other losses of intestinal secretions) and ureteral diversion can lead to a variety of acid-base and electrolyte abnormalities. The types of changes that can occur, the etiology mechanisms, and issues related to diagnosis and treatment will be reviewed here.
DIARRHEA AND OTHER LOSSES OF INTESTINAL SECRETIONS
The intestinal secretions below the stomach, including pancreatic and biliary secretions, are relatively alkaline with a total base concentration of 50 to 70 meq/L . The following acid-base and electrolyte abnormalities can be seen:
- Metabolic acidosis due to the loss of alkaline fluid, although laxative abuse may also be associated with metabolic alkalosis.
- Hypokalemia, which can be induced by diarrhea, a villous adenoma, or the removal of pancreatic, biliary, or intestinal secretions (by tube drainage, fistulas, or vomiting with intestinal obstruction).
- Patients who become volume depleted may develop hypernatremia if the free water losses are not replaced, or hyponatremia due to an inability to excrete ingested water because of the hypovolemic stimulus to the release of antidiuretic hormone. (See "Etiology and evaluation of hypernatremia", section on 'The importance of thirst' and "Causes of hyponatremia".)
Laxative abuse — Occult laxative abuse (a form of factitious diarrhea) should be suspected in any patient with an unexplained normal anion gap metabolic acidosis and hypokalemia [2-4]. Other findings that may be present include volume depletion and moderate to severe hypermagnesemia if a magnesium-containing cathartic is used (in some cases, the magnesium is taken inadvertently with antacids or food supplements) [3,5]. (See "Factitious diarrhea".)
For reasons that are not well understood, many patients with laxative abuse present with metabolic alkalosis rather than the expected metabolic acidosis [1,3]. This situation typically occurs with laxatives that primarily act as stimulants of the colon. Since colonic fluid has a high potassium content, patients who abuse these drugs tend to develop significant total body potassium depletion.