The Bottom Line: When diarrhea is the cause of metabolic alkalosis, rather than acidosis, the mechanism is determined by measuring the electrolyte content in stool. Large losses of chloride may occur in patients who have villous adenomas or other secretory diarrheas that cause depletion of chloride.
References: Seifter, J. (2014). Integration of acid-base and electrolyte disorders. The New England Journal of Medicine., 371(19), 1821-1831.
Summary: In this case, the electrolyte concentrations in liquid stool, if measured, would probably show a charge gap, in which (Na++K+)−Cl− would be less than the normal plasma bicarbonate concentration. High losses of chloride in stool, like losses of chloride from vomiting or after the use of loop diuretics, cause hypochloremic alkalosis
Table 2. Acid–Base Disorders and Their Causes According to the Relationship between Gains and Losses of Circulating Cations or Anions.