Disruption of normal gastrointestinal function as a result of infection, hereditary or acquired diseases, or complications of surgical procedures uncovers its important role in acid-base homeostasis. Metabolic acidosis or alkalosis may occur, depending on the nature and volume of the unregulated losses that occur. Investigation into the specific pathophysiology of gastrointestinal disorders has provided important new insights into the normal physiology of ion transport along the gut and has also provided new avenues for treatment. This review provides a brief overview of normal ion transport along the gut and then discusses the pathophysiology and treatment of the metabolic acid-base disorders that occur when normal gut function is disrupted.
The gastrointestinal tract is a slumbering giant with regard to acid-base homeostasis. Large amounts of H+ and HCO3− traverse the specialized epithelia of the various components of the gut every day, but under normal conditions, only a small amount of alkali (approximately 30 to 40 mmol) is lost in the stool (1,2). In contrast to the kidney, acid and alkali transport in the gut is adjusted for efficient absorption of dietary constituents rather than for acid-base homeostasis. The small amount of alkali lost as a byproduct of these transport events is easily regenerated by renal net acid excretion, which is regulated by the kidney to maintain body alkali stores. Disruption of normal gut function, however, uncovers its power to overwhelm acid-base homeostasis. Acid-base disorders can vary from severe acidosis to severe alkalosis, depending on the site along the gastrointestinal tract affected and the nature of the losses that ensue. These disruptions in acid-base equilibrium are associated with disorders of potassium balance, often leading to either hypo- or hyperkalemia. Major sodium and chloride losses also occur, sometimes causing life-threatening volume depletion and almost always contributing to the acid-base abnormalities.