What are the causes of metabolic alkalosis?

From the Guidelines

Metabolic alkalosis is primarily caused by excessive loss of hydrogen ions or gain of bicarbonate in the body, with the main causes including vomiting, diuretic use, excessive alkali administration, severe potassium depletion, and certain endocrine disorders. The underlying mechanisms often involve the removal of acidic gastric contents, increased bicarbonate reabsorption, or the administration of alkali-containing substances. According to 1, conditions like Bartter syndrome can also lead to hypokalemic metabolic alkalosis, highlighting the importance of considering inherited hypokalemia and salt-losing tubulopathy in the diagnosis.

Key Causes

• Vomiting or nasogastric suction, which removes acidic gastric contents
• Diuretic use, particularly loop and thiazide diuretics, which increase bicarbonate reabsorption
• Excessive alkali administration, such as sodium bicarbonate or antacids containing calcium carbonate
• Severe potassium depletion, as noted in 1, where hypokalemia is defined as K<3.5 mEq/L and can result from diuresis, potassium-free intravenous fluids, or other endocrine and renal mechanisms
• Certain endocrine disorders like hyperaldosteronism and Cushing's syndrome
• Contraction alkalosis due to dehydration, where the concentration of bicarbonate increases as fluid volume decreases
• Milk-alkali syndrome from excessive calcium and absorbable alkali intake

Addressing the Underlying Cause

For treatment to be effective, the underlying cause of metabolic alkalosis must be addressed, which typically involves fluid replacement with normal saline to correct volume depletion, potassium supplementation if hypokalemia is present, and discontinuation of offending medications. In severe cases, dilute hydrochloric acid may be administered intravenously under careful monitoring, as metabolic alkalosis can persist due to the kidneys continuing to reabsorb bicarbonate because of volume depletion, hypokalemia, or mineralocorticoid excess.

From the Research

Causes of Metabolic Alkalosis

The causes of metabolic alkalosis can be divided into several categories, including:

• Gain of bicarbonate or loss of nonvolatile acid from extracellular fluid 2, 3
• Loss of acid via the gastrointestinal tract or the kidney 2, 3, 4
• Excess base gained by oral or parenteral HCO3(-) administration or by lactate, acetate, or citrate administration 2, 3
• Factors that help maintain metabolic alkalosis, including:
  • Decreased glomerular filtration rate 2, 3, 4
  • Volume contraction 2, 3, 4
  • Hypokalemia 2, 3, 4
  • Hypochloremia 2, 3, 4
  • Aldosterone excess 2, 3, 4
• Clinical states associated with metabolic alkalosis, including:
  • Vomiting 2, 3, 4, 5
  • Mineralocorticoid excess 2, 3, 4
  • The adrenogenital syndrome 2, 3
  • Licorice ingestion 2, 3
  • Diuretic administration 2, 3, 4
  • Bartter's and Gitelman's syndromes 2, 3

Specific Causes

Some specific causes of metabolic alkalosis include:

• Profound vomiting or massive gastric drainage combined with concurrent oliguric renal failure 6
• Use of loop diuretics 4
• Primary aldosteronism 5
• Exogenous base gain 4