Alkalosis is a pathologic process that results in a decrease in the overall hydrogen ion concentration in the body. A metabolic alkalosis is the result of an elevated serum bicarbonate concentration. The normal serum bicarbonate level is 23 to 28 mEq/L. Therefore, a metabolic alkalosis is a serum bicarbonate level >28 mEq/L. The most common causes of metabolic alkalosis in children are emesis and diuretic use. The etiologies of metabolic alkalosis are divided into two categories based on the urine chloride level. A metabolic alkalosis can be thought of as a failure of the kidney to eliminate bicarbonate at a normal capacity.

If the urine chloride is <15 mEq/L, the metabolic alkalosis is considered to be chloride-responsive. This type of metabolic alkalosis usually exists with a concurrent potassium deficiency to decrease the glomerular filtration rate or enhance proximal fractional bicarbonate reabsorption or both. This combination of disorders evokes secondary hyperreninemic hyperaldosteronism. The alkalosis may be improved by correcting the chloride deficit through the administration of a chloride salt, either sodium chloride or potassium chloride. Common causes of chloride responsive metabolic alkalosis include gastric losses due to emesis or nasogastric suction, loop or thiazide diuretics, chloride-losing diarrhea, chloride-deficient formula, cystic fibrosis, and posthypercapnic states.