alkalosis

Alkalosis is a condition in which body fluids have excess base or reduced hydrogen ion concentration, raising the blood pH above 7.45. It is generally classified as metabolic or respiratory, depending on whether the primary abnormality is bicarbonate elevation or carbon dioxide depletion. Compensation may occur but is not always complete.

Metabolic alkalosis results from loss of hydrogen ions or gain of bicarbonate. Common causes include prolonged vomiting or gastric suction, diuretic use, mineralocorticoid excess, and ingestion of bicarbonate or citrate (eg, antacids). Volume and potassium depletion often perpetuate it. A useful distinction is urinary chloride: chloride-responsive forms (urine Cl− < 20 mEq/L) occur with vomiting or diuretics, while chloride-resistant forms (urine Cl− > 20) relate to ongoing mineralocorticoid activity.

Respiratory alkalosis arises from excessive ventilation that lowers arterial carbon dioxide. Causes include anxiety, pain, fever, sepsis, pulmonary embolism, and high altitude. The reduced CO2 raises pH; renal compensation lowers bicarbonate over hours to days. Symptoms include lightheadedness, tingling, and, in severe cases, neuromuscular irritability.

Diagnosis relies on arterial or venous blood gas showing elevated pH with the characteristic secondary change (high HCO3− in metabolic, low PaCO2 in respiratory alkalosis). Additional tests include serum electrolytes and urinary chloride to guide management and distinguish chloride-responsive from chloride-resistant metabolic alkalosis.

Treatment targets the underlying cause and electrolyte disturbances. Metabolic alkalosis with volume depletion typically improves with isotonic saline and potassium repletion; in chloride depletion, restoring chloride aids correction. Severe cases may require agents such as acetazolamide to promote bicarbonate loss. Respiratory alkalosis is managed by addressing the precipitating cause of hyperventilation; severe cases may require ventilatory support.