Respiratory alkalosis, or primary hypocapnia, occurs when alveolar ventilation exceeds that required to eliminate the carbon dioxide produced by tissues. Concurrent decreases in Paco2, increases in pH, and compensatory decreases in blood HCO3- levels are associated with respiratory alkalosis. Respiratory alkalosis can be acute or chronic, with metabolic compensation initially consisting of cellular uptake of HCO3- and buffering by intracellular phosphates and proteins. Chronic respiratory alkalosis results in longer-lasting decreases in renal reabsorption of HCO3-; the arterial pH can approach near-normal values.