Respiratory alkalosis occurs when hyperventilation reduces the PCO2, increasing serum pH. The most common cause of respiratory alkalosis is hyperventilation syndrome (Table 21–16), but bacterial septicemia and cirrhosis are other common causes. In pregnancy, progesterone stimulates the respiratory center, producing an average PCO2 of 30 mm Hg and respiratory alkalosis. Symptoms of acute respiratory alkalosis are related to decreased cerebral blood flow induced by the disorder.
Table 21–16.Causes of respiratory alkalosis. ||Download (.pdf) Table 21–16. Causes of respiratory alkalosis.
Decreased inspired oxygen tension
Cerebrovascular accident (infarction, hemorrhage)
Pharmacologic and hormonal stimulation
Recovery from metabolic acidosis
Interstitial lung disease
Determination of appropriate metabolic compensation may reveal an associated metabolic disorder (see Mixed Acid-Base Disorders).
As in respiratory acidosis, the metabolic compensation is greater if the respiratory alkalosis is chronic (see Table 21–11). Although serum HCO3– is frequently less than 15 mEq/L in metabolic acidosis, such a low level in respiratory alkalosis is unusual and may represent a concomitant primary metabolic acidosis.