Alkalosis, Respiratory

Key Features

• Occurs when hyperventilation reduces the PCO₂, increasing serum pH

• The most common cause is hyperventilation syndrome (Table 21–16)

• Bacterial septicemia and cirrhosis are other common causes

• Pregnancy is another cause of chronic respiratory alkalosis; progesterone stimulates the respiratory center, producing an average PCO₂ of 30 mm Hg

Clinical Findings

• Acute respiratory alkalosis

  • Light-headedness

  • Anxiety

  • Paresthesias

  • Perioral numbness

  • Tetany in severe alkalosis from low ionized calcium

Diagnosis

• Elevated arterial blood pH, low PCO₂

• Serum HCO₃^– is decreased in chronic respiratory alkalosis

• Although serum HCO₃^– is frequently < 15 mEq/L in metabolic acidosis, such a low level in respiratory alkalosis is unusual and may represent a concomitant primary metabolic acidosis

Treatment

• Treatment is directed toward the underlying cause

• Rapid correction of chronic respiratory alkalosis may result in metabolic acidosis as PCO₂ is increased in the setting of previous compensatory decrease in HCO₃^–

• In acute hyperventilation syndrome from anxiety,

  • Breathing into a paper bag should be discouraged because it does not correct PCO₂ and may decrease PO₂

  • Sedation may be necessary if the process persists

• The severity of hypocapnia in critically ill patients has been associated with adverse outcomes