Alkalosis, Respiratory

For further information, see CMDT Part 21-22: Respiratory Alkalosis

Key Features

• Elevated arterial blood pH (> 7.45), low PCO₂ (< 32 mm Hg)

• Occurs when hyperventilation reduces the PCO₂, increasing serum pH

• The most common cause is hyperventilation syndrome (Table 21–17)

• Bacterial septicemia and cirrhosis are other common causes

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

Clinical Findings

• Acute respiratory alkalosis

  • Light-headedness

  • Anxiety

  • Paresthesias

  • Numbness about the mouth

  • Tetany in severe alkalosis from low ionized calcium

Diagnosis

• Elevated arterial blood pH (> 7.45), low PCO₂ (< 32 mm Hg)

• Serum HCO₃^– is decreased (< 22 mEq/L or < 22 mmol/L) in chronic respiratory alkalosis

• Although serum HCO₃^– is frequently below 15 mEq/L in metabolic acidosis, it is unusual to see such a low level in respiratory alkalosis, and its presence implies a superimposed (noncompensatory) metabolic acidosis

Treatment

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

• Treatment is directed toward the underlying cause

• In acute hyperventilation syndrome from anxiety, rebreathing into a paper bag increases PCO₂. Sedation may be necessary if the process persists