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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

Table 21–17.Causes of respiratory alkalosis.

Clinical Findings

  • Acute respiratory alkalosis

    • Light-headedness

    • Anxiety

    • Paresthesias

    • Numbness about the mouth

    • Tetany in severe alkalosis from low ionized calcium


  • 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


  • 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

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