Alkalosis, Respiratory

Key Features

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

• Occurs when hyperventilation reduces the PCO₂, increasing serum pH

• Causes (Table 21–16)

  • Hypoxia

    • Decreased inspired oxygen tension

    • Ventilation-perfusion inequality

    • Hypotension

    • Severe anemia

  • CNS-mediated disorders

    • Voluntary hyperventilation

    • Anxiety-hyperventilation syndrome

    • Cerebrovascular accident (infarction, hemorrhage)

    • Infection

    • Trauma

    • Tumor

  • Pulmonary disease

    • Interstitial lung disease

    • Pneumonia

    • Pulmonary embolism

    • Pulmonary edema

  • Mechanical overventilation

• In pregnancy progesterone stimulates the respiratory center, producing an average PCO₂ of 30 mm Hg

Clinical Findings

• Light-headedness

• Anxiety

• Paresthesias

• Perioral numbness

• Tetany in severe alkalosis from low ionized calcium

Diagnosis

• Arterial blood pH is elevated, and PCO₂ is low

• Serum bicarbonate is decreased in chronic respiratory alkalosis

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