Hypercapnia

Background

• PaCO2 >45
• Exclusively caused by alveolar hypoventilation
  • Results from decrease in respiratory rate, tidal volume, or increase in dead space

Clinical Features

• Headache, confusion, lethargy, seizure, coma
• Extreme hypercapnia (acute elevation >100) can result in cardiovascular collapse

Differential Diagnosis

• Depressed central respiratory drive
  • Structural CNS disease: brainstem lesions
  • Drug depression of respiratory center: opioids, sedatives, anesthetics
  • Endogenous toxins: tetanus
• Thoracic cage disorders
  • Kyphoscoliosis
  • Morbid obesity
• Neuromuscular impairment
  • Neuromuscular disease: myasthenia gravis, Guillain-Barre
  • Neuromuscular toxin: organophosphate toxicity, botulism
• Intrinsic lung disease associated with increased dead space
  • COPD
• Upper airway obstruction

Evaluation

• ABG
  • HCO3 increases 1 mEq/L for each 10mmHg increase in PaCO2 (acute)
  • HCO3 increases 3.5 mEq/L for each 10mmHg increase in PaCO2 (chronic)

Management

• Increase minute ventilation (rate and/or tidal volume)

See Also

• Hypoxemia
• Shortness of breath
• Respiratory acidosis