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 CV collapse

Differential Diagnosis

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

Diagnosis

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

Treatment

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

See Also

Hypoxemia