Hypercapnia

Background

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

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

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

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)

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