Table 4:

Mechanisms of hypercapnia

Mechanism of hypercapnia	Category	Pathophysiology	Examples
Hypoventilation	“Won’t breathe”	Decreased central respiratory drive	Sedatives (alcohol, benzodiazepines, opiates) Central disorders (encephalitis, stroke, medullary tumors, obesity hypoventilation)
Hypoventilation	“Can’t breathe”	Impaired function of respiratory muscles due to altered neuromuscular function	Myasthenia gravis, ALS, GBS, spinal cord injury Toxins: botulism, organophosphates Thyroid disorders
Hypoventilation	“Can’t breathe”	Chest wall disorders and pleural disease	Kyphoscoliosis, large pleural effusions, diaphragmatic paralysis, prior sternotomy/chest wall surgery, obesity
Increased proportion of dead space	“Can’t breathe”	Airway obstruction resulting in elevated V/Q ratios	Emphysema, hyperinflation, severe asthma, central airway obstruction
Increased proportion of dead space	“Can’t breathe”	Pulmonary vascular disease resulting in elevated V/Q ratios	Severe pulmonary embolism, pulmonary vascular disease, interstitial lung disease, ARDS
Increased CO2 production	“Can’t breathe enough”	CO2 production overwhelms pulmonary CO2 elimination	Fever, exercise, sepsis, hyperalimentation, thyrotoxicosis