Respiratory failure


Respiratory failure occurs when the respiratory system fails in oxygenation and/or carbon dioxide (CO2) elimination. The two types are:
Hypoxaemic: PaO2 is less than 60 mm/Hg (8 kPa), with a normal or low PaCO2, caused by ventilation-perfusion mismatch, with either/both: Hyperventilation increases CO2 removal, but does not increase oxygenation, because the blood leaving unaffected alveoli is almost fully saturated.

Hypercapnic: PaCO2 is more than 50 mm/Hg (6.5 kPa), which suggests inadequate alveolar ventilation. Any ventilation-perfusion mismatch will affect PaO2, so arterial blood may be low, or normal.

Causes of hypoxaemic respiratory failure

Causes of hypercapnic respiratory failure