Respiratory failure occurs when the respiratory system fails in oxygenation and/or carbon
) elimination. The two types are:
- Hypoxaemic (type I)
- Hypercapnic (type II)
is less than 60 mm/Hg (8 kPa), with a normal or
, caused by ventilation-perfusion mismatch, with either/both:
- Under-ventilated alveoli (pulmonary oedema, pneumonia, or acute asthma).
- Venous blood bypasses ventilated alveoli (right to left cardiac shunts).
Hyperventilation increases CO2
removal, but does not increase oxygenation,
because the blood leaving unaffected alveoli is almost fully saturated.
is more than 50 mm/Hg (6.5 kPa), which
suggests inadequate alveolar ventilation. Any ventilation-perfusion mismatch will affect
, so arterial blood may be low, or normal.