Respiratory failure

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Respiration is sufficient when it is able to provide enough oxygen to and remove enough carbon dioxide from the tissues. If this is not the case, there is respiratory failure. There are two types of respiratory failure, partial and global.

Partial respiratory failure, also called hypoxaemic respiratory failure or type I respiratory failure, is characterised by hypoxaemia (decreased pO2) but no hypercapnia (elevated pCO2).

Complete respiratory failure, also called hypercapnic respiratory failure or type II respiratory failure, is characterised by both hypoxaemia and hypercapnia. This is more severe and also causes respiratory acidosis.

Etiology

Hypoxaemic respiratory failure

Hypoxaemic respiratory failure occurs due to problems with gas exchange in the lungs or due to mild V/Q mismatching. This is because CO2 exchanges much more easily in the lungs than O2.

Hypercapnic respiratory failure

Hypercapnic respiratory failure may occur due to (alveolar) hypoventilation or due to severe lung disease or increased dead space.

Hypoventilation

Physiological ventilation requires a normal respiratory drive from the CNS, normal conduction of nerve impulses from the CNS to the respiratory muscles, normal function of the chest wall and respiratory muscles, normal conduction of air through the upper airways, and normal functioning of the lungs.

As such, hypoventilation may occur due to problems in several different organ systems. Problems with the central nervous system can impair the normal drive to ventilate, problems with the peripheral nervous system, respiratory muscles, chest wall, or upper airways may make the patient unable to breathe despite the respiratory drive, and problems with the lung can impair gas exchange to such a degree that any amount of ventilation is insufficient for gas exchange.


Severe lung disease