Page 8 - Respiratory Failure

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Pathophysiology

The main path physiologic mechanisms of respiratory failure are:

• Hypoventilation: in which PaCO2 and PaO2 and alveolar-arterial PO2 gradient are normal.
Depression of CNS from drugs is an example of this condition.

• V/P mismatch: this is the most common cause of hypoxemia. Administration of 100% O2

eliminates hypoxemia.

• Shunt: in which there is persistent hypoxemia despite 100% O2 inhalation. In cases of a shunt, the

deoxygenated blood (mixed venous blood) bypasses the alveoli without being oxygenated and

mixes with oxygenated blood that has flowed through the ventilated alveoli, and this leads to

hypoxemia as in cases of pulmonary oedema (cardiogenic or noncardiogenic), pneumonia and

atelectasis