Why is the patient still hypoxic despite being ventilated?

The passage of oxygen from the atmosphere to the mitochondria is a complex process. Pathological conditions may affect this transfer at any step. The patient on the intensive care unit is particularly likely to be affected by disease or iatrogenic intervention. Hypoxia may be caused by an abnormal supply of oxygen, abnormalities of gas exchange, deficient transport in the blood or alterations in localized tissue utilization. An understanding of the principles involved will enable effective interpretation and subsequent management of the hypoxic patient.