Pulmonary Physiology, Oxygen Delivery & Uptake, Dr. D. Penney

Table 9.01. Classification of the causes of hypoxia in terms of alveolar PO2, arterial P02, arterial oxygen content, venous P02, and venous oxygen content. The last column indicates whether increased inspired fractional oxygen will alleviate the problem.

The panels in Figure 9.01 present the major features of the four classical hypoxias compared with the normal condition where arterial PO2 is 100 mmHg, arterial Hb saturation 98%, arterial O2 content 20 vols %, (mixed) venous PO2 40 mmHg, saturation about 75% (shown here closer to 65%), O2 content about 15 vols % and arterio-venous (a-v) content difference between 4 - 6 vols %.

Clearly, increased inspired oxygen is useful in treating most forms of hypoxic hypoxia, while it is not useful in treating stagnant and histotoxic hypoxia. Increased inspired oxygen is the indicated approach to carbon monoxide hypoxia (poisoning).

In severe cases (COHb greater than 25%), inspired P02 is raised to nearly 2000 mmHg for 30-60 minutes by placing the CO victim in a hyperbaric chamber. This forces more oxygen into solution in the blood, supply the oxygen-starved tissues and also drives CO off the Hb so it can once again carry oxygen.

Last Changed 04/28/00

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