The significance of diffusion hypoxemia

The phenomenon of "diffusion hypoxemia" seems to be a well-defined entity. To determine the degree of deoxygenation of the arterial blood due to diffusion hypoxemia, experiments were performed in monkeys which were anesthetized with ketamine, intubated, and allowed to breathe spontaneously. Blood PaO2 values were continuously monitored with the aid of an intra-arterially placed IBC PO2 electrode capable of instantly recording changes in oxygen tension. After stabilization of the blood PaO2 values with the animal breathing different mixtures of oxygen and nitrous oxide, the inspired mixture was abruptly changed to normal air. The blood PaO2 values did not show any significant fall in PaO2 with any mixture containing more than 21% oxygen. It is suggested that diffusion hypoxemia of any degree can be seen only if a patient is breathing a gas mixture containing no more than 21% oxygen.