The effects of PEEP on arterial oxygenation. An examination of some possible mechanisms.

The effect of positive and expiratory pressure (PEEP) on arterial oxygenation depends on many factors. Two of the most important are the "quality" and the "quantity" of the physiological shunt. The "quality" depends on the mixed venous oxygen tension, and the "quantity" on the shunt fraction. Each of these factors may rise or fall with PEEP, depending on the pulmonary and circulatory state of the patient. Their ultimate balance influences the change in arterial oxygen tension.