The effect of positive end-expiratory pressure on regional ventilation and perfusion in the normal and injured primate lung.

Although positive end-expiratory pressure (PEEP) is being employed in the management of respiratory insufficiency, many of its physiological effects remain undetermined. The cardiopulmonary effects of PEEP as well as its effect on regional ventilation and perfusion were studied in 10 baboons before and after pulmonary injury with oleic acid. In the normal lung, there was significant improvement in oxygenation at a PEEP of 5 cm. of water secondary to improved ventilation and perfusion in all PEEP greater than 5 cm. of water produced increasing mismatch of ventilation and perfusion in all zones. After oleic acid was injected, hypoxemia was evident with a reversal of the normal ventilation-perfusion (V/Q) relationship between upper and lower lung zones. This mismatch of ventilation and perfusion was corrected at a PEEP of 15 cm. of water. It was reasonable to conclude that the use of PEEP in the injured lung exerts it beneficial effect by balancing regional ventilation and perfusion in addition to increasing functional residual capacity.