Function of each lung during mechanical ventilation with ZEEP and with PEEP in man anesthetized with thiopental meperidine

Abstract

Differential lung function was studied in 7 healthy adult volunteers who were anesthetized, paralyzed, and mechanically ventilated. After initial measurements during ventilation with positive end expiratory pressure (PEEP), studies were repeated during ventilation with zero (ambient) end expiratory pressure (ZEEP). The measurements were made with the subject in the supine and the two lateral decubitus positions during PEEP and in reversed order during ZEEP. Reduction in end expiratory pressure from approximately 9 cm H2O to ambient pressure resulted in significant decreases in total functional residual capacity (FRC) in both supine and lateral positions. Mean percentages of total ventilation, pulmonary capillary blood flow, and CO2 elimination of the nondependent lung increased significantly in the lateral position with decreases in end expiratory pressure. Mean percentage of FRC of the nondependent lung in the lateral position did not achieve a significant alteration with reduction of end expiratory pressure. The alterations in the intrapulmonary distribution of gas and blood flow observed with changes in end expiratory pressure are consistent with the concepts that the decrease in FRC that occurs after induction of anesthesia alters regional lung volumes, resulting in altered gas distribution, and variations in alveolar pressure (ZEEP versus PEEP) might cause larger changes in alveolar pressure than in pulmonary arterial pressure.