Changes in thoracopulmonary compliance and hemodynamic effects of positive end-expiratory pressure in patients with or without heart failure.

摘要

PURPOSE: The purpose of this study was to confirm that positive end-expiratory pressure (PEEP) has a different effect on cardiac index (CI) in patients with or without heart failure, even after controlling for differences in thoracopulmonary compliance (Ctp) and minimizing the secondary effects of PEEP related changes in oxygenation and breathing effort. MATERIALS AND METHODS: The hemodynamic effects of PEEP were evaluated in two groups of sedated and paralyzed patients with a low Ctp at 0 PEEP: 12 patients with normal pulmonary artery occlusion pressure (Ppao) and a CI > 2.5 L/min and 12 patients with a CI < 2.5 L/min and increased oxygen extraction ratio, despite a Ppao > 15 mm Hg. RESULTS: In patients with low CI and high Ppao, PEEP had no hemodynamic effect and Ctp remained low at all PEEP levels. However, PEEP-induced CI reduction in patients with normal cardiovascular function was associated with an increase in Ctp with incremental PEEP. Concerning PEEP-related hemodynamic effects, the significance between group differences persisted when data were analyzed after controlling for Ctp changes. However, Ctp changes with PEEP were the most significant correlators and discriminators of the magnitude and direction of PEEP-induced CI change. CONCLUSIONS: We conclude that (1) the observed different effect of PEEP on CI in patients with and without heart failure persists after the elimination of secondary effects due to underlying differences in Ctp, oxygenation, and breathing effort; and (2) PEEP-related changes in Ctp should be taken into consideration when dealing with the cardiovascular effects of PEEP. Our data support the hypothesis that, in addition to the transmission of PEEP to the pleural space, changes in lung volume are a significant determinant of PEEP-induced CI changes.