Objective: To investigate the effect of positive and-expiratory pressure (PEEP) on the longitudinal distribution of pulmonary vascular resistance in patients immediately after coronary artery bypass grafting.
Design: Prospective, intervention study.
Setting: Postcardiac surgery intensive care unit in a teaching institution.
Patients: Twenty patients after elective coronary artery bypass grafting.
Intervention: The effect of PEEP on pulmonary circulation, at four different levels (0, 5, 10, and 15 cm H2O), was analyzed in 20 patients.
Measurements and main results: Mean pulmonary arterial pressure, left atrial pressure, pulmonary artery occlusion pressure, and pulmonary capillary pressure were measured at each PEEP level. A model consisting of two resistances in series was used to analyze the effect of PEEP on the pulmonary circulation. The pulmonary vascular resistance for each area (arterial and venous) of the circulation was calculated. Pulmonary vascular resistance increased from 216 +/- 70 dyne.sec/cm5 at a PEEP of 0 cm H2O to 308 +/- 125 dyne.sec/cm5 at a PEEP of 15 cm H2O (p < .001). This increase, however, resulted solely from an increase in the resistance of the venous part of the pulmonary circulation from 66 +/- 29 to 134 +/- 69 dyne.sec/cm5 (p < .001), without any change in pulmonary arterial resistance.
Conclusions: PEEP increases pulmonary vascular resistance solely by increasing pulmonary venous resistance. When applying PEEP, changes in pulmonary vascular resistance may impede the resorption of pulmonary edema fluid.