Positive end-expiratory pressure increases pulmonary venous vascular resistance in patients after coronary artery surgery

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Abstract
To investigate the effect of positive end-expiratory pressure (PEEP) on the longitudinal distribution of pulmonary vascular resistance in patients immediately after coronary artery bypass grafting. Prospective, intervention study. Postcardiac surgery intensive care unit in a teaching institution. Twenty patients after elective coronary artery bypass grafting. The effect of PEEP on pulmonary circulation, at four different levels (0, 5, 10, and 15 cm H2 O), was analyzed in 20 patients. 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[centered dot]sec/cm sup 5 at a PEEP of 0 cm H2 O to 308 +/- 125 dyne[centered dot]sec/cm5 at a PEEP of 15 cm H2 O (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[centered dot]sec/cm5 (p <.001), without any change in pulmonary arterial resistance. 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. (Crit Care Med 1997; 25:767-772)