Positive end-expiratory pressure following coronary artery bypass grafting

Pulmonary dysfunction commonly follows open heart surgery. To evaluate the effects of positive end-expiratory pressure (PEEP) upon the course and severity of impaired oxygen transfer and roentgenographic evidence of atelectasis after coronary artery bypass grafting (CABG), we randomly assigned 44 patients to positive pressure ventilation and 0, 5, or 10 cm H2O PEEP. Study groups did not differ with respect to preoperative P(A-a)O2 or time on cardiopulmonary bypass. We observed a significant reduction of P(A-a)O2 during positive pressure ventilation with 10 cm H2O PEEP and FIO2 = 0.6 (182 +/- 6 vs 135 +/- 7 mm Hg, p less than .005). Following extubation, P(A-a)O2 measurements of the three groups did not differ when compared 24, 48, 72, 96, or 120 hours after surgery. Roentgenographic atelectasis scores did not differ on the fifth postoperative day. Five days after CABG, P(A-a)O2 exceeded preoperative P(A-a)O2 (29 +/- 1 vs 18 +/- 1 mm Hg, p less than .001), although the roentgenographic distances from hemidiaphragm to lung apex were unchanged (21.2 +/- 0.9 vs 22.0 +/- 0.9 cm). We conclude that routine PEEP improves pulmonary oxygen transfer but, once discontinued, PEEP offers no sustained beneficial effect upon impaired oxygen transfer or roentgenographic evidence of atelectasis following CABG.