Cardiopulmonary bypass decreases pulmonary vascular resistance index after coronary artery bypass surgery

Background. Decreased pulmonary vascular resistance index (PVRI) reflects favorable postoperative pulmonary circulation after coronary artery bypass grafting. This randomized study investigated whether cardiopulmonary bypass (CPB) impacts PVRI after coronary artery bypass grafting. Material and methods. A total of 47 patients undergoing coronary artery bypass grafting were randomized into four groups according to the ventilation and surgical technique: (1) No ventilation group, with intubation tube detached from the ventilator, (2) low tidal volume group, with continuous low tidal volume ventilation, (3) continuous 10 cm H2O positive airway pressure (CPAP) group, and (4) randomly selected patients undergoing surgery without CPB. Oxygenation index, pulmonary shunt, alveolar-arterial oxygen gradient and PVRI were determined. PVRI was calculated as the transpulmonary pressure gradient divided by cardiac index multiplied by 80. Results. During the first postoperative morning there were no statistical differences in oxygenation index, pulmonary shunt or alveolar-arterial oxygen gradient between the groups, while PVRI remained elevated in patients without CPB as compared with patients with CPB (263 +/- 98 vs. 122 +/- 84, dyne-s-cm(-5), respectively, p<0.001). PVRI decreased in all patients with CPB regardless of ventilation technique. In contrast, elevated postoperative PVRI values were predictive for patients without CPB (AUC 0.786; SE 0.043; p<0.001; 95% CI. 0.701-0.870). Conclusions. Modified ventilation does not affect PVRI in elective patients with healthy lungs during CPB. Instead, CPB per se may have an important role on diminished PVRI. We suggest that CPB preserves pulmonary arterial endothelial integrity.