Clinical relevance of ventilation during cardiopulmonary bypass in the prevention of postoperative lung dysfunction

Abstract

The current clinical study is the continuity of previous experimental findings in which ventilation during cardiopulmonary bypass (CPB) prevented reperfusion injury of the pulmonary arterial tree as demonstrated by preservation of vasorelaxation to acetylcholine (ACh) in swine. The aim of this prospective randomized study is to determine: 1) if ventilation during CPB prevents the selective endothelium-mediated lung dysfunction in humans and, 2) the clinical relevance of ventilation during CPB. Forty patients scheduled for primary coronary artery bypass grafting (CABG) were randomized into two groups: Group 1: Usual care (defined as no ventilation during CPB) and Group 2: CPB with low tidal volume ventilation (3 ml.kg-1) without positive end expiratory pressure (PEEP). To evaluate endothelial function, ACh was injected into the pulmonary artery and the changes in pulmonary vascular resistance index (PVRI) were measured at: (1) induction of anesthesia prior to surgery, (2) immediately after weaning from CPB and (3) 1 hour after CPB. In addition, secondary endpoints, such as PaO2/FiO2 ratio, mean pulmonary artery pressure (MPAP), postoperative length of stay (LOS) and postoperative pulmonary complications were measured to evaluate the effect of ventilation during CPB. To assess pulmonary complications, a chest x-ray was taken on the first and third postoperative days. There were no statistically significant changes in PVRI, PaO2 /FiO2 ratio, MPAP, postoperative LOS and postoperative pulmonary complications when comparing the non-ventilated and the ventilated groups during CPB. The ventilated group appears to obtain a greater vasorelaxation to ACh, as shown by the more pronounced change in PVRI when compared to the non-ventilated group. However, the difference in PVRI between the two groups was not statistically significant after weaning (p= 0.32) and 1hr after CPB (p= 0.28). Contrary to our hypothesis and due to larger than expected variability in the data, the hemodynamic and clinical changes seen were not statistically significant.