Ventilation during cardiopulmonary bypass for prevention of respiratory insufficiency A meta-analysis of randomized controlled trials

Background: Cardiopulmonary bypass (CPB) is necessary for most cardiac surgery, which may lead to postoperative lung injury. The objective of this paper is to systematically evaluate whether ventilation during CPB would benefit patients undergoing cardiac surgery. Methods: We searched randomized controlled trials (RCTs) through PubMed, Embase, and Cochrane Library from inception to October 2016. Eligible studies compared clinical outcomes of ventilation versus nonventilation during CPB in patients undergoing cardiac surgery. The primary outcome includes oxygenation index (PaO2/FiO(2) ratio) or alveolar to arterial oxygen tension difference (AaDO(2)) immediately after weaning from bypass. The secondary outcomes include postoperative pulmonary complications (PPCs), shunt fraction (Q(s)/Q(t)), hospital stay, and AaDO(2) 4hours after CPB. Results: Seventeen trials with 1162 patients were included in this meta-analysis. Ventilation during CPB significantly increased post-CPB PaO2/FiO(2) ratio (mean difference [MD]=21.84; 95% confidence interval [CI]=1.30 to 42.37; P=0.04; I-2=75%) and reduced post-CPB AaDO(2) (MD=-50.17; 95% CI=-71.36 to -28.99; P<0.00001; I-2=74%). Qs/Qt immediately after weaning from CPB showed a significant difference between groups (MD=-3.24; 95% CI=-4.48 to -2.01; P<0.00001; I-2=0%). Incidence of PPCs (odds ratio [OR]=0.79; 95% CI=0.42 to 1.48; P=0.46; I-2=37%) and hospital stay (MD=0.09; 95% CI=-23 to 0.41; P=0.58; I-2=37%) did not differ significantly between groups. Conclusion: Ventilation during CPB might improve post-CPB oxygenation and gas exchange in patients who underwent cardiac surgery. However, there is no sufficient evidence to show that ventilation during CPB could influence long-term prognosis of these patients. The beneficial effects of ventilation during CPB are requisite to be evaluated in powerful and well-designed RCTs.