The protective effect of hypothermia on postoperative cognitive deficit may be attenuated by prolonged coronary artery bypass time: Meta-analysis and meta-regression

There is controversy about whether hypothermia during coronary artery bypass grafting (CABG) surgery is effective in reducing postoperative cognitive deficit (POCD). The objective of this study was to determine the effect of hypothermia on POCD and to undertake a meta-regression to determine whether moderator variables mediate the relationship between hypothermia and POCD. We searched the Web of Science, PubMed database, Scopus, and the Cochrane Library database (up to June 2017), and systematically reviewed a list of retrieved articles. Our final review includes only randomized controlled trials (RCTs) that compared administration of hypothermia (34°C). Statistical analysis of the risk ratio (RR) and corresponding 95% confidence interval (95% CI) was used to report the overall effect. Mantel-Haenszel risk ratio (MH RR) and corresponding 95% CI was used to report the overall effect and meta-regression analysis. Eight RCTs were included in this study, with a total of 1,474 patients. The POCD occurred in 36.06% of all cases. A wide range of hypothermia (28-34°C) did not reduce the occurrence of POCD (RR = 0.983 (95% CI = 0.881-1.143); Z = -0.304; P = 0.761; I2 = 38%). Shorter CPB time reduced the occurrence of POCD (MH log risk ratio = -0.011 (95% CI = -0.021--0.0008); Z = -2.123; P = 0.033). Postoperative cognitive deficit is a common event among CABG patients. Contrary to deep hypothermia, mild hypothermia was significantly effective in reducing the risk of POCD. The neuroprotective effect of hypothermia on POCD may be attenuated by prolonged cardiopulmonary bypass (CPB) time.