Does moderate hypothermia really carry less bleeding risk than deep hypothermia for circulatory arrest? A propensity-matched comparison in hemiarch replacement

Background Moderate (MHCA) versus deep (DHCA) hypothermia for circulatory arrest in aortic arch surgery has been purported to reduce coagulopathy and bleeding complications, although there are limited data supporting this claim. This study aimed to compare bleeding-related events after aortic hemiarch replacement with MHCA versus DHCA. Methods Patients who underwent hemiarch replacement at a single institution from July 2005 to August 2014 were stratified into DHCA and MHCA groups (minimum systemic temperature ≤20°C and >20°C, respectively) and compared. Then, 1:1 propensity matching was performed to adjust for baseline differences. Results During the study period, 571 patients underwent hemiarch replacement: 401 (70.2%) with DHCA and 170 (29.8%) with MHCA. After propensity matching, 155 patients remained in each group. There were no significant differences between matched groups with regard to the proportion transfused with red blood cells, plasma, platelet concentrates, or cryoprecipitate on the operative day, the rate of reoperation for bleeding, or postoperative hematologic laboratory values. Among patients who received plasma, the median transfusion volume was statistically greater in the DHCA group (6 vs 5 units, P = .01). MHCA also resulted in a slight reduction in median volume of blood returned via cell saver (500 vs 472 mL, P < .01) and 12-hour postoperative chest tube output (440 vs 350, P < .01). Thirty-day mortality and morbidity did not differ significantly between groups. Conclusions MHCA compared with DHCA during hermiarch replacement may slightly reduce perioperative blood-loss and plasma transfusion requirement, although these differences do not translate into reduced reoperation for bleeding or postoperative mortality and morbidity.