Duration of Deep Hypothermia During Aortic Surgery and the Risk of Perioperative Blood Transfusion

Deep hypothermia, which is used during thoracic aortic surgery for neuroprotection, is associated with coagulation abnormalities in animal and in vitro models. However, there is a paucity of data regarding the impact of deep hypothermia duration on perioperative bleeding. The objective of the current study was to examine the relationship between the duration of deep hypothermia and perioperative bleeding. A retrospective review of 507 consecutive thoracic aortic surgery patients who had surgery with deep hypothermic circulatory arrest was performed. The degree of bleeding and coagulopathy was estimated using perioperative transfusion. Log linear modeling with Poisson regression was used to analyze the relationship between deep hypothermia duration and perioperative bleeding, while controlling for other preselected variables. There was a significant association between deep hypothermia duration and RBC transfusion (P = 0.001). There was no significant association between deep hypothermia duration and FFP and platelet transfusion (P = 0.18 and P = 0.06). The association between deep hypothermia duration and the amount of bleeding (RBC transfusion) was dependent on total CPB time. In general, for shorter CPB times (approximately 120 to 180 minutes) there was an upward sloping line or positive relationship between deep hypothermia duration and bleeding. However, for cases with longer CPB times (300 to 360 minutes), there was no such relationship. The relationship between deep hypothermia duration and perioperative bleeding is dependent on CPB time. For surgeries with short CPB times (120 to 180 minutes), prolonged deep hypothermia is associated with increased post-operative bleeding, as estimated by RBC transfusion. For cases with longer CPB times (300 to 360 minutes), there appears to be no relationship.