The Effects of Mild Perioperative Hypothermia on Blood Loss and Transfusion Requirement

BACKGROUND: Anesthetic-induced hypothermia is known to reduce platelet function and impair enzymes of the coagulation cascade. The objective of this meta-analysis and systematic review was to evaluate the hypothesis that mild perioperative hypothermia increases surgical blood loss and transfusion requirement. METHODS: The authors conducted a systematic search of published randomized trials that compared blood loss and/or transfusion requirements in normothermic and mildly hypothermic (34-36 degrees C) surgical patients. Results are expressed as a ratio of the means or relative risks and 95% confidence intervals (CI); P < 0.05 was considered statistically significant. RESULTS: Fourteen studies were included in analysis of blood loss, and 10 in the transfusion analysis. The median (quartiles) temperature difference between the normothermic and hypothermic patients among studies was 0.85 degrees C (0.60 degrees C versus 1.1 degrees C). The ratio of geometric means of total blood loss in the normothermic and hypothermic patients was 0.84 (0.74 versus 0.96), P = 0.009. Normothermia also reduced transfusion requirement, with an overall estimated relative risk of 0.78 (95% CI 0.63, 0.97), P = 0.027. CONCLUSION: Even mild hypothermia (<1 degree C) significantly increases blood loss by approximately 16% (4-26%) and increases the relative risk for transfusion by approximately 22% (3-37%). Maintaining perioperative normothermia reduces blood loss and transfusion requirement by clinically important amounts.