Journal: Anesthesiology 108(1):71-77, 2008. 49 References
Reprint: Department of OUTCOMES RESEARCH, Cleveland Clinic, P77, Cleveland, OH 44195 (D Sessler, MD)
Faculty Disclosure: Abstracted by R. Ouellette, who has nothing to disclose.
Anesthetic-induced thermoregulatory impairment produces hypothermia in unwarmed surgical patients. Hypothermia results initially from an internal core-to-peripheral redistribution of body heat and subsequently from heat loss exceeding metabolic heat production. Prospective trials indicate that even mild hypothermia causes severe complications including morbid myocardial outcomes, surgical wound infection, prolonged recovery and hospitalization, nitrogen balance, shivering, and thermal discomfort. Hypothermia impairs platelet function, primarily by impairing release of thromboxane A2, which is necessary for formation of an initial platelet plug. Hypothermia also impairs function of enzymes in the coagulation cascade.
Whether mild perioperative hypothermia causes a clinically important coagulopathy remains controversial. This systematic review and meta-analysis evaluates the hypothesis that mild perioperative hypothermia increases surgical blood loss and transfusion requirement. Medical literature published since 1966 was searched in all languages. Traditional meta-analysis methods were used to assess the comparative effect of normothermia, versus hypothermia on both total blood loss and whether a patient received any transfusion.
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°C (0.60ºC vs. 1.1ºC). The ratio of geometric means of total blood loss in the normothermic and hypothermic patients was 0.84 (0.74 vs. 0.96). Normothermia also reduced transfusion requirement with an overall estimated relative risk of 0.78 (95% CI 0.63, 0.97).
This analysis, based on the available literature, indicates that even mild hypothermia significantly increases blood loss by an estimated 16%. Although not an enormous treatment effect, these data add to other studies that demonstrate that preventing hypothermia decreases the risk of many other complications and is thus indicated for reasons other than reducing blood loss.
These results are consistent with this theory: mild hypothermia significantly increased the relative risk for transfusion by approximately 22%. Maintaining perioperative normothermia reduces blood loss and transfusion requirement by clinically important amounts. |
