Hypothermia Increases Blood Loss During Surgery

A new study offers convincing evidence that even mild hypothermia during surgery increases blood loss significantly, as well as transfusion requirement.

Researchers at The Cleveland Clinic (OH, USA) conducted a systematic search of randomized trials published between 1966 and 2006 that compared blood loss and transfusion requirements in normothermic and mildly hypothermic (34-36 ºC) surgical patients, and analyzed the results. Results were expressed as a ratio of the means--or relative risks--and 95% confidence intervals (CI). In all, 14 studies were included in analysis of blood loss, and 10 in the transfusion analysis.

The results showed that the median temperature difference between the normothermic and hypothermic patients among studies was 0.85 ºC (0.60 ºC versus 1.1 ºC). The ratio of geometric means of total blood loss in the normothermic and hypothermic patients was 0.84 (0.74 versus 0.96). Normothermia also reduced transfusion requirement, with an overall estimated relative risk of 0.78. The findings indicate that even mild hypothermia (less than 1 ºC) significantly increases blood loss by approximately 16%, and increases the relative risk for transfusion by approximately 22%. The study was published in the January 2008 issue of the journal Anesthesiology.

"When all the studies were evaluated together, the results clearly show that even very mild hypothermia increases blood loss and transfusion requirements by clinically important amounts,” concluded lead author Daniel I. Sessler, M.D., and colleagues.

All anesthetics interfere with the systems that naturally regulate body temperature; consequently, body temperature decreases in surgical patients who are not actively warmed. Hypothermia has long been known to increase the risk of heart attacks adverse myocardial events and infection, and prolongs recovery from surgery. However, anesthesiologists and the physicians responsible for monitoring patients' vital signs during surgery are able to control temperature easily, at low cost, and with virtually no risk to patients.


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