Improvement of Host Defense Influence of Body Temperature
Mild hypothermia in the range of 34 to 36°C has a large number of adverse effects including increased blood loss and transfusion requirements (SDC-190), prolonged postanesthesia recovery (SDC-191), prolonged hospitalization (SDC-191-192), an increase in morbid myocardial events (SDC-192-194) and an increase in wound infections (SDC-195). Hypothermia is especially common in patients with trauma (SDC-196).
The effect of mild hypothermia on the development of wound infections has been studied particularly well in patients undergoing colorectal surgery. In one double-blinded study, 200 patients were randomly assigned to either a group which was managed with hypothermia or to a group managed with normothermia. Surgical wound infections occurred in 19% of the hypothermic patients compared to 6% of normothermic patients, and length of hospitalization was increased in hypothermic patients, further affecting cost. In another study involving patients with colon resection, hypothermia tripled the incidence of wound infection (SDC-193). Maintaining normothermia is also important in clean surgeries of short duration. Four hundred twenty-one patients having breast, varicose vein, or hernia surgeries were randomly assigned to a standard nonwarmed group or to two warmed groups, which had local and systemic warming (SDC-197). Nonwarm patients had a 14% incidence of wound infection compared to 5% with warming. These findings were supported by another study of 290 surgical patients (SDC-198) where wound infections occurred in 11.5% of those with hypothermia compared to 2% with normothermia (relative risk 6.3). It has been reported that local warming with radiant heat was as good as systemic warming in preventing SSI (SDC-199).
Numerous reasons for the adverse effects of hypothermia have been advanced. The most important of these is that hypothermia causes generalized vasoconstriction, which decreases subcutaneous blood flow and oxygen tension (14, SDC-195, SDC-200). Hypothermia also has adverse effects on antibody and cell-mediated immune defenses (SDC-193) and cytokine regulation (SDC-201).
Several studies are emerging, which indicate that hyperthermia may be even more beneficial than normothermia in preventing wound infections. In experimental animals, it has been shown that an increasing core temperature that occurs during bacterial infections is essential for optimal antimicrobial host defense (SDC-202). A recent study has shown that a number of critical immunological defense mechanisms are enhanced by hyperthermia up to 40°C in humans (SDC-201).
Hypothermia increases the development of wound infection because of adverse effects on the physiologic and immunologic functions necessary to kill contaminating bacteria. Studies have not yet been done to show whether the effects of mild hyperthermia/normothermia are additive or synergistic with the potential beneficial effects of hyperoxia, especially in either smokers or diabetic patients.
Annals of Surgery. 2011;253(6):1082-1093. © 2011 Lippincott Williams & Wilkins
Cite this: Updated Recommendations for Control of Surgical Site Infections - Medscape - Jun 01, 2011.