Mild hypothermia during isoflurane anesthesia decreases resistance to E. coli dermal infection in guinea pigs

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Abstract
Small changes in core temperature profoundly alter cutaneous blood flow, a major factor influencing resistance to wound infection. Furthermore, when measured in vitro, various immune functions are temperature dependent in the physiological range. Accordingly, we tested the hypothesis that mild hypothermia impairs and mild hyperthermia improves resistance to dermal infections. Thirty–two guinea pigs were anesthetized for 6 h using 1.5% (1.25 MAC) inspired isoflurane. Their core temperatures were maintained at either 39˚C (normal for guinea pigs, n= 11), 36˚C (n = 12), or 41˚C (n = 9). One h after induction of anesthesia, 2times108 E.coli were injected intradermally with a 26–g needle at eight sites on each animal's back. Core temperatures were not controlled after recovery from anesthesia, and animals in each group were maintained in the same environment. Twenty–four h after injection, the area of induration surrounding each injection site was measured. This is a standard test of resistance to wound infection. Values were compared using one–way ANOVA and Scheffe's S tests. Results are presented as means ± standard deviations; differences were considered significant when P < 0.05. Areas of inflammation on the hypothermic animals were significantly larger (48± 10 mm2) than those on normothermic (36± 10 mm2) or hyperthermic (37 ± 6 mm2) animals. These data suggest that mild hypothermia during anesthesia significantly impairs resistance to dermal infection. In contrast, mild hyperthermia does not appear to be protective.