Blackwell Publishing Journal Backfiles 1879-2005
Because various immune functions are impaired at temperatures only 1° to 3° C less than normal, we tested the hypothesis that mild hypothermia during anesthesia impairs resistance to dermal infections. Guinea pigs were anesthetized for 6 hours with 1% inspired halothane. Their core temperatures were maintained at either 39° C (normal for guinea pigs, n = 12) or 36° C (n = 12). Two hours after induction of anesthesia, three doses each of Staphylococcus aureus (108, 107, and 106 organisms) were injected intradermally at nine sites on each animal's back. Core temperatures were not controlled after recovery from the anesthetic, and animals in each group were maintained in the same environment. Four days after anesthesia, each injection site was excised to obtain a count of viable bacteria. Subcutaneous oxygen partial pressure values, averaged over time, were 53 ± 3 mm Hg (mean ± SEM) in the hypothermic group and 62 ± 4 mm Hg in the normothermic group (p = 0.06). Capillary perfusion, as assessed by laser Doppler flowmetry, was comparable in the two groups. One day after injection of 108 bacteria, the area of induration was 89 ± 11 mm2 in the hypothermic group but only 61 ± 6 mm2 in the normothermic group (p 〈 0.05). On postanesthetic day 4, the area of induration was 72 ± 6 and 59 ± 6 mm2 in the hypothermic and normothermic groups, respectively (p 〉 0.05). After inoculation with 108 bacteria, the fraction recovered was 1.0 ± 0.2 in the hypothermic groups and 0.6 ± 0.2 in the normothermic group (p 〈 0.05). After inoculation with 107 and 106 bacteria, the fraction recovered was less than 0.2, and no difference was found between the hypothermic and normothermic animals. Thus mild hypothermia during halothane-induced anesthesia slightly impairs resistance to dermal infection.
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