MILD INTRAOPERATIVE HYPOTHERMIA REDUCES PRODUCTION OF REACTIVE OXYGENINTERMEDIATES BY POLYMORPHONUCLEAR LEUKOCYTES

Mild hypothermia directly impairs numerous immune functions in vitro. However, the in vivo effects of mild hypothermia on neutrophil phagocy tosis and oxidative killing remain unknown. We tested the hypothesis t hat mild intraoperative hypothermia decreases neutrophil phagocytic ca pacity and generation of reactive oxygen intermediates (a measure of o xidative killing). Additionally, we evaluated the effects of ill vitro temperature manipulations on each function. Thermal management was ra ndomly assigned in 10 surgical patients, causing intraoperative core t emperatures to range from 33 to 37 degrees C. Production of reactive o xygen intermediates and neutrophil phagocytosis were evaluated using f low cytometry at ambient temperature. Phagocytic capacity was assessed by uptake of fluorescein isothiocyanate-labeled Escherichia coil. Rea ctive oxygen production was estimated by the intracellular conversion of dihydrorhodamine 123 to rhodamine 123. Blood samples were obtained preoperatively, 1 h after surgery started, and 2 h postoperatively. Bl ood was also obtained from 10 matched control subjects and tested at 3 2, 37, and 40 degrees C. Neutrophil oxidative and phagocytic capacitie s were significantly reduced intraoperatively, compared with preoperat ive and postoperative values. Intraoperative production of reactive ox ygen species was linearly related to core temperature. In contrast, th ere was no correlation between core temperature and phagocytic activit y. In vitro production of reactive oxygen intermediates increased sixf old from 32 to 40 degrees C. In vitro phagocytic capacity increased fo urfold in this temperature range. Production of oxidative intermediate s was most closely related to intraoperative core temperature, decreas ing nearly fourfold over a 4 degrees C range. This in vivo temperature dependence was matched in vitro. Impaired neutrophil oxidative killin g may contribute to the observed hypothermia-induced reduction in resi stance to infection.