Effects of mild perioperative hypothermia on cellular immune responses

Background: Unintentional perioperative hypothermia is a common complication of anesthesia and surgery associated with adverse effects on several systems, including impaired wound healing and more frequent wound infections. Mild hypothermia affects various immune functions. In the current study, the authors sought to determine whether immune alterations in the perioperative period might be induced, at least in part, by impaired thermoregulation during this period. Methods: Sixty patients undergoing abdominal surgery were randomly assigned to two thermal care groups: routine care or forced-air warming. The patients' anesthetic care was standardized. Venous blood samples were collected 90 min before induction of anesthesia and immediately, 24 h, and 48 h after surgery. White cells were separated and frozen. Peripheral blood mononuclear cells were used to test cytokine production (interleukins [IL] -1β, -2, and -6; tumor necrosis factor-α [TNF-α]), mitogens-induced proliferation, and natural killer INK cell cytotoxicity. Plasma cortisol levels were also determined. Results: Patients in the normothermia group maintained normal body core temperature, whereas temperature decreased by approximately 1°C in the hypothermia group. Mitogenic responses were suppressed in cells from patients in the hypothermia but not in the normothermia group 24 and 48 h after surgery. Proinflammatory cytokine (IL-1β, IL-6, TNF-α) production increased in both groups, although the production of IL-1β was significantly higher in the normothermia group 24 h after surgery. Production of IL-2 was suppressed in the hypothermia but not in the normothermia group at 24 h. Conclusions: MHd perioperative hypothermia suppressed mitogen-induced activation of lymphocytes and reduced the production of certain cytokines, IL-1β and IL-2, and in this way may contribute to the immune alterations observed in the perioperative period.