Perioperative hypothermia is a common and serious complication during anesthesia and surgery [1] [2]. Even mild perioperative hypothermia is associated with major complications such as increased incidence of postoperative wound infections [3], coagulopathy [4], and myocardial ischemia [5]. The understanding of perioperative thermal perturbations and their consequences led to the development of optimal prevention and treatment strategies, and maintaining normothermia is now clinical standard. The efficacy of available patient warming systems depends on numerous factors, including the type of heat transfer, device design, and the location and amount of skin available for heat exchange.

Not only the avoidance of perioperative hypothermia but furthermore postoperative local warming of wounds increases subcutaneous oxygen tension and collagen synthesis, thus might improve wound healing and decrease the rate of postoperative wound infections.(6) This is of special importance in specific critical patient populations such as the obese patients and patients undergoing abdominal and cardiac surgery.

Fever-range whole body hyperthermia (FR-WBH) has not yet been used in the perioperative and intensive care setting but has interesting potential, especially when used pre-operatively as “thermal preconditioning” in order to induce certain immune responses. It increases the activity of several facets of the immune system. Fever is an extremely complex physiologic response encompassing multiple elements, including cytokine induction, generation of acute phase proteins, and activation of endocrine and nervous systems, all apparently related to increased body temperature [7]. Hughes et al. observed that mild whole-body heating resulted in a notable reorganization of the cytoskeleton of both splenic T and B lymphocytes [8]. Furthermore, it was shown that fever-range heat treatments can enhance the adhesion of leukocytes to high endothelial venules by augmenting the avidity of L-section and the integrin α4β7 in an Interleukin 6 (IL-6) dependent manner [9]. These effects provide strong mechanistic evidence that heat is able to induce highly selective molecular changes in immune effector cells that may enhance their ability to home to sites of inflammation or tumors. Elevating core temperature preoperatively to 38.5°C – 39.5°C (thermal preconditioning) can induce heat shock proteins (HSP-35, -70, -72), thereby improving immunologic host defense, especially in surgical cancer patients prone to intraoperative contamination and infection.

In addition, FR-WBH influences the number and activity of natural killer (NK) cells, altering their cell shape by the interaction of HSP 70 with spectrins and PKC in an ATP dependent manner which leads to an altered leukocyte—endothelium interaction by an increase of L-selectin [9]. HSPs also directly induce CD 14 receptors on monocytes. Mild hyperthermia (38.5 – 39.5°C) over one hour should be sufficiently effective and is well-tolerated in contrast to longer and higher hyperthermia levels [10].

Surgery causes a series of immune and inflammatory reactions, which can be summarized as the surgical stress response. The surgical stress response depends on type and extent of surgery. Most of the postoperative complications can be attributed to the surgical stress response. Anaesthesia seeks to diminish surgical stress response and the inflammatory cascade assoiciated with it. This improves outcome of patients undergoing surgery A novel approach is the activation of the immune system before surgery, “pre-conditioning”, which might alter the surgical stress response and the inflammatory cascade during and after surgery and thus improve patient outcome. We have so far tested the feasibility of the whole body warming system heckel – HT2000M. Further research will be needed to test the effect of preoperative warming on the immune system and outcome of surgical patients.