Aim
===

To investigate the effect of core temperature (T°) during CPB on leukocyte activation and cytokine production and to correlate those findings to postoperative organ damage in an animal experimental model.

Methods
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18 young pigs were randomly assigned to a T°- group during CPB: normothermia (T° 37°C; *n* = 6), mild hypothermia (T° 28°C; *n* = 6) and deep hypothermia (T° 20°C; *n* = 6). Leukocyte count and plasma levels of tumor necrosis factor (TNFα) were measured before, during and after CPB. At the end of the experimentation (6 h post-CPB), probes of heart, lungs, liver, kidney, and intestine were taken for histological examination.

Results
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There was a significant fall of leukocyte count at induction of CPB, without any intergroup difference. During and at the end of CPB, leukocyte count was significantly higher in group 37°C as compared with the other groups. At a later stage after CPB, group 20°C showed significantly higher leukocyte count than group 28°C and group 37°C, respectively. The course of neutrophils was similar.

TNF-α was not released in group 28°C neither during nor after CPB. By contrast, there was a significant production of TNF-α in groups 37°C and 20°C, the circulating levels being significantly higher in group 37°C. Histological examination showed that the most important tissue damage in terms of interstitial edema and leukostasis in heart, lung, liver, kidney, and small intestine was seen in group 37°C followed by group 20°C while the least important damage was present in group 28°C.

Conclusion
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CPB-induced postoperative organ damage, probably related to leukocyte activation and TNF-α production, is highest in pigs operated on in normothermia and lowest in those operated on in mild hypothermia.
