Short passive cooling protects rats during hepatectomy by inducing heat shock proteins and limiting the induction of pro-inflammatory cytokines.

BACKGROUND: Prolonged hepatic warm ischemia during surgery remains a significant problem, particularly in the setting of liver resection and reduced remaining liver mass. The goal of the present study is to evaluate the effect of passive cooling caused by exposure to ambient conditions on hepatic injury in rats during warm ischemia followed by hepatectomy.
METHODS: The left and median lobes of male rats were exposed to 75 min of ischemia under either normothermic (37 degrees C) or mildly hypothermic (34 degrees C) conditions. After 75 min of ischemia, the right lobe was resected, leaving the animal with only the remaining ischemic lobes. Animals were allowed to survive indefinitely or sacrificed at 4 h after reperfusion for determination of injury and inflammatory gene expression.
RESULTS: Survival was already markedly higher in mildly hypothermic rats than normothermic rats at 24 h. Short passive cooling for the time course of the ischemic event significantly increased the hepatic induction of heat shock proteins 70 and 32 (both 3-fold versus normothermia, P<0.05) in response to ischemia/reperfusion whereas it significantly decreased the induction of tumor necrosis factor-alpha (TNF-alpha) and macrophage inflammatory protein-2 (MIP-2) in the liver. Biochemical markers of hepatic injury were significantly lower in the passive cooling group than in normothermic animals: aspartate aminotransferase (AST) serum concentrations were 9277+/-3461IU/L versus 15106+/-4104IU/L (P<0.01), and alanine aminotransferase (ALT) levels 5986+/-2246IU/L versus 9429+/-3643IU/L (P<0.01).
CONCLUSION: We demonstrated in a clinically relevant model of hepatic ischemia/reperfusion that mild hypothermia significantly reduces hepatic injury and improves survival.