Perfusion temperature, thyroid hormones and inflammation during pediatric cardiac surgery.

OBJECTIVES: During cardiopulmonary bypass (CPB) surgery there are several alterations in concentrations of thyroid hormones. Although hypothermia and inflammation have been implicated in the disturbed thyroid axis during CPB, these issues are far from clear.

METHODS AND RESULTS: We measured serum/plasma concentrations of thyroid hormones and inflammatory mediators in children with body weight <10 kg, undergoing open heart surgery, randomized to mild (n=15, 32 degrees C) or moderate (n=15, 25 degrees C) hypothermia. During CPB there was a marked decrease in triiodothyronine (T3), free thyroxin (FT4) and thyroid-stimulating hormone (TSH), followed by a slight increase after 24 h, but without normalization 48 h after CPB. There was no difference in the thyroid response between the two hypothermia groups. During CPB the maximal changes in plasma levels of interleukin (IL)-6 and the chemokines, regulated on activation normal T cell expressed and secreted (RANTES) and monocyte chemoattractant protein (MCP)-1 were inversely correlated with the maximal changes in serum levels of T3.

CONCLUSION: Our findings in this randomized trial do not support a role for hypothermia as a major cause of altered thyroxin responses in children undergoing CPB. Our finding may also suggest that in addition to IL-6, other inflammatory cytokines, such as chemokines, should be further investigated for their possible influence on the thyroid axis during CPB.