Depressed thyroid function following paediatric cardiopulmonary bypass: association with interleukin-6 release?

Cellular activation with release of cytokines such as interleukin-6 (IL-6) occurs during cardiopulmonary bypass. IL-6 regulates a number of physiologic processes, and a possible role of IL-6 was recently postulated in the pathogenesis of changes in serum thyroid hormone concentrations in patients with nonthyroidal illness. The perioperative concentrations of triiodothyronine (T3) and IL-6 were determined in ten children undergoing open-heart surgery. Significant fall in T3 concentration was found postoperatively, while IL-6 increased significantly, peaking 2 hours postoperatively. The total accumulated IL-6 level 2 hours postoperatively was correlated to postoperative T3 concentration. A significant inverse correlation was found between T3 levels 24 and 48 hours postoperatively and total accumulated IL-6, and also between the percentage decrease in T3 concentrations and total accumulated IL-6. IL-6 release thus correlated inversely to T3 levels after cardiopulmonary bypass.