Interleukin-6 and thyroid hormone metabolism in pediatric cardiac surgery patients

Pediatric patients undergoing cardiac surgery have been reported to have low serum triiodothyronine (T-3) levels in the postoperative period. The cause of this dysfunction is not known, although proinflammatory cytokines such as interleukin-6 (IL-6) have been implicated in the inhibition of hepatic conversion of thyroxine (T-4) to T-3. This study measured serum levels of IL-6 and T-3 during the first 4 postoperative days in 16 children (mean age, 28 +/- 7 days) undergoing cardiopulmonary bypass surgery. The mean preoperative serum total T-3 level was 164 +/- 30 ng/dL (2.5 +/- 0.5 nmol/L) that decreased significantly to a nadir of 43 +/- 8 ng/dL (0.6 +/- 0.01 nmol/L) within 48 hours after surgery. Serum IL-6 levels increased significantly from 16 +/- 7 pg/mL preoperatively to a peak value of 374 +/- 134 pg/mL measured 2-3 hours after surgery. A positive correlation (r(2) = 0.507) was found between the peak serum level of IL-6 and the lowest serum T-3 level in each patient attained during the 4 postoperative days. Potential treatments directed toward diminishing the rise in proinflammatory cytokines in the immediate postoperative period may prove effective in preventing the low serum T-3 in children undergoing cardiac surgery, and thus diminish the associated postoperative morbidity.