THYROID-HORMONES HOMEOSTASIS IN PEDIATRIC-PATIENTS DURING AND AFTER CARDIOPULMONARY BYPASS

The concentrations of thyroid hormones were measured in 14 pediatric p atients before, during and after cardiopulmonary bypass. The ages of t he patients ranged between 18 months and 14 years. Patients were kept normothermic, or moderate or deep hypothermia was induced depending on the specific pathologic condition involved. A marked reduction in the levels of total triiodothyronine, total thyroxine, free triiodothyron ine, and thyroid-stimulating hormone, and in the ratio of free triiodo thyronine to free thyroxine was detected during the time frame of the study. The minimum levels of each hormone were reached between 12 and 48 hours after cardiopulmonary bypass, indicating that changes in thyr oid function and in the conversion of thyroxine to triiodothyronine ar e triggered by cardiopulmonary bypass and represent specific phenomena , and that these changes are progressively exacerbated during the post operative period. The thyroid-stimulating hormone level was markedly r educed versus its baseline values (24% +/- 0.13%), despite low levels of both total (40% +/- 18%) and free (39% +/- 20%) triiodothyronine: i t returned to its preoperative level by the third postoperative day, b ut both the total (75% +/- 10%) and free (74% +/- 3%) triiodothyronine levels remained below their baseline values for 7 days postoperativel y. Neither hemodilution nor hypothermia was responsible for the altera tion observed. We conclude that pediatric patients undergoing cardiopu lmonary bypass manifest changes in hormone metabolism similar to those seen in adult patients. These changes increase progressively during t he postoperative period, and are still present 7 days postoperatively. The exact mechanism responsible for causing these changes is not thor oughly understood. Whether triiodothyronine replacement therapy is ben eficial or deleterious remains controversial.