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Thyroid hormones homeostasis in pediatric patients during and after cardiopulmonary bypass
1Institute of Clinical Physiology, National Research Council, Pisa, Italy.
Insights
Pediatric cardiopulmonary bypass significantly reduces thyroid hormones, including total triiodothyronine and thyroxine. These hormone changes persist post-surgery, indicating altered thyroid function in pediatric patients.
Area of Science:
- Pediatric Endocrinology
- Cardiovascular Surgery
- Thyroid Hormone Metabolism
Background:
- Cardiopulmonary bypass (CPB) is a critical procedure in pediatric cardiac surgery.
- Thyroid hormone levels can be affected by major surgical stress and physiological changes.
- Understanding these effects is crucial for managing pediatric patients undergoing CPB.
Purpose of the Study:
- To investigate the impact of CPB on thyroid hormone concentrations in pediatric patients.
- To analyze the temporal changes in thyroid hormones and thyroid-stimulating hormone (TSH) before, during, and after CPB.
- To determine if CPB-induced alterations in thyroid function persist in the postoperative period.
Main Methods:
- Measurement of total triiodothyronine (TT3), total thyroxine (TT4), free triiodothyronine (FT3), free thyroxine (FT4), and TSH in 14 pediatric patients.
- Serial blood sampling before, during, and up to 7 days after CPB.
- Patients underwent CPB with varying degrees of hypothermia based on their condition.
Main Results:
- A significant reduction in TT3, TT4, FT3, FT4, and TSH was observed during and after CPB.
- Hormone levels reached their nadir between 12 and 48 hours post-CPB.
- TSH normalized by postoperative day 3, but TT3 and FT3 remained suppressed for 7 days, suggesting impaired thyroxine to triiodothyronine conversion.
Conclusions:
- Pediatric patients undergoing CPB exhibit significant alterations in thyroid hormone metabolism, similar to adults.
- These changes are exacerbated postoperatively and persist for at least 7 days.
- The precise mechanisms remain unclear, and the role of triiodothyronine replacement therapy is controversial.
Abstract:
The concentrations of thyroid hormones were measured in 14 pediatric patients before, during, and after cardiopulmonary bypass. The ages of the 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 triiodothyronine, and thyroid-stimulating hormone, and in the ratio of free triiodothyronine 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 thyroid function and in the conversion of thyroxine to triiodothyronine are 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 reduced versus its baseline values (24% +/- 0.13%), despite low levels of both total (40% +/- 18%) and free (39% +/- 20%) triiodothyronine: it returned to its preoperative level by the third postoperative day, but both the total (75% +/- 10%) and free (74% +/- 3%) triiodothyronine levels remained below their baseline values for 7 days postoperatively. Neither hemodilution nor hypothermia was responsible for the alteration observed. We conclude that pediatric patients undergoing cardiopulmonary bypass manifest changes in hormone metabolism similar to those seen in adult patients. These changes increase progressively during the postoperative period, and are still present 7 days postoperatively. The exact mechanism responsible for causing these changes is not thoroughly understood. Whether triiodothyronine replacement therapy is beneficial or deleterious remains controversial.