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The effects of cardiopulmonary bypass on thyroid function in infants weighing less than five kilograms
I M Mitchell1, J C Pollock, M P Jamieson
1Department of Cardiac Surgery, Royal Hospital for Sick Children, Glasgow, United Kingdom.
Insights
Cardiopulmonary bypass significantly impacts thyroid hormones in infants, causing substantial drops in triiodothyronine and thyroxine. These thyroid function changes differ from adults and may indicate hypothalamopituitary issues in critically ill infants.
Area of Science:
- Pediatric Endocrinology
- Cardiovascular Surgery
- Metabolic Regulation
Background:
- Triiodothyronine regulates cellular metabolism and has potential inotropic applications.
- Thyroid hormone levels are crucial for infant development and physiological stability.
Purpose of the Study:
- To investigate the impact of cardiopulmonary bypass on thyroid function in infants under 5 kg.
- To compare infant thyroid function changes with adult responses post-cardiopulmonary bypass.
Main Methods:
- Serial measurements of triiodothyronine, thyroxine, and thyroid-stimulating hormone in 10 infants.
- Correction for hemodilution effects during cardiopulmonary bypass.
- Analysis of hormone level changes over 7 days post-surgery.
Main Results:
- Significant decreases in triiodothyronine (78%) and thyroxine (57%) observed at 48 hours post-bypass.
- Thyroid-stimulating hormone levels showed inverse changes, preceding and mirroring thyroid hormone fluctuations.
- Hormone levels normalized between 5 to 7 days in most infants.
- Two non-survivors and one infant with a difficult recovery showed blunted thyroid hormone and TSH responses, suggesting hypothalamopituitary dysfunction.
Conclusions:
- Cardiopulmonary bypass induces profound, distinct thyroid function alterations in infants compared to adults.
- Post-bypass thyroid hormone dynamics in infants may serve as indicators of hypothalamopituitary axis integrity.
- Abnormal thyroid hormone regulation post-bypass in critically ill infants warrants further investigation into hypothalamopituitary function.
Abstract:
Triiodothyronine is an important regulator of cellular metabolism and may have potential use as an inotropic agent. The aim of this study was to determine the effects of cardiopulmonary bypass on thyroid function in infants weighing less than 5 kg. Serial measurements of triiodothyronine, thyroxine, and thyroid-stimulating hormone were made in 10 infants and corrected for the effects of hemodilution. We demonstrated a fall in triiodothyronine and thyroxine levels, with some recovery after 3 to 6 hours. An additional decrease then occurred, reaching a trough at 48 hours (representing a fall of 78% for triiodothyronine and 57% for thyroxine) before hormone levels returned to normal at 5 to 7 days. Thyroid-stimulating hormone concentrations increased and decreased, predating and complementing exactly the changes in triiodothyronine and thyroxine. These results are quantitatively and, for thyroid-stimulating hormone, qualitatively different from those previously reported in adults. In two patients who died, however, and in one who had a particularly difficult postoperative course, no increase in triiodothyronine, thyroxine, or thyroid-stimulating hormone concentrations was found after a trough had been reached at 48 to 72 hours, which suggests abnormal function at the hypothalamopituitary level.
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