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Hypothalamic-Pituitary-Thyroid Axis Changes in Children after Cardiac Surgery

Departments of Pediatrics (S.D.M., C.H., I.M.R., R.M.C.) and Surgery (I.M.R.), University of Alberta, Edmonton, Alberta, Canada T6G 2B7

Address all correspondence and requests for reprints to: Dr. Seth D. Marks, Department of Pediatrics, Division of Endocrinology, University of Alberta, Stollery Children’s Hospital, 1C4 Walter Mackenzie Health Sciences Centre, 8440 112th Street, Edmonton, Alberta, Canada T6G 2B7. E-mail: smarks{at}ualberta.ca.

Introduction: Hypothalamic-pituitary-thyroid axis changes in critical illness result in nonthyroidal illness syndrome (NTIS) characterized by abnormal TSH and thyroid hormone levels. It is unclear whether NTIS is adaptive or maladaptive. Some have suggested that NTIS adversely affects outcome, but there are limited data in children.

Objective: Our objective was to determine the natural history of NTIS in children undergoing cardiac bypass surgery and to correlate these changes with outcome and illness severity.

Methods: Thyroid function was measured in 21 patients, aged 1–11 yr, preoperatively and postoperatively twice daily on postoperative days (POD) 0–3 and daily thereafter until POD 7. Pediatric Logistic Organ Dysfunction and inotrope scores and pediatric intensive care unit, hospital, and ventilation days were measured and statistically analyzed in relation to thyroid function.

Results: All patients exhibited NTIS within the first day postoperatively. TSH recovered by POD 4. Total T₃, free T₃ index, and T₃ uptake were still below preoperative levels on POD 7. NTIS changes correlated to prolonged hospital stays with increased pediatric intensive care unit and mechanical ventilation days and also showed strong relations with Pediatric Logistic Organ Dysfunction and inotrope scores. The T₃ measures drawn within 6–14 h from surgery were predictive of clinical outcome. Alterations in illness severity preceded changes in thyroid function.

Conclusion: NTIS was present in this population of critically ill children with some of the biochemical changes not corrected by 8 d postoperatively. The degree of NTIS was related to and predictive of clinical outcome and illness severity.