Relationship between changes in thyroid hormone level and severity of the postoperative course in neonates undergoing open-heart surgery

Background: Our aim was to determine whether the changes in thyroid function after open-heart surgery in neonates depend on the postoperative course. Methods: Twenty neonates undergoing open-heart surgery for congenital heart disease were prospectively studied in the cardiac intensive care unit of a university-affiliated children's hospital. The patients were divided into two groups by level of inotropic support (high or mild). Results: The groups were similar in age, bypass time and ultrafiltration volume. In both groups, there was a significant reduction in levels of thyroid-stimulating hormone and FT₄ at 24 h postoperatively. However, in the high inotropic support group, FT₄ was lower for a longer time. This group also had a significantly higher score on The Pediatric Risk of Mortality (PRISM; P < 0.042) and a longer duration of ventilation (P < 0.014). Conclusions: Neonates after open-heart surgery undergo changes in thyroid function characteristic of euthyroid sick syndrome. The degree of hypothyroxinemia may be related to the severity of illness and the postoperative course.