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.