Thyroid function in neonates with severe respiratory failure on extracorporeal membrane oxygenation

The object was to study thyroid function in neonates with severe respirator y failure on extracorporeal membrane oxygenation (ECMO) and determine wheth er abnormal thyroid function correlates with prognosis. Total and free thyr oxine (T-4, FT4), total and free triiodothyronine (T-3, FT3), reverse triio dothyronine (rT(3)), thyroid-stimulating hormone, and thyroxine binding glo bulin were measured in 14 newborn infants with severe respiratory failure ( age 1-30 days) from samples collected before anesthesia for cannula placeme nt, at 30, 60, and 360 min after initiation of ECMO, and on days 2, 4, 6, a nd 8. The patients were divided into survivors and non-survivors for statis tical analyses. No differences were noted between survivors and nonsurvivor s in the pre-ECMO mean serum concentrations of the thyroid function tests a nalyzed. In nine survivors, mean serum T-4, FT4, T-3, FT3, and rT(3) all de clined significantly within 30-60 min after initiation of ECMO, compared to baseline values. The values for all mean serum concentrations recovered co mpletely and exceeded baseline between days 2 and 8. In five non-survivors, the decline of all mean serum values was not statistically significant and recovery to baseline was not achieved. The ratios of mean serum concentrat ion of rT(3)/FT3 were significantly different between survivors and non-sur vivors across all times during the ECMO course (p<0.0005). These findings i ndicate that abnormalities in thyroid function occur in neonates with sever e respiratory failure on ECMO and that the rT(3)/FT3 ratio correlates with prognosis over the ECMO course. Survival was associated with a significant reduction of serum thyroid hormone concentrations followed by recovery. We speculate that, in neonates with respiratory failure on ECMO, adaptive mech anisms which enhance survival include the capacity to down-regulate the pit uitary-thyroid axis.