Changes in thyroid hormone concentrations during neonatal extracorporeal membrane oxygenation

Thyroid hormone concentrations can be disturbed during critical illness. Our aim was to determine changes in thyroid hormone concentrations during neonatal extracorporeal membrane oxygenation (ECMO).

We included 21 ECMO-treated neonates. Age-specific s.d. scores (SDS) of free and total thyroxine (FT4; TT4), reverse and total triiodothyronine (rT3; TT3), thyroid-stimulating hormone (TSH) and thyroxine-binding globulin (TBG) were determined at six fixed time-points. Data were analyzed using general linear models.

At baseline, mean SDS FT4 (-0.78, 95% CI: -1.37 to -0.19), TT4 (-1.97, 95% CI: -2.76 to -1.18), TT3 (-0.88, 95% CI: -1.13 to -0.63), TSH (-2.14, 95% CI: -2.93 to -1.35) and TBG (-3.52, 95% CI: -4.55 to -2.50) were low with high mean SDS rT3 (0.53, 95% CI: 0.28 to 0.78). One hour after start ECMO, TT4, TSH and TBG had further declined; 12 h after start ECMO TT3 had declined (all P<0.05). After this decline, mean SDS TSH increased to the baseline level 12 h after start ECMO (-2.50, 95% CI: -3.22 to -1.79), and was higher than baseline 48 h after start ECMO (-0.56, 95% CI: -1.29 to 0.17). This TSH increase was followed by increases in TT4 and TT3. FT4 remained constant within the normal range during ECMO.

Thyroid hormone concentrations before ECMO were suggestive of non-thyroidal illness syndrome (NTIS). During ECMO, increases in TSH, TT4 and TT3 after an initial decline possibly reflect spontaneous restoration of the hypothalamic-pituitary-thyroid axis. FT4 remained constant within the normal range. This suggests that thyroxine therapy is not required during ECMO.