Increased Thyroxin During Therapeutic Hypothermia Predicts Death in Comatose Patients After Cardiac Arrest

Background: The course and prognostic value of pituitary-thyroid axis hormones is not well studied after cardiac arrest. We aimed to study the prognostic role of the pituitary-thyroid axis response to resuscitation from cardiac arrest before, during and after therapeutic hypothermia. Methods: We conducted a retrospective cohort study in consecutive comatose patients after out-of-hospital cardiac arrest who were sampled before, during and up to 48 h after a 24-h period of therapeutic hypothermia in the intensive care unit (ICU). Thyroid-stimulating hormone, total and free thyroxine (T4) and triiodothyronine (T3) were determined and compared between ICU outcome groups. Results: We included twenty-nine patients. TSH levels were comparable in non-survivors (n = 17) and survivors (n = 12). The free T4 levels were higher in non–survivors than in survivors (P = 0.001), whereas the free T3 levels were comparable. All samples’ results similarly declined in both outcome groups up to 72 h after start of 24 h hypothermia. ROC curves analyses showed a maximum AUC of 0.83 (P = 0.003) for free T4 at the end of hypothermia with an optimal cut off ≥17.8 pmol/L to obtain 100 % specificity and positive predictive value for non-survival. Conclusion: Non-survival after cardiac arrest, coma, and therapeutic hypothermia following successful resuscitation is associated with a transient increase in free T4, most probably due to inhibition of free T4 to T3 conversion. However, before routine clinical application, external validation of our finding to assess generalizability is warranted.

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