Thyroid hormone responses in hemorrhagic shock: study in dogs and preliminary findings in humans.

One hour of hemorrhagic shock in the dog produces alterations in thyroid hormone metabolism far exceeding those seen after elective surgery or thermal injury. The changes in plasma thyroid hormone levels cannot be fully explained by carrier protein loss. Plasma concentrations of total thyroxine (T4) and triiodothyronine (T3) were significantly decreased after only 20 minutes of shock, continued to decrease throughout shock and resuscitation, and remained depressed for several days thereafter. Both hormones reached nadirs during volume replacement of 42% and 17% of baseline, respectively. The total T4 level normalized by the fifth postshock day, but the T3 concentration was still depressed on the ninth day. Plasma albumin, the principal canine thyroid hormone carrier, was significantly reduced 20 minutes after hemorrhage and remained low throughout convalescence. Concentrations of free T4 and T3 decreased during shock, but not as much as the total T4 and T3 concentrations. Reverse T3 levels, corrected for albumin loss, and T3 uptake values were increased during shock and resuscitation. Similar alterations in circulating thyroid hormone concentrations were seen in three patients with major traumatic injury and/or shock. The thyroid hormone changes in shock may represent another example of the "euthyroid sick syndrome."