Influence of extradural blockade on serum thyroid hormone concentrations after surgery

To study the changes in thyroid hormone metabolism after surgery, the influence of neurogenic blockade by extradural local anaesthetics, and possible hormonal interactions, 16 women undergoing cholecystectomy were randomly allocated to two groups of eight each. All patients received general anaesthesia and in addition one group received extradural blockade for 24 h. Preoperatively and at 2, 4, 6, 12 and 24 h after skin incision arterial serum concentrations of thyroid hormones (T3, free T3, rT3, T4, free T4 and TSH), catecholamines (adrenaline and noradrenaline), cortisol and serum proteins (albumin, prealbumin and TBG) were determined. In both groups total T3, free T3, total T4 and TSH decreased significantly whereas free T4 was unchanged and rT3 increased. No differences between the extradural group and the controls regarding thyroid hormones were observed, in spite of suppressed catecholamine and cortisol concentrations in the extradural group as compared to the control group. All serum thyroid hormone binding proteins decreased significantly in both groups. Changes in thyroid hormone metabolism after surgery seem independent of neurogenic blockade by extradural local anaesthetics, and of plasma catecholamine and cortisol concentrations.