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Reversing the fall in serum triiodothyronine during cardiac surgery does not alter the hemodynamic and metabolic responses to the surgery
The background of the study. The most common abnormality of thyroid function in patients with nonthyroidal illness is a transient fall in serum triiodothyronine (T3) concentrations. This fall may be a beneficial adaptation to illness. In this study, the effect of T3 replacement on cardiovascular function and protein metabolism was studied in patients undergoing coronary-artery surgery.
How the study was done. The study subjects were 59 patients with coronary artery disease who underwent elective coronary-artery bypass grafting. They were randomly assigned to receive T3, given intravenously, or placebo, for 24 hours after surgery. Serum T3, thyrotropin (TSH), cardiac output, vascular resistance, oxygen saturation, heart rate, and protein metabolism were measured periodically for up to 36 hours after surgery.
The results of the study. The average serum T3 concentration fell from 150 to 50 ng/dl at the end of surgery in both groups. Thereafter, it increased to 140 to 16 ng/dl during the 24-hour infusion. In contrast, the serum T3 concentrations were 50 ng/dl throughout the 24-hour infusion in the placebo group.
Postoperatively, there were no consistent differences in cardiac output, vascular resistance, or oxygen saturation in the two groups, and there were similar increases in heart rate in each group (22 beats/minute in the T3 group and 19 beats/minute in the placebo group). There were no differences in the frequency of cardiac rhythm abnormalities or the need for cardiac drugs in the two groups, and there were no episodes of cardiac ischemia in either group.
Urinary nitrogen excretion and amino acid metabolism increased slightly after surgery, and the increases were similar in the two groups.
The conclusions of the study. Serum T3 concentrations fall substantially during elective cardiac surgery and remain low for at least 36 hours after surgery. Maintaining normal serum T3 concentrations after surgery does not alter cardiovascular function or protein metabolism during the immediate postoperative period.
The original article. Spratt DI, Frohnauer M, Cyr-Alves H, Kramer RS, Lucas FL, Morton JR, Cox DF, Becker K, Devlin JT. Physiological effects of nonthyroidal illness syndrome in patients after cardiac surgery. Am J Physiol Endocrinol Metab 2007;293:E310-E315.
| Thyroid Digest Index | | | November 2007 Thyroid Digest |
