The background of the study. Patients with nonthyroidal illness, particularly those in intensive-care units, may have low serum thyrotropin (TSH) concentrations, which may be caused by drugs given to increase cardiac output. The effects of three such drugs, dopamine, dobutamine, and dopexamine, on TSH secretion were evaluated in this study.
How the study was done. The study subjects were 30 men who underwent elective major abdominal surgery. One day after surgery, the men were randomly assigned to receive dopamine, dobutamine, or dopexamine for eight hours. The dose was increased gradually at 10-minute intervals as needed to raise cardiac output by 35 percent, and then maintained at this level. Cardiac output, oxygen delivery, oxygen consumption, and serum TSH were measured at baseline and repeatedly during the infusions, and 2 and 16 hours later.
The results of the study. During the infusions, cardiac output increased by 36 to 38 percent, oxygen delivery by 31 to 34 percent, and oxygen consumption by 22 to 23 percent in the three groups. The average final infusion rates were 5.0 µg/kg/min for dopamine, 4.1 µg/kg/min for dobutamine, and 0.7 µg/kg/min for dopexamine.
In the men given dopamine, the average serum TSH concentration decreased from 1.1 mU/L to 0.3 mU/L in two hours. The mean values were <0.3 mU/L during the rest of the infusion, and they were similar to base line 2 and 16 hours after the infusion. There were no changes in serum TSH concentrations in the men given dobutamine or dopexamine.
The conclusions of the study. In postoperative surgical patients, infusions of dobutamine and dopexamine have little effect on TSH secretion, whereas a dose of dopamine that has a similar cardiac effect inhibits TSH secretion.
The original article. Schilling T, Grundling M, Strang CM, Moritz KU, Siegmund W, Hachenberg T. Effects of dopexamine, dobutamine or dopamine on prolactin and thyreotropin serum concentrations in high-risk surgical patients. Intensive Care Med 2004;30:1127-33.