Cardiopulmonary bypass temperature does not affect postoperative euthyroid sick syndrome?

STUDY OBJECTIVE

To determine if temperature during cardiopulmonary bypass (CPB) has an effect on perioperative and postoperative thyroid function.

DESIGN

Prospective study comparing thyroid function during and after hypothermic and normothermic CPB.

SETTING

Cardiac surgical unit at a university-affiliated hospital.

PATIENTS

Twelve patients scheduled to undergo cardiac operations with normothermic (n = 6) or hypothermic (n = 6) CPB.

INTERVENTIONS

Blood was analyzed for serum concentration of total thyroxine (TT4), total triiodothyronine (TT3), free T3 (fT3), reverse T3 (rT3), and thyroid stimulating hormone (TSH) preoperatively, 60 min after CPB was initiated, 30 min after discontinuing CPB, and on postoperative days (POD) 1, 3, and 5.

MEASUREMENTS AND RESULTS

Patients who underwent either cold (26 degrees +/- 5 degrees C) or warm (35 degrees +/- 1 degree C) CPB were comparable with regard to age, body weight, duration of CPB, cross-clamp time, use of inotropes, total heparin dose, and length of hospital stay. Incidence of postoperative myocardial infarction, congestive heart failure, and death were similar. In both groups, TT4 and TT3 were reduced below baseline values beginning with CPB and persisting for up to 5 days after CPB (p < 0.05), free T3 was reduced for up to 3 days after CPB (p < 0.05), mean serum rT3 was elevated on POD 1 and POD 3 (p < 0.05), and TSH remained unchanged.

CONCLUSION

The results of this study suggest that normothermic CPB does not prevent the development of the "euthyroid sick syndrome" during and after CPB. Despite these changes in thyroid function, most patients in both groups had a normal postoperative recovery.