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 T-3 (fT(3)), reverse T-3 (rT(3)), 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 degrees 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 T-3 was reduced for up to 3 days after CPB (p<0.05), mean serum rT(3) 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.