EFFECT OF PULSATILE FLOW DURING CARDIOPULMONARY BYPASS ON THYROID-HORMONE METABOLISM

Changes in thyroid hormone levels during and after cardiopulmonary byp ass (CPB) are well documented. However, little is known about the effe cts of pulsatile flow during CPB on thyroid hormone metabolism. To exa mine the effect of flow pattern, a prospective study was carried out u sing 30 patients undergoing coronary artery bypass grafting. Fifteen p atients had pulsatile flow during CPB and 15, nonpulsatile flow. Serum samples were obtained preoperatively, during bypass, and at 2 and 24 hours postoperatively. Thyroid-stimulating hormone, thyroxine (T-4), t riiodothyronine (T-3), free T-4, and free T-3 levels were measured by radioimmunoassay. All measured hormone levels except free T-4 and thyr oid-stimulating hormone decreased after the initiation of CPB. There w ere no differences in preoperative values between the two groups. Howe ver, levels of T-3 and free T-3 during and after CPB showed a signific ant difference between the two groups, with a smaller decrease in pati ents in whom pulsatile flow was used during bypass (p < 0.05). Thyroxi ne, and thyroid-stimulating hormone free T-4 values showed no differen ce between the two groups at any sampling time. These data provide sup port for the use of pulsatile now during CPB to establish a more physi ologic state and maintain better thyroid hormone metabolism.