TIME-COURSE OF FREE-RADICAL ACTIVITY DURING CORONARY-ARTERY OPERATIONS WITH CARDIOPULMONARY BYPASS

Myocardial and pulmonary impairment after cardiopulmonary bypass may b e caused by oxygen free radicals produced by reperfusion and by activa ted neutrophils. Free radical activity was assessed by assays for lipi d peroxidation (thiobarbituric acid-reactive material) and phospholipi d-esterified diene conjugation (18:2[9,11]/18:2[9,12] molar ratio) in 25 patients during coronary artery operations. Arterial blood samples were obtained before, during the ischemic period, and for 24 hours the reafter. There were no significant changes in free radical indices dur ing the ischemic periods, but after cessation of bypass they increased significantly. Ten minutes after bypass thiobarbituric acid-reactive material rose from 96 (median; range 65 to 145) nmol/gm albumin to 138 (85 to 200) nmol/gm albumin (p < 0.001), and molar ratio rose from 2. 23% (0.45% to 7.70%) to 2.51% (0.39% to 7.93%) (p < 0.02). Values of t hiobarbituric acid-reactive material subsequently decreased, but molar ratio reached a peak at 4 hours after bypass, 2.64% (0.55% to 10.08%) (p < 0.001), thereafter returning to baseline. The postoperative incr eases in thiobarbituric acid-reactive material and in molar ratio were correlated (r = +0.53; p = 0.006). These increases in thiobarbituric acid-reactive material and in molar ratio were not related to age, pre operative left ventricular function, or the number of grafts performed . Increase in thiobarbituric acid-reactive material correlated with th e duration of cardiopulmonary bypass (r = +0.43; p = 0.03). In 10 pati ents in whom cardiopulmonary bypass was performed using a bubble oxyge nator, the increases in thiobarbituric acid-reactive material were sig nificantly greater than in the 15 in whom a membrane oxygenator was us ed (p < 0.02). These data show that after apparently uncomplicated cor onary operations with bypass there is an increase in lipid peroxidatio n and diene conjugation, indicating increased free radical activity. T his increase varies between patients and does not relate to patient or surgical factors but may depend on the type of oxygenator employed du ring bypass.