Influence of antioxidants (mannitol and allopurinol) on oxygen free radical generation during and after cardiopulmonary bypass

Oxygen-derived free radicals (O₂^-, H₂O₂, OH·) are produced during oxidative metabolism, ischemia and reperfusion, and cardiopulmonary bypass (CPB). When oxygen free radical production exceeds scavening capacity, peroxidation of structural lipids in cell membranes can occur with potentially injurious consequences. In this prospective study, 45 patients were evaluated to determined the effect of CPB on oxygen free radical generation. Twenty patients in group I were controls. Exogenous oxygen free radical antioxidants were administered before bypass to patients in group II (n = 15, mannitol) and group III (n = 10, allopurinol). In group I, plasma H₂O₂ increased during extracorporeal circulation from 65 ± 6.0 to 125 ± 12 μM/ml (p < .001). At similar sampling intervals, plasma H₂O₂ levels were significantly lower in group II (p < .03) and group III (p < .05) when compared with those in group I. Red blood cell H₂O₂ did not change in group I or group II. White blood cell H₂O₂ levels decreased in group I (p < .04) and group II during CPB. (Intracellular concentrations of H₂O₂ were not obtained in group III patients). We conclude that cytotoxic oxygen radicals are generated during CPB and that pretreatment with free radical antioxidants, mannitol or allopurinol, may minimize the free radicals available for lipid peroxidation of biomembranes.