DETRIMENTAL EFFECTS OF CARDIOPULMONARY BYPASS IN CYANOTIC INFANTS - PREVENTING THE REOXYGENATION INJURY

Background. Recent experimental studies have shown that acute hypoxia followed by abrupt reoxygenation using cardiopulmonary bypass (CPB) re sults in an unintended injury mediated by oxygen free radicals, which can be modified by initiating CPB at a lower fraction of inspired oxyg en (FiO(2)) or by leukocyte filtration. However, the clinical relevanc e of these experimental studies has been questioned because chronic hy poxia may allow compensatory changes to occur. Methods. Seven acyanoti c infants had CPB initiated at an FiO(2) of 1.0. Of 21 cyanotic infant s, 7 (group 1) had CPB initiated at an FiO(2) of 1.0, 6 (group 2) at a n FiO(2) of 0.21, and 8 (group 3) underwent CPB using leukocyte filtra tion. Biopsy of right atrial tissue was performed before and 10 to 20 minutes after the initiation of CPB. The tissue was incubated in 4-mmo l/L t-butylhydroperoxide (a strong oxidant), and the malondialdehyde ( MDA) Bevel was measured to determine the antioxidant reserve capacity. The more MDA produced, the greater was the depletion of tissue antiox idants secondary to oxygen free radical formation during reoxygenation . Results. There was no difference in the prebypass antioxidant reserv e capacity between cyanotic and acyanotic hearts (492 +/- 72 versus 43 9 +/- 44 nmol MDA/g protein). However, after the initiation of CPB wit hout leukocyte filtration, MDA production rose markedly in the cyanoti c (groups 1 and 2) as compared with the acyanotic hearts (322% versus 40%; p < 0.05), indicating a depletion of antioxidants. In cyanotic he arts, initiating CPB at an FiO(2) of 1.0 (group 1) resulted in increas ed MDA production (407% versus 227%) as compared with hearts in which CPB was initiated at an FiO(2) of 0.21 (group 2), indicating a greater generation of oxygen free radicals in group 1. Conversely, there was only a minimal increase in MDA production in 8 of the 21 infants (grou p 3) in whom white blood cells were effectively filtered (19% versus 3 22%; p < 0.05). Conclusions. First, increased amounts of oxygen free r adicals are generated in cyanotic infants with the initiation of CPB. Second, this production is reduced by initiating CPB at an FiO(2) of 0 .21 or by effectively filtering white blood cells. Third, these change s parallel those seen in the acute experimental model, validating its use for future study. (C) 1997 by The Society of Thoracic Surgeons.