Objectives: Recent studies have shown that an injury occurs when the hypoxic heart is suddenly reoxygenated (as occurs with cardiopulmonary bypass), resulting in myocardial depression, impaired oxygenation, and increased pulmonary vascular resistance, We hypothesize that this injury is, in part, due to oxygen-derived radicals produced by activated white cells and may therefore be ameliorated by limiting leukocytes in the bypass circuit, Methods: Fifteen neonatal piglets underwent 60 minutes of ventilator hypoxia (inspired oxygen fraction 8% to 10%), followed by reoxygenation with cardiopulmonary bypass at an inspired oxygen fraction of 100% for 90 minutes, In nine piglets (group I) our routine bypass circuit was used with no modifications, and in six piglets (group 2) a leukocyte-depleting filter (Pall BC-1; Pall Biomedical Products Corporation, Glencoe, N,Y,) was inserted in the arterial line to lower the neutrophil count, Six additional piglets underwent 90 minutes of bypass without hypoxia (cardiopulmonary bypass controls), Postbypass myocardial and pulmonary function was assessed by pressure volume loops, arterial/alveolar ratio, and pulmonary vascular resistance index, Results are expressed as a percentage of control, Results: By comparison with group 1 piglets (reoxygenation, without a filter), hypoxic piglets undergoing reoxygenation with a leukocyte-depleting filter (group 2) had improved myocardial systolic function (88% vs 52%; p < 0.05), diastolic compliance (175% vs 275%; p < 0.05), and preload recruitable stroke work (91% vs 54%; p < 0.05); had better preservation of the arterial/alveolar ratio (97% vs 74%; p < 0.05); and had less increase in pulmonary vascular resistance (229% vs 391%; p < 0.05), Furthermore, leukocyte filtration prevented adenosine triphosphate depletion or a change in tissue antioxidants, Conversely, unprotected piglets (group 1) exhibited lower levels of adenosine triphosphate and significant loss of tissue antioxidants. Indeed, the results in the leukocyte-filtered piglets (group 2) were nearly identical to those of piglets subjected to bypass without hypoxia (controls), Conclusions: (1) This study demonstrates that a major component of the injury that occurs when the hypoxic heart is abruptly reoxygenated is caused by oxygen radicals produced by white blood cells; (2) this injury can be prevented by a leukocyte-depleting filter; and (3) avoidance of this injury improves postbypass myocardial and pulmonary function, These data suggest that leukocyte depletion should be used routinely in all children undergoing operations for cyanotic heart disease or extracorporeal membrane oxygenation.
