Objective: To investigate the relationship and possible role of soluble adhesion molecule E-selectin in the postoperative course in children undergoing cardiopulmonary bypass (CPB). Design: Prospective cohort study. Setting:Pediatric intensive care unit of a university hospital. Participants: Thirteen children who were candidates for cardiac surgery. Interventions: None. Measurements and Main Results: Serial blood samples of 13 CPB patients were collected from the arterial catheter or from the bypass circuits preoperatively; on initiation of CPB; on termination of CPB; and 1, 2, 4, 8,12, 18, 24, and 48 hours postoperatively. Plasma was recovered immediately, aliquoted, and frozen at -70 degrees C until use. Circulating soluble selectin molecules were measured with a sandwich enzyme-linked immunosorbent assay technique. There were significant changes in plasma levels of soluble E-selectins in patients after CPB, and these levels were associated with patient characteristics, operative variables, and postoperative course. Soluble E-selectin correlated significantly with inotropic support and the use of anti-inflammatory drugs. There was a significant association between the development of postoperative sepsis and soluble E-selectin levels. No correlation was found between soluble E-selectins and duration of CPB, aortic cross-clamping, or hemodynamic variables, including heart rate and mean systemic arterial pressure. Conclusion: These results suggest a relationship between CPB-induced mediators and early and late clinical effects. Although the mechanism for the increase of soluble E-selectin remains to be elucidated, the upregulation of soluble E-selectin indicates neutrophil activation, and its inhibition may represent a target for reducing the inflammatory response associated with CPB. Copyright (C) 2000 by W.B. Saunders Company.