An inflammatory response and a capillary leak syndrome frequently develop during the treatment of neonatal respiratory failure by extracorporeal membrane oxygenation (ECMO). The present study was performed to investigate leukocyte activation and endothelial cell dysfunction that are associated with prolonged contact of blood components with synthetic surfaces. Laboratory ECMO was performed with fresh human blood at 37°C for 8 h (n ϭ 6). Leukocyte activation was measured by L-selectin (CD62L) and CD18 integrin surface expression and by neutrophil-derived elastase release. To monitor endothelial activation, endothelial cell ICAM-1 (CD54) expression was measured in cultured endothelial cells from human umbilical veins (HUVEC) after incubation with plasma from the ECMO experiments. CD18 integrin expression was found significantly upregulated on polymorphonuclear neutrophils and monocytes after 2-4 h of laboratory ECMO. L-selectin was reduced on both cell types during the total duration of the experiments. Soluble L-selectin (sCD62L) and total and differential leukocyte counts remained unchanged during the experiment. Neutrophil-derived elastase content was maximal after 8 h of ECMO. Plasma from the ECMO experiments did not induce ICAM-1 expression of cultured HUVEC. We conclude that prolonged contact with synthetic surfaces during ECMO activates phagocytes, which may contribute to the inflammatory response seen in ECMOtreated patients. Activated phagocytes do not accumulate in the extracorporeal system nor release humoral factors inducing ICAM-1 expression on endothelial cells. ECMO is the standard treatment for newborn infants with respiratory failure unresponsive to conventional pulmonary support (1). During ECMO treatment, an inflammatory reaction with neutropenia (2), activation of PMN (3), and a capillary leak syndrome with systemic and pulmonary edema (4, 5) have been described. However, it is not clear, to what extent this changes result from the patient's disease (6) or from the effects of extracorporeal circulation of the blood. We therefore performed laboratory ECMO without connecting the system to a patient, to study the isolated effects of prolonged extracorporeal circulation of blood on leukocyte number, expression of leukocyte adhesion molecules, and the release of mediators that might activate endothelial cells.During hemodialysis or cardiopulmonary bypass (CPB), leukocytes are activated (2, 7, 8) and humoral mediators are generated, which impairs endothelial cell integrity (9 -11). The induction of an inflammatory response and the loss of endothelial integrity represent a hallmark of the capillary leakage commonly observed in CPB (7) and neonatal ECMO (4, 5), with systemic and pulmonary edema often prolonging the duration of ECMO. In spite of evidence for activation of PMN in neonatal ECMO (3), it is unclear to what extent this activation is due to the underlying disease or the leukocyte-synthetic surface interaction and whether this activation is linked to the clinically observed changes in endothel...

The leukocyte glycoprotein L-selectin mediates an early step in the recruitment of leukocytes to sites of inflammation. L-Selectin surface expression is rapidly down-regulated by inflammatory signals in vitro. In a prospective study, we found L-selectin expression on umbilical cord blood granulocytes and monocytes to be significantly decreased in newborn infants with acute bacterial infection compared with controls (p < 0.01). A significantly reduced L-selectin expression of both granulocytes and monocytes was also found to be associated with an increased neutrophil immature/total ratio (p < 0.01) but not with other laboratory markers of neonatal sepsis. There was no apparent impact of prematurity, low birth weight, gestational hypertension, or gestational diabetes on L-selectin expression. Although the mode of delivery did not affect granulocyte L-selectin expression, umbilical cord blood monocytes showed an increased L-selectin expression after emergency cesarean delivery compared with samples obtained after elective cesarean or vaginal delivery (p < 0.01). We conclude that acute systemic inflammation results in down-regulation of granulocyte and monocyte L-selectin expression in vivo similar to that observed in vitro.

Complment activation during extracorporeal membrane oxygenation (ECMO) in newborns can be caused by both the underlying disease processes and by blood contact with the ECMO circuit. We investigated the relative importance of these mechanisms by measuring C3a, C5a and sC5b-9 before, during and after neonatal ECMO in six consecutive newborn patients using enzyme-linked immunoassay. In addition complement activation during in vitro ECMO with repeated flow of the same blood volume was measured using blood from healthy adult donors. C3a increased significantly in vivo after 1 h (from 1035+/-193 to 1865+/-419 microg/l) and in vitro ECMO (from 314+/-75 to 1962+/-1062 microg/l). C5a increased during ECMO without significant differences between in vivo and in vitro activation. In neonatal patients, sC5b-9 rose faster than in vitro, but the rapid increase was also significant for in vitro experiments (in vivo: from 328+/-63 to 1623+/-387 microg/l after 2 h; and in vitro: from 78+/-32 to 453+/-179 microg/l after 8 h). After this initial peak at 1-2 h, complement activation decreased gradually until 2-3 days after the initiation of ECMO. We conclude that in newborns the rapid activation of the complement system after the start of ECMO is predominantly caused by contact with artificial surfaces rather than the patient's underlying disease.

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