Platelet hyporeactivity in young infants during cardiopulmonary bypass

Platelet dysfunction is one of the most important factors contributing to a postoperative hemorrhagic diathesis in children with congenital heart disease undergoing operations requiring cardiopulmonary bypass (CPB). However, very little is known about the influence of CPB on platelets in neonates and young infants. We studied 16 patients--8 young infants (<2 mo old) and 8 children (>12 mo old)--with congenital heart disease undergoing CPB. Surface density of an important platelet adhesive receptor, glycoprotein Ib, and degree of platelet activation, indicated by p-selectin positivity, were measured by whole blood flow cytometry in samples obtained at seven time points during the operations. We found that the percentage of p-selectin-positive platelets increased significantly in children, but not in young infants, during CPB. The young infant group exhibited a significantly smaller reduction of glycoprotein Ib than the child group during CPB (21.0% +/- 12.0% vs 32.7% +/- 18.1%; P < 0.05). Lack of CPB-induced increase of p-selectin and a smaller decrease of glycoprotein Ib in young infants in the current study suggest reduced platelet reactivity in young infants and neonates during CPB. The clinical significance of the reduced platelet reactivity in young infants and neonates remains to be determined. Implications: Platelets of young infants are less reactive than those of children during cardiopulmonary bypass, as determined by the cardiopulmonary bypass-induced alterations in platelet membrane adhesive receptors.