Prostaglandin F1 alpha levels during and after neonatal extracorporeal membrane oxygenation. Infants receiving extracorporeal membrane oxygenation therapy undergo long-term cardiopulmonary bypass, are systemically heparinized, and frequently receive platelet transfusions. Prostacyclin is a powerful inhibitor of platelet aggregation as well as a potent vasodilator. The levels of its stable metabolite prostaglandin F1 alpha increase significantly in children undergoing cardiopulmonary bypass during heart operations but decrease to preoperative levels after bypass. To determine the effect of long-term bypass on prostacyclin levels, multiple plasma samples were analyzed in 10 human neonates both during extracorporeal membrane oxygenation therapy and within 24 hours after extracorporeal membrane oxygenation. Prostaglandin F1 alpha, the stable metabolite of prostacyclin, was quantitated by radioimmunoassay in picograms per milliliter. Prostaglandin F1 alpha levels were elevated while the patients received extracorporeal membrane oxygenation therapy but decreased with duration of extracorporeal membrane oxygenation. In most infants, prostaglandin F1 alpha levels rose again during weaning from extracorporeal membrane oxygenation and remained elevated for 24 hours after extracorporeal membrane oxygenation. Extracorporeal membrane oxygenation course influenced circulating prostaglandin F1 alpha levels. Fluctuating prostaglandin F1 alpha levels are of clinical significance in the management of vasomotor tone and platelet function, common problems in the care and the prevention of hemorrhage in these critically ill infants. 