PLASMA FENTANYL LEVELS IN INFANTS UNDERGOING EXTRACORPOREAL MEMBRANE-OXYGENATION

Plasma levels of fentanyl were analyzed in 12 infants undergoing extra corporeal membrane oxygenation who received a fentanyl bolus (5 to 10 mug/kg) followed by infusion at 1 to 6.3 mug/kg/hr. Fentanyl levels, a veraging 11 samples/infant, were measured by radioimmunoassay (mean 19 .7 +/- 35.7 ng/ml; n = 140). Eight of the infants, all with a primary diagnosis other than congenital diaphragmatic hernia, survived with re latively short (<7 days) courses on extracorporeal membrane oxygenatio n; this group of infants did not develop tolerance to fentanyl and cou ld be maintained on infusion rates of <5 mug/kg/hr throughout. The fou r infants with congenital diaphragmatic hernia had longer extracorpore al membrane oxygenation runs and three did not survive; their plasma f entanyl levels were consistently higher and while the infusion rates w ere higher early on extracorporeal membrane oxygenation, they did not exceed 7 mug/kg/hr and actually decreased after 5 days on extracorpore al membrane oxygenation. Five infants (42%) received lorazepam in addi tion to fentanyl for at least one sampling time. The fentanyl infusion dose and plasma level were higher in the congenital diaphragmatic her nia nonsurvivors who did not receive lorazepam (p < 0.001). A decrease in fentanyl clearance correlated with renal dysfunction (p < 0.01). A bolus of fentanyl followed by infusion of relatively low doses (1 to 5 mug/kg/hr) provides adequate analgesia for infants on extracorporeal membrane oxygenation, particularly when it is supplemented with intra venous lorazepam whenever needed to control infant movement.