Plasma concentrations of bupivacaine after combined spinal epidural anaesthesia in infants and neonates.

The unbound and bound plasma concentration of bupivacaine in 50 infants less than 55 weeks postconceptual age was determined following combined spinal and epidural anaesthesia (csea). Plasma concentrations were determined at 15-min intervals up to 60 min postspinal anaesthesia. Maximum plasma bupivacaine levels were recorded between 45 and 60 min post CseA. Total plasma concentrations above a toxic threshold level of 4 microg.ml(-1) were recorded in 4% of patients and above 2.5 microg.ml(-1) in 10% of patients. Unbound bupivacaine levels were greater than a presumed toxic level of 0.25 microg.ml(-1) in 16% of cases and above 0.3 microg. ml(-1) in 14% of cases. A wide range of protein binding was measured (varying from 53.8-98.2%) and could not be correlated with standard indicators of local anaesthetic binding. Two neonates had brief apnoeas in the immediate perioperative phase but no adverse cardiac or central nervous system events attributable to the performance of Csea were demonstrated.