Influence of age on the dose-response relationship of atracurium in paediatric patients.

To assess the influence of age on the dose-response relationship of atracurium in paediatric patients during thiopental-fentanyl-N2O-O2-anaesthesia, we studied 85 patients from neonates to adolescents. Each patient was given two doses of atracurium: following the maximum EMG response to the first dose of 150 micrograms/kg, an individual second dose was given, to produce exactly 95% neuromuscular block. The onset time of atracurium (time from administration to maximum effect) was shortest in neonates (2.6 min) and infants (3.3 min) and longest in adolescents (5.5 min) (P less than 0.01). The dose-response curves were parallel in all patients aged 3 months or older. The ED95 of atracurium was comparable for neonates and infants (226 micrograms/kg). This was 28% less than the ED95 for patients aged 1 year or older (316 micrograms/kg) (P less than 0.01). The results explain the slightly longer-lasting neuromuscular block in infants as compared to children following a constant atracurium dose in micrograms/kg. The great individual variability of the neuromuscular response, however, indicates that neuromuscular monitoring is essential in paediatric patients.