SYNERGISM BETWEEN ATRACURIUM AND VECURONIUM IN INFANTS AND CHILDREN DURING NITROUS OXIDE-OXYGEN-ALFENTANIL ANESTHESIA

This study was undertaken to see if infants are more sensitive than ch ildren to a combination of atracurium and vecuronium in an equipotent dose ratio:(mu g:mu g) 5:1 in infants and 4:1 in children. We studied 15 infants (1-11 months old) and 15 children (3-10 yr old) during nitr ous oxide-oxygen-alfentanil anaesthesia. Neuromuscular function was re corded by adductor pollicis EMG. An individual dose-response curve of the atracurium-vecuronium combination was determined for every patient and its potency compared with that of the parent agents alone. The co mbination was significantly more potent than one parent agent, both in infants (P < 0.01) and in children (P < 0.0001). However, infants wer e less sensitive than children to synergism produced by the atracurium -vecuronium combination: if the ED(50) dose of the parent agent is def ined as one dose equivalent, then the mean ED(50) doses of the combina tion were 0.81 (SEM 0.05) and 0.64 (0.03) dose equivalents in infants and children, respectively (P < 0.01). We suggest that an interaction between two binding sites of competitive neuromuscular blocking agents in postsynaptic acetylcholine receptors may explain both the synergis m and sensitivity of infants to non-depolarizing neuromuscular blockin g agents.