THE EFFECT OF EPIDURAL BUPIVACAINE ON VECURONIUM-INDUCED NEUROMUSCULAR BLOCKADE IN CHILDREN

The effect of epidural bupivacaine on potency and duration of action of vecuronium-induced neuromuscular blockade (NMB) was evaluated in 30 general surgical paediatric patients (ASA I-II) of three to ten years of age. Premedication was midazolam 0.5 mg kg(-1) orally (max 15 mg). In addition to general anaesthesia, 15 of the children received a lumbar epidural block with 0.5% bupivacaine 2.5 mg kg(-1). Anaesthesia was induced and maintained with N2O:o(2) (2:1), propofol and alfentanil. NMB was monitored by adductor pollicis EMG with the train-of-four stimulus every 20 sec. Thirty minutes following the epidural bupivacaine injection (mean plasma concentration 0.86 mu g ml(-1)) or induction of anaesthesia a cumulative dose-response curve of vecuronium was established to achieve a 95% depression of the twitch response. Thereafter, NMB was allowed to recover spontaneously. ED doses of vecuronium were 19-22% greater in the control group than in the epidural group. ED(50) doses were 33.8 (s.e.mean 1.3) mu g kg(-1) and 28.4 (2.2) mu g kg(-1); respectively (P< 0.05). There were no differences in recovery times from NMB between control and epidural group, the recovery index (time of twitch height to recover from 25 to 75%) being 6.4 (0.4) min and 7.0 (0.9) min, respectively. However, a negative correlation was found between bupivacaine plasma concentration and an ED(50) dose of vecuronium (P=0.01). Our results indicate that vecuronium is slightly more potent in children with bupivacaine epidural block than in children without it.