NEUROMUSCULAR AND HEMODYNAMIC-EFFECTS OF MIVACURIUM IN ELDERLY AND YOUNG-ADULT PATIENTS

We have studied the neuromuscular effects of mivacurium and changes in heart rate and arterial pressure in 40 elderly (aged 70 yr) and 20 yo ung adult (aged 18-40 yr) patients anaesthetized with thiopentone, fen tanyl, nitrous oxide in oxygen and halothane. Neuromuscular block was monitored by train-of-four (TOF) stimulation of the ulnar nerve and re cording of the force of contraction of the adductor pollicis muscle us ing a force displacement transducer and a neuromuscular function analy ser (Myograph 2000, Biometer Ltd). Twenty elderly and 10 young adults received single doses of mivacurium 0.15 mg kg(-1) and spontaneous rec overy was recorded. The other 20 elderly and 10 adults received the sa me dose but an infusion was started at T1 (first response in TOF) of 1 0% and the block maintained at this level. Haemodynamic effects were s tudied after administration of mivacurium over 15 or 5 s in elderly (n = 10 each) and over 5 s in adult (n = 10) patients. Onset of maximum block occurred at a mean time of 122 (SD 32) and 125 (49) s in elderly and young adults, respectively. Recovery of T1 to 25% occurred in 22. 0 (5.7) and 17.2 (4.4) min, and T1 to 90% in 32.8 (6.9) and 24.4 (5.8) min in elderly and adult subjects, respectively. Recovery of the TOF ratio to 0.7 occurred in 32.8 (7.1) and 26.0 (15.0) min in the elderly and young subjects, respectively (all P(0.05 between young and elderl y). Mean mivacurium requirements by continuous infusion for maintenanc e of 90% block were 3.67 and 5.50 mu g kg(-1) min(-1) in elderly and t he young adults, respectively (P < 0.05). In the elderly, neuromuscula r effects were prolonged by approximately 30% and infusion requirement s reduced by 38%. Residual neuromuscular block was antagonized easily with edrophonium or neostigmine. Except for small changes in systolic arterial pressure, mivacurium exhibited good haemodynamic stability in both groups. Cutaneous flushing was observed in six elderly (15%) and six young adults (30%).