MIVACURIUM IN THE MYASTHENIC PATIENT

We have used mivacurium in four myasthenic patients presenting for thy mectomy. Supramaximal single twitch stimulation was applied to the uln ar nerve at the wrist and the force of contraction of the adductor pol licis was measured. After an initial bolus dose of 30 mu g kg(-1) (app roximately one-fifth of the normal intubating dose), we observed a mea n 37.5 (SEM 5.6) % reduction in evoked twitch tension, Neuromuscular b lock was increased with incremental doses and maintained with repeat b olus doses of 15 mu g kg(-1) at 25% recovery. The interval between mai ntenance bolus doses remained constant (mean 5.9 (0.7) min). Spontaneo us offset was rapid with a mean recovery index (T25-T75) of 11.9 (2.1) min. Provided anticholinesterase therapy is withheld in the immediate preoperative period, mivacurium would appear to be a safe and appropr iate neuromuscular blocker in this variably sensitive group of patient s. The cumulative dose required to establish full neuromuscular block varied between 60 and 90 mu g kg(-1). A maintenance infusion, commenci ng at 3 mu g kg(-1) min(-1), is recommended, guided by neuromuscular m onitoring.