Low dose mivacurium is less effective than succinylcholine in electroconvulsive therapy

To compare the efficacy of low dose (LD) mivacurium (0.08 mg.kg-1) with LD succinylcholine (0.5 mg.kg-1) in modifying seizure activity during electroconvulsive therapy (ECT). Partial muscle relaxation is used in ECT to prevent violent muscle contractions. Current practice is to use LD succinylcholine which has several undesirable side effects. Sixteen depressed, but otherwise healthy, patients, aged 27-67 yr were studied. In a randomized, double-blind, cross-over study, either LD mivacurium or LD succinylcholine was given at consecutive ECTs 120 and 30 sec respectively before inducing ECT. Neuromuscular blockade following mivacurium was not reversed. Seizure modification was scored--0 = no seizure activity, 1 = over-modified, 2 = desired level, 3 = under-modified, 4 = unmodified. Duration of seizures, time to first breath and adequate ventilation, ability to protrude tongue and sustain hand grip for five seconds were recorded. Paired t-tests and Wilcoxon matched pairs test were used to compare data. P < 0.05 was considered significant. Seizure modification was better (mean (range)) after succinylcholine 2.06(1-3) than after mivacurium 2.56(2-4) (P < 0.05). Mivacurium was unsatisfactory in eight cases compared with two cases after succinylcholine. The study was terminated early because of unsatisfactory seizure control. Clinical assessments of recovery from both relaxants were similar. Low dose mivacurium is unsuitable for use in ECT.