Recovery characteristics after early administration of anticholinesterases during intense mivacurium-induced neuromuscular block

The time course of recovery after early administration of anticholinesterasesduring intense mivacurium-induced block was evaluated by recordingthe mechanomyographic response of the adductor pollicis to post-tetaniccount (PTC) and train-of-four (TOF) ulnar nerve stimulation.Seventy-two adult patients receiving thiopentone, fentanyl,nitrous oxide, isoflurane anaesthesia and mivacurium 0.15 mgkg^–1 were allocated randomly to one of six equal groupsaccording to the type of anticholinesterase and intensity ofblock at which antagonism was attempted. Groups 1, 3 and 5 receivedneostigmine 0.07 mg kg^–1, while groups 2, 4 and 6 receivededrophonium 1 mg kg^–1. At the time of administration ofantagonist there was no response to PTC in groups 1 and 2, aPTC of 1 or more was detectable in groups 3 and 4 and the firsttwitch of the TOF (T1) had recovered to 10% in the conventionalantagonism groups (5 and 6). The longest clinical duration (CD)values (time from administration of mivacurium to T1 25%) wereencountered in groups 1, 5 and 6 and were 17.4 (7.9), 19.7 (3.4)and 21.4 (4.8) min, respectively. CD was reduced significantlyin groups 2, 3 and 4 and values were 13.9 (3.5), 13.7 (3.5)and 13.8 (3.3) min, respectively. Recovery indices (Rl) (timeinterval between T1 25% and 75%) were 13.8 (7.3), 6.3 (1.4),4.6 (1.8), 6.0 (2.1), 3.7 (2.2) and 4.8 (3.1) min in groups1–6, respectively and was prolonged with neostigmine antagonismat PTC 0 (group 1). Reversal time (RT) (time between administrationof antagonist and TOF 0.70) was 34.9 (16.6) min in group 1 whoreceived neostigmine at PTC 0 and was prolonged markedly comparedwith all other groups. Antagonism with edrophonium at PTC 0(group 2) was associated with an RT of 16.7 (5.1) min and wassignificantly longer compared with the conventional antagonismgroups only. Reversal times were similar in groups 3–6.Total recovery times (TRT) (time between administration of mivacuriumand TOF 0.70) were 41.5 (16.6), 23.2 (5.2), 23.2 (5.3), 24.1(4.5), 26.8 (4.8) and 28.5 (9.1) min in groups 1–6, respectively,and was markedly prolonged in group 1 only. In summary, administrationof neostigmine during intense mivacurium block, not responsiveto TOF and PTC stimulation was associated with marked delayin recovery, possibly because of inhibition of plasma cholinesterase.At this intensity of block, edrophonium was preferable. It isadvisable to wait for a detectable PTC before attempting antagonismof an intense mivacurium block. After detection of PTC, neostigmineor edrophonium antagonism reduced the clinical duration butnot the total recovery time compared with conventional reversaladministered at T1 10%.