Recovery characteristics after early administration of anticholinesterases during intense mivacurium-induced neuromuscular block
The time course of recovery after early administration of anticholinesterases during intense mivacurium-induced block was evaluated by recording the mechanomyographic response of the adductor pollicis to post-tetanic count (PTC) and train-of-four (TOF) ulnar nerve stimulation. Seventy-two adult patients receiving thiopentone, fentanyl, nitrous oxide, isoflurane anaesthesia and mivacurium 0.15 mg kg-1 were allocated randomly to one of six equal groups according to the type of anticholinesterase and intensity of block at which antagonism was attempted. Groups 1, 3 and 5 received neostigmine 0.07 mg kg-1, while groups 2, 4 and 6 received edrophonium 1 mg kg-1. At the time of administration of antagonist there was no response to PTC in groups 1 and 2, a PTC of 1 or more was detectable in groups 3 and 4 and the first twitch of the TOF (T1) had recovered to 10% in the conventional antagonism groups (5 and 6). The longest clinical duration (CD) values (time from administration of mivacurium to T1 25%) were encountered 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 significantly in 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 (RI) (time interval 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 groups 1-6, respectively and was prolonged with neostigmine antagonism at PTC 0 (group 1). Reversal time (RT) (time between administration of antagonist and TOF 0.70) was 34.9 (16.6) min in group 1 who received neostigmine at PTC 0 and was prolonged markedly compared with all other groups. Antagonism with edrophonium at PTC 0 (group 2) was associated with an RT of 16.7 (5.1) min and was significantly longer compared with the conventional antagonism groups only. Reversal times were similar in groups 3-6. Total recovery times (TRT) (time between administration of mivacurium and 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, administration of neostigmine during intense mivacurium block, not responsive to TOF and PTC stimulation was associated with marked delay in recovery, possibly because of inhibition of plasma cholinesterase. At this intensity of block, edrophonium was preferable. It is advisable to wait for a detectable PTC before attempting antagonism of an intense mivacurium block. After detection of PTC, neostigmine or edrophonium antagonism reduced the clinical duration but not the total recovery time compared with conventional reversal administered at T1 10%.