OPTIMUM TIME FOR NEOSTIGMINE REVERSAL OF ATRACURIUM-INDUCED NEUROMUSCULAR BLOCKADE

Purpose: The aim of the study was to determine the optimum time for ad ministration of neostigmine during recovery from atracurium-induced ne uromuscular blockade. Methods: The study comprised 103 patients anaest hetised with midazolam, fentanyl, thiopentone, halothane, and nitrous oxide. Relaxation was induced with atracurium 0.5 mg . kg(-1) and main tained with supplements of 0.15 mg . kg(-1). The ulnar nerve was stimu lated with train-of-four (TOF) and double burst stimulation (DBS). Evo ked MMG responses were recorded. Patients were randomized to spontaneo us recovery (n = 20) or to assisted recovery by neostigmine (0.07 mg . kg(-1)) at varying intervals (6-50 min) from the last atracurium dose (n = 83). Results: The reversal time time from administration of neos tigmine to TOF ratio 0.7) was always < 13 min, when T-1 (first twitch in TOF) was detectable or when D-1 (first twitch in DBS) was >5%. Tota l assisted recovery time (Time from last supplemental atracurium dose to TOF ratio 0.7) increased with increasing T-1 and D-1 twitch heights (P < 0.05), The curve fitted to the scattergram with total assisted r ecovery time vs time from last atracurium supplement to neostigmine ad ministration decreased to reach a minimum after which it increased to approach the line of identity. The minimum of the curve (total assiste d recovery time 30.7 min) was reached when neostigmine was given 18.6 min after last atracurium supplement. At this time the T-1 and D-1 twi tch height average 4 and 8% respectively. If prolongation of the minim um total recov ery time of 2.5% is accepted neostigmine can be given a t T-1 and D-1 twitch height values of 0 to 8% and 4 to 15%, respective ly. Conclusion: The optimum time for neostigmine administration, takin g both the reversal time and total recover); time into consideration, is when 0 < T-1 < 8% or when 5 < D-1 < 15%. Giving neostigmine at more profound degrees of blockade prolongs reversal time, while giving neo stigmine later in the recovery phase prolongs total recovery time.