Optimum time for neostigmine reversal of atracurium-induced neuromuscular blockade

Purpose: The aim of the study was to determine the optimum time for administration of neostigmine during recovery from atracurium-induced neuromuscular blockade. Methods: The study comprised 103 patients anaesthetised with midazolam, fentanyl, thiopentone, halothane, and nitrous oxide. Relaxation was induced with atracurium 0.5 mg . kg(-1) and maintained with supplements of 0.15 mg . kg(-1). The ulnar nerve was stimulated with train-of-four (TOF) and double burst stimulation (DBS). Evoked MMG responses were recorded. Patients were randomized to spontaneous 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 neostigmine 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%. Total 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 recovery time vs time from last atracurium supplement to neostigmine administration decreased to reach a minimum after which it increased to approach the line of identity. The minimum of the curve (total assisted 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 twitch height average 4 and 8% respectively. If prolongation of the minimum total recov ery time of 2.5% is accepted neostigmine can be given at T-1 and D-1 twitch height values of 0 to 8% and 4 to 15%, respectively. Conclusion: The optimum time for neostigmine administration, taking 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 neostigmine later in the recovery phase prolongs total recovery time.