PREDICTION OF REVERSAL TIME AND OPTIMAL T IME FOR NEOSTIGMINE ADMINISTRATION IN ATRACURIUM BLOCKADE - COURSE OF ANTAGONISM

The aims of the study were: (1) to predict reversal time from intensiv e atracurium blockade; and (2) to determine the optimal time of neosti gmine administration during recovery from atracurium blockade, i.e., t he time at which the administration of neostigmine results in the shor test total recovery time (time from administration of last supplementa l dose of atracurium to train-of-four [TOF] ratio 0.70), and at the sa me time results in the shortest time from administration of neostigmin e to TOF ratio 0.70. Method. The spontaneous and neostigmine-facilitat ed recovery in 52 healthy women anaesthetised with thiopentone, fentan yl, droperidol, and nitrous oxide was followed. Post-tetanic count (PT C) of TOF stimulation of the ulnar nerve and mechanomyography were use d for monitoring neuromuscular transmission. The neuromuscular blockad e was induced with atracurium 0.6 mg/kg and supplemental doses of 0.15 mg/kg were given when the first twitch response in the TOF (TH1) had recovered to 20%. Neostigmine 0.036 mg/kg body weight was given at dif ferent levels of neuromuscular blockade to 37 of the patients. Results . Multiple regression analyses including pre-reversal time (time from administration of the last atracurium dose to neostigmine administrati on), PTC, weight, and age of the patients suggest that pre-reversal ti me is the best predictor of reversal time: reversal time = 27.3 min - (0.89 x pre-reversal time [min]; (SEE = 6.0 min). If pre-reversal time is unknown, PTC can be used: reversal time = 24 min - (4.5 x ln PTC) at time of reversal); (SEE = 6.8 min). Total recovery time was 47 min (SEM = 2.0 min, n = 15) in the patients allowed to recover spontaneous ly, and 29 min (SEM = 1.2 min, n = 29) in the patients reversed by neo stigmine; the difference of 18 min (SE diff 2.0 min) was significant ( P < 0.0005). The level of blockade indicated by PTC (1-24) at the time of reversal had no influence on the total recovery time. The spontane ous recovery times from reappearance of TH1 and TH1 = 10% to TOF ratio 0.70 were 29.2 min (SEM = 1.7 min) and 24.4 min (SEM = 2.6 min), resp ectively. Discussion. The results suggest that pre-reversal time is th e strongest predictor of reversal time when neostigmine is administere d during intense atracurium blockade. To achieve the optimal time-savi ng effect, neostigmine must be given 18 min (the time saved by giving neostigmine) plus 7 to 11 min (needed for neostigmine to reach its pea k effect), giving a total of 25 to 29 min before TOF ratio 0.70. As TH 1 is between 1% and 10% 25 to 29 min before TOF ratio 0.70 is reached during spontaneous recovery, the optimal level of neuromuscular blocka de for neostigmine administration in atracurium blockade is when TH1 i s between 1% and 10% Conclusion. Reversal time can be predicted as 27. 3 min - (0.89 x pre-reversal time (min), and the the optimal time of n eostigmine administration in atracurium blockade appears to be when TH 1 is 1%-10%.