EDROPHONIUM ANTAGONISM OF ATRACURIUM DURING ENFLURANE ANAESTHESIA

To determine the influence of enflurane on the ability of edrophoniumto antagonize atracurium block, dose—response curves wereconstructed for edrophonium in the presence of 0%, 1% and 2%enflurane, and for 2% enflurane discontinued at the time ofadministration of edrophonium. One hundred ASA Physical StatusI or II patients (four groups of 25), selected randomly andundergoing elective surgery, received atracurium 0.5 mg kg^–1,with thio-pentone, nitrous oxide and enflurane. Supplementarydoses of fentanyl were given if needed. Train-of-four (TOF)stimulation was applied every 12 s, and the force of contractionof the adductor pollicis muscle was recorded. When first twitchheight (T1) had recovered spontaneously to 10 % of initial value,edrophonium 0.1, 0.2, 0.4 or 1 mg kg^–1 was administeredby random allocation. Enflurane concentrations remained constant,except that enflurane was discontinued in 50% of the patientswho had received 2% enflurane. Monitoring was continued forat least 10 min, at which time T1 and TOF ratio (T4/T1) weremeasured. The ED₈₀ for T1 recovery depended on the dose of enflurane:0.08 (SEM 0.03), 0.21 (0.06) and 0.42 (0.18) mg kg^–1 for0%, 1% and 2% enflurane, respectively (P < 0.005). With enflurane2% discontinued, the ED₈₀ was 0.095 (0.050) mg kg^–1 (P< 0.02 compared with 2% enflurane). The ED₅₀ for TOF responseswere 0.13 (0.05), 0.46 (0.10) and 1.04 (0.38) mg kg^–1for 0%, 1% and 2% enflurane, respectively (P < 0.001). With2% enflurane discontinued, the ED₅₀ for TOF was 0.17 (0.12)mg kg^–1 (P < 0.05 compared with 2% enflurane). It isconcluded that, even when given at the same degree of spontaneousrecovery, the effect of edrophonium is markedly attenuated byenflurane.