EDROPHONIUM ANTAGONISM OF ATRACURIUM DURING ENFLURANE ANAESTHESIA

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Abstract
To determine the influence of enflurane on the ability of edrophonium to antagonize atracurium block, dose-response curves were constructed for edrophonium in the presence of 0%, 1% and 2% enflurane, and for 2% enflurane discontinued at the time of administration of edrophonium. One hundred ASA Physical Status I or II patients (four groups of 25), selected randomly and undergoing elective surgery, received atracurium 0.5 mg kg-1, with thiopentone, nitrous oxide and enflurane. Supplementary doses of fentanyl were given if needed. Train-of-four (TOF) stimulation was applied every 12 s, and the force of contraction of the adductor pollicis muscle was recorded. When first twitch height (T1) had recovered spontaneously to 10% of initial value, edrophonium 0.1, 0.2, 0.4 or 1 mg kg-1 was administered by random allocation. Enflurane concentrations remained constant, except that enflurane was discontinued in 50% of the patients who had received 2% enflurane. Monitoring was continued for at least 10 min, at which time T1 and TOF ratio (T4/T1) were measured. The ED80 for T1 recovery depended on the dose of enflurane: 0.08 (SEM 0.03), 0.21 (0.096) and 0.42 (0.18) mg kg-1 for 0%, 1% and 2% enflurane, respectively (P < 0.005). With enflurane 2% discontinued, the ED80 was 0.095 (0.050) mg kg-1 (P < 0.02 compared with 2% enflurane). The ED50 for TOF responses were 0.13 (0.05), 0.46 (0.10) and 1.04 (0.38) mg kg-1 for 0%, 1% and 2% enflurane, respectively (P < 0.001). With 2% enflurane discontinued, the ED50 for TOF was 0.17 (0.12) mg kg-1 (P < 0.05 compared with 2% enflurane). It is concluded that, even when given at the same degree of spontaneous recovery, the effect of edrophonium is markedly attenuated by enflurane.