Onset of action of mivacurium chloride. A comparison of neuromuscular blockade monitoring at the adductor pollicis and the orbicularis oculi.

BACKGROUND

The optimal site for monitoring neuromuscular blockade for intubations facilitated with mivacurium chloride has not been established. The primary purpose of this evaluation was to determine the difference in onset of neuromuscular blockade between the orbicularis oculi and adductor pollicis in patients administered mivacurium chloride. We also evaluated intubating conditions when intubation was timed to maximal neuromuscular blockade at either the orbicularis oculi or the adductor pollicis. The results for patients administered mivacurium chloride were compared with those for a control group administered succinylcholine.

METHODS

In a double-blind randomized design, the time to loss of the compound muscle action potential at the orbicularis oculi and adductor pollicis was monitored in 20 patients administered mivacurium chloride and ten patients administered succinylcholine. After administration of mivacurium chloride (0.15 mg.kg-1), ten patients underwent tracheal intubation at maximal depression of the orbicularis oculi (group 2) and ten patients at maximal depression of the adductor pollicis (group 3). In an additional ten patients the trachea was intubated 60 s after administration of succinylcholine (1 mg.kg-1) (group 1, control). Intubation and evaluation of conditions was performed by one investigator blinded to patient treatments.

RESULTS

Loss of compound muscle action potential at the orbicularis oculi and adductor pollicis was more rapid in group 1, and intubation was completed at 86 +/- 26 s. In the patients administered mivacurium chloride, the orbicularis oculi compound muscle action potential was lost 3 min earlier than the adductor pollicis compound muscle action potential. Subsequently, intubation was completed at 134 +/- 50 s in the orbicularis oculi group, whereas the time to intubation was 321 +/- 57 s in the adductor pollicis group. There was no significant differences in intubation conditions between the mivacurium chloride groups.

CONCLUSIONS

When monitoring 95% twitch height depression of the orbicularis oculi muscle, intubation can be accomplished in approximately 2 min after administration of mivacurium chloride (0.15 mg.kg-1). Because intubating conditions were comparable to the patients administered succinylcholine or intubated during monitoring of the twitch height depression of the adductor pollicis, we believe that optimal site for monitoring during intubation using mivacurium chloride is the orbicularis oculi muscle.