The agreement between adductor pollicis mechanomyogram and first dorsal interosseous electromyogram. A pharmacodynamic study of rocuronium and vecuronium.

The agreement between evoked adductor pollicis mechanomyogram and first dorsal interosseous evoked electromyogram (EMG) was evaluated during a pharmacodynamic study of rocuronium and vecuronium. In the first place the effective doses of rocuronium producing 50% and 90% block (ED50 and ED90, respectively) were established in 32 neurolept anaesthetized patients from the adductor pollicis mechanomyogram and the first dorsal interosseous EMG area and amplitude. Secondly, limits of agreement between the two methods were evaluated from the mean difference between methods +/- 2 s.d. in 20 patients during onset of block following 2 x ED90 of rocuronium and vecuronium, and during recovery from the last supplementary dose of 1/2 x ED90. Limits of agreement show how much the EMG may be above or below the mechanomyogram. No differences were found between mechanomyographical and EMG based ED50 (0.20 mg kg-1) and ED90 (0.30-0.32 mg kg-1), respectively. The first EMG train-of-four (TOF) response overestimated block at 25% recovery and underestimated block at 75% and 90% recovery by only 3-7%. Limits of agreement suggested that the EMG may be 7-8% above or below the mechanomyogram during onset compared to 12-17% during recovery. The EMG TOF ratio lagged behind that of the mechanomyogram by 0.05 at TOF ratios below 0.50. No difference was found between methods at a TOF ratio of 0.75. Limits of agreement indicated that the EMG TOF ratio may be 0.12-0.15 above or below that of the mechanomyogram. Agreement between the amplitude and the area of the EMG were better than between the mechanomyogram and the EMG. Evaluation of the time courses of action showed that rocuronium had a faster onset of action than vecuronium (1.8 min compared to 2.8 min) while duration of action and reversal were similar. In conclusion, the first dorsal interosseous EMG amplitude and area can be used to assess rocuronium and vecuronium block.

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