THE AGREEMENT BETWEEN ADDUCTOR POLLICIS MECHANOMYOGRAM AND FIRST DORSAL INTEROSSEOUS ELECTROMYOGRAM - A PHARMACODYNAMIC STUDY OF ROCURONIUMAND VECURONIUM

The agreement between evoked adductor pollicis mechanomyogram and firs t dorsal interosseous evoked electromyogram (EMG) was evaluated during a pharmacodynamic study of rocuronium and vecuronium. In the first pl ace the effective doses of rocuronium producing 50% and 90% block (ED( 50) and ED(90), respectively) were established in 32 neurolept anaesth etized patients from the adductor pollicis mechanomyogram ram and the first dorsal interosseous EMG area and amplitude. Secondly, limits of agreement between the two methods were evaluated from the mean differe nce between methods +/-2 s.d. in 20 patients during onset of block fol lowing 2 x ED(90) of rocuronium and vecuronium, and during recovery fr om the last supplementary dose of 1/2 x ED(90). Limits of agreement sh ow how much the EMG may be above or below the mechanomyogram. No diffe rences were found between mechanomyographical and EMG based ED(50) (0. 20 mg kg(-1)) and ED(90) (0.3-0.32 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 mec hanomyogram during onset compared to 12-17% during recovery. The EMG T OF ratio lagged behind that of the mechanomyogram by 0.05 at TOF ratio s below 0.50. No difference was found between methods at a TOF ratio o f 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 t he amplitude and the area of the EMG were better than between the mech anomyogram and the EMG. Evaluation of the rime courses of action showe d that rocuronium had a faster onset of action than vecuronium (1.8 mi n compared to 2.8 min) while duration of action and reversal were simi lar. In conclusion, the first dorsal interosseous EMG amplitude and ar ea can be used to assess rocuronium and vecuronium block.