Neuromuscular effects of i.a. infusion of lignocaine in man

Neuromuscular effects of lignocaine during and after i.a. infusion were studied in healthy adult patients, using evoked electromyography. Supramaximal, paired stimuli were applied to the ulnar nerve with variable intervals between the two stimuli. The amplitude of the hypothenar muscle action potential to the second component of the paired stimulus (test response) was compared with that evoked by the first component (conditioning response). During and after i.a. infusion of lignocaine, there were marked decreases of the test response at intervals from 7 to 100 ms after the conditioning stimulus, although the decreases of the conditioning response were slight or negligible. The finding of decreased test responses coincided with the results obtained with tetanic stimulation such as pronounced fade and only slight post-tetanic potentiation. Differences between these findings and those found with muscle relaxants were compared, and it was concluded that the mechanism responsible for these results might be attributed to an effect of lignocaine on the motor nerve terminal.