Muscle electromechanical correlations during succinylcholine infusion.

The study was designed to compare the electromyographic (EMG) and evoked twitch tension (TT) responses in humans to train-of-four stimulation during neuromuscular blockade induced with a continuous succinylcholine infusion. Mean values of TT correlated well with EMG (r greater than 0.97), but several consistent discrepancies were noted. After the infusion was started but before the block was established, TT increased by up to 38%, which was accompanied by changes in the EMG signal indicative of repetitive activity. After stopping the infusion, TT but not EMG recovered to values greater than control, without changes in the shape of the EMG signal during the period of observation. This TT augmentation during recovery is consistent with a change in the contractile properties of muscle. Detection of phase II block was similar with EMG and TT (38.2 vs 41.3 min). Clinically, EMG and TT may be used interchangeably to evaluate neuromuscular blockade. In the research setting, the synchronous recording of both may help in understanding the mechanism of action of muscle relaxant drugs.