A Pilot Study of Train-of-Four and Post-Tetanic Count Monitoring with the TetraGraph Electromyograph Compared to the TwitchView Monitor Electromyograph

BackgroundQuantitative twitch monitoring is recommended for avoiding residual neuromuscular blockade. Electromyograph twitch monitors are a form of quantitative twitch monitoring. The TwitchView electromyograph has been previously validated against "gold standard" mechanomyography, and may serve as a comparator for other monitors. We have previously shown that the GE electromyograph monitor overcounted twitches, frequently misinterpreting noise as a twitch. This is a pilot study to evaluate the performance of the TetraGraph electromyograph in comparison to the TwitchView electromyograph. MethodsTwitchView and TetraGraph electrodes were applied to opposite arms of patients prior to induction of anesthesia. Post-tetanic count, train-of-four count and train-of-four ratio were then measured approximately every 5 minutes during an unrestricted general anesthetic. Measurements were not made for 10 minutes following neuromuscular blocking drugs or reversal agents. ResultsEight patients were enrolled. The mean baseline train-of-four ratio was 1.02 (SD=0.04) for the TwitchView and 0.99 (SD=0.03) for the TetraGraph (p=0.22). Bland Altman analysis of all of the train-of-four ratio data found that average TwitchView train-of-four values were larger with a bias of 0.10. Train-of-four counts and train-of-four ratios were generally less when measured with TetraGraph than when measured with TwitchView.In 83% (209/253) of data pairs, the result from TetraGraph was less than the result from TwitchView and in 6% (16/253) of data pairs, the result from TetraGraph was greater than the result from TwitchView (p<0.0001). In 11% (28/253) of data pairs, the result from TetraGraph was the same as TwitchView [95%CI 7.35% 16.0%]. Evaluation of individual patient results confirmed the overall results. In some cases there were large discrepancies, such as 4 twitches reported by the TwitchView when the TetraGraph reported a post-tetanic count. ConclusionsUsers of the TetraGraph electromyograph should be aware that significant underestimation of post-tetanic-count, train-of-four count and train-of-four ratio may occur. This could result in administration of unnecessary reversal agents, excessive doses of reversal agents, or delay in extubation. We are undertaking a comparison of the TetraGraph monitor to mechanomyography to confirm the results of this pilot study.