Comparison of Electromyography Derived Train-of-Four Ratios of the Adductor Pollicis and Abductor Digiti Minimi Muscles and their Comparison to Acceleromyography Derived Train-of-Four Ratios

Reka Nemes, M.D., J. Ross Renew, M.D. Department of Anesthesiology, Mayo Clinic Florida

BackgroundThis pilot study investigated a new electromyography- (EMG) based neuromuscular monitor, the TetraGraphTM (Senzime AB, Uppsala, Sweden, Fig. 1) in the operating theater. The TetraGraphTM uses specifi cally designed surface strip electrodes (TetraSensTM, Senzime AB, Uppsala, Sweden, Fig. 2) for ulnar nerve stimulation and compound muscle action potential recording from the adductor pollicis (mAP) or the abductor digiti minimi muscles (mADM).

MethodsTwo TetraGraphTM devices were attached to the patient, one on each arm. One device was attached to the thenar eminence and the thumb to monitor the muscle response of mAP. The other monitor was attached to the hypothenar eminence and 5th fi nger to monitor the mADM. This arm also served for acceleromyography (AMG) monitoring (IntelliVue NMT, Philips, Amsterdam, the Netherlands) of the thumb. After the induction of anesthesia, the three devices were calibrated to defi ne supramaximal current intensities, then started in train-of-mode (TOF) mode and ran automatically in an alternating fashion. The EMG measurements on the two arms were performed at the same time and the AMG measurements were timed halftime between two consecutive EMG stimulations. From the start of measurements until the disappearance of muscle twitches due to neuromuscular blockade, the stimulation interval was 20 sec, then it was set to 1 min. At the end of the procedures, before the administration of the reversal agent, the interval time was reset to 20 sec. We aimed to compare the correspondence of the two hand muscles’ EMG TOF ratios (%), and to examine the agreement between the EMG and AMG measurements.

ResultsAfter Mayo Clinic IRB approval (IRB# 17-06680), and gaining informed consent, eleven patients {age: 58.1 ± 15 years (mean ± SD), male: n=5, female: n=6, BMI: 30.3 ± 5.7)} were enrolled in the study. The charge in µC (defi ned as the product of current intensity, in mA, and pulse width, in msec) required for supramaximal stimulation was lower for mADM than for mAP (11.3 ± 4.3 vs. 13.6 ± 3.7 μC, respectively), though this did not reach statistical signifi cance (p=0.27). The maximal baseline muscle action potential amplitude was higher in mAP than in mADM (13.33 ± 7.6 vs. 9.94 ± 1.8 mV, respectively, p=0.198). The onset of neuromuscular block was faster at the mADM in 72.7% of cases than in mAP. The medians (interquartile range) of baseline TOF ratio measurements were statistically similar in the EMG measurements {mAP: 99.0 (97.3-100.0) vs. mADM: 98.0 (96.0-100.0), p=0.075}, yet both EMG derived mAP and mADM baseline TOF ratios were signifi cantly lower than AMG mAP TOF ratios {112 (105-123), p<0.001}, Fig. 3. The recovery EMG TOF ratios of the two muscles showed good correlation (R = 0.716, p<0.001, Fig. 4) with a bias of -8.36 (95% CI = -28.59 to + 11.88, Fig. 5); however, the correlation was weaker with AMG-derived mAP TOF ratios (for mAP EMG R = 0.659, p<0.001; for mADM EMG R=0.547, p<0.001).

Figure 1

The TetraGraphTM electromyography-based quantitative neuromuscular monitor.

Figure 2

The TetraSensTM electromyography surface electrode

References1. Philips S et al. Anaesth Intensive Care 2012; 40(4):690-6.

2. Hemmerling TM et al. Can J Anaesth. 2004; 51(8):795-800.

3. Katz RL. Br J Anaesth. 1973; 45(8):849-59.

© 2018 Mayo Foundation for Medical Education and Research

DiscussionThe TetraSensTM electrodes of TetraGraphTM are designed to measure the neuromuscular function of the adductor pollicis and abductor digiti minimi muscles. Our preliminary results are in accordance with previous investigations [1-3] reporting that these two muscles cannot be used interchangeably for electromyography monitoring of intraoperative neuromuscular function; mADM has a faster onset of neuromuscular blockade and faster recovery of neuromuscular function than mAP. We plan to expand this pilot study to 100 patients to ensure statistical power of our investigation.

Figure 5Bland-Altman plot of adductor pollicis (mAP) and abductor digiti minimi (mADM) derived recovery electromyography train-of-four ratios (%).

Figure 4Linear regression of adductor pollicis (mAP) and abductor digiti minimi (mADM) derived recovery electromyography train-of four ratios (%).

Figure 3Box plot diagram of baseline train-of-four ratios (%) obtained with electromyography (EMG) at the adductor pollicis (mAP) and abductor digiti minimi muscles (mADM) and obtained with

acceleromyography at the adductor pollicis muscle. Box plots represent medians and interquartile ranges, whiskers represent 10th and 90th percentiles, dots represent outlier values.