Awake Volunteer Pain Scores During Neuromuscular Monitoring

There is a need for easy to use, reliable neuromuscular monitors (NMMs). This multicenter, prospective, unblinded study compared the discomfort associated with neurostimulation in unmedicated healthy volunteers when using the new electromyography (EMG)-based TetraGraph and acceleromyography (AMG)-based TOF-Watch NMMs. The secondary aim was to compare the repeatability of the train-of-four (TOF) ratios (TOFRs) obtained with the 2 devices.

The TOF measurements of 135 volunteers from 3 university hospitals were analyzed (age: 38.3 ± 12 years [mean ± standard deviation [SD]]; male/female ratio = 63:72). The left or right ulnar nerve was stimulated at the wrist in TOF mode with 20, 30, 40, and 50 mA stimulating current intensities with both devices in random order. The TOF-Watch used standard electrocardiography (ECG) electrodes (Red Dot; 3M Health Care) for nerve stimulation. The stimulating surface area of 1 ECG electrode is 113 mm. The piezoelectric probe was attached to the thumb, and a hand adapter was used to ensure consistency of AMG measurements. The TetraGraph uses proprietary surface strip electrodes for nerve stimulation and muscle action potential recording, whose stimulating surface area is roughly twice as big as that of standard ECG electrodes (228.5 mm). The volunteers were asked to rate the discomfort associated with neurostimulation on a 0-10 verbal numerical rating scale (VNRS) score anchored with 0 (no pain) and 10 (worst pain ever experienced). A linear mixed-effects model was used to evaluate the difference in VNRS scores between devices. P <.05 was accepted as the level of significance.

In the linear mixed-effects model, there were no differences in VNRS scores between devices at any of the stimulating current intensities, P = .38. The median (range) VNRS scores obtained with TOF-Watch and TetraGraph devices were 2 (0-7) vs 2 (0-8) at 20 mA, 3 (1-9) vs 3 (1-9) at 30 mA, 5 (1-10) vs 5 (1-10) at 40 mA, and 5 (1-10) vs 6 (1-10) at 50 mA stimulating current intensities. The mean of the 1469 TOFRs obtained with TetraGraph was 100.43% ± 7.74% (standard error = 0.2%). Due to technical difficulties, the repeatability of the TOFRs could not be determined.

Despite the different size and design of the stimulating electrodes, the 2 NMMs caused the same level of discomfort in unmedicated healthy volunteers.