Comparison of neuromuscular block measured by compressomyography at the upper arm and electromyography at the adductor pollicis muscle in obese and non-obese patients: An observational study.

Quantitative neuromuscular monitoring is traditionally evaluated at the adductor pollicis muscle. By contrast, the TOF-Cuff compressomyograph evaluates neuromuscular block (NMB) at the upper arm. However, compressomyography has not been fully validated against other monitoring entities. This study evaluates the agreement between NMB measured by compressomyography at the upper arm and electromyography at the adductor pollicis muscle during various levels of neuromuscular block in patients with and without obesity. NMB was measured at the upper arm by compressomyography (TOF-Cuff) and by electromyography (GE-NMT) at the adductor pollicis. Prospective, multicenter, observational study. Secondary and tertiary care hospitals' operating theatres. 200 non-obese and 50 obese patients. During onset and offset of deep (post-tetanic-count 1-15 twitches), moderate (Train-of-Four-count 1-3 twitches) and shallow (Train-of-Four-ratio 0.01-1.0) depths of NMB were measured in obese and non-obese patients. The bias and limits of agreement of both devices were calculated using a Bland-Altman analysis for repeated measurements. Data obtained during spontaneous recovery (i.e. without the use of reversal agents) were used in the primary analyses. Data from enrolled patients yielded 942 paired post-tetanic-counts, 1175 paired train-of-four-counts and 1574 paired train-of-four ratios during spontaneous recovery. In non-obese patients, mean bias (95% CI) between the two devices was 3.405 (2.294 to 4.517) during deep NMB; -0.023 (-0.205 to 0.160) during moderate NMB and 0.312 (0.287 to 0.338) during shallow NMB. In obese patients, bias was -0.170 (-2.872 to 2.531); 0.178 (-0.202 to 0.558); 0.384 (0.299 to 0.469) for deep, moderate and shallow NMB respectively. There is variable disagreement between the level of NMB measured at the upper arm by compressomyography and at the adductor pollicis muscle measured by electromyography, throughout the various stages of NMB in obese and non-obese patients. Recovery of NMB on compressomyography preceded recovery on electromyography, which may have consequences for reversal and extubation decisions in clinical practice.

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