Quantitative neuromuscular monitoring with train-of-four ratio using sonomechanomyography (SMMG): Toward more sensitive evaluation of neuromuscular blockade.

In the post-anesthesia care unit, there is a high occurrence of residual neuromuscular blockade, which puts patients at risk of negative consequences such as hypoxia. Assessment based on the train-of-four ratio (TOFR) has been used to avoid residual neuromuscular blockade when the TOFR is greater than 0.9, measured at the adductor pollicis muscle (APM). The most commonly used quantitative neuromuscular monitoring (QNM) modalities include acceleromyography (AMG) and electromyography (EMG). However, the poor user-friendliness of current QNM methods hinders their widespread adoption. To overcome this, we developed a new monitoring method using ultra-fast ultrasound imaging to generate a two-dimensional map of muscle transient motion, i.e., sonomechanomyography (SMMG). SMMG of the APM and AMG of the thumb were used to get the TOFR of 20 normal adults. The results showed no significant difference between the left and right hands for both AMG and SMMG TOFR, with p-values larger than 0.05. In addition, the mean accuracy of SMMG TOFR (0.6% relative error) was higher than AMG (1.4% relative error). Moreover, the Bland-Altman plot showed that all the difference values were within the limits of agreement and the mean bias was 0.02, indicating that the two methods had a very good agreement. In particular, using SMMG did not require additional calibration before testing. Overall, the results demonstrated that the method has the potential as a new QNM approach for further clinical studies to benefit patients in need. To demonstrate its clinical potential, further studies are required to evaluate this method in patients during and post-anesthesia.