Spontaneous recovery from rocuronium measured by mechanomyography during 100- or 200-Hz tetanic stimulations compared to normalized train-of-four with acceleromyography.

Neuromuscular block recovery was evaluated using high-frequency tetanic ulnar nerve simulations compared to normalized train-of-four (NTOF) in anesthetized patients. Under intravenous general anesthesia, we compared rocuronium-induced neuromuscular recovery using 5 s 100- and 200-Hz tetanic stimulations via isometric mechanomyography to acceleromyographic NTOF in 20 consenting patients. The primary outcome was the comparison by Student's t-tests of 100- and 200-Hz tetanic fade ratios (residual force at the end of the contraction / maximal force reached during the 5 s) before rocuronium administration and at different recovery levels. The secondary outcome was the quantification of any significant fade occurring with 100- and 200-Hz stimulations after reaching the acceleromyographic NTOF ratio of 0.9 during subsequent stages of spontaneous recovery until their fade ratios exceeded 0.9. During early (TOF count ≥ 1) and intermediate (NTOF ratio ≥ 0.5) stages of recovery, both 100- and 200-Hz tetanic fade ratios were similarly low. However, during late recovery when NTOF ratio ≥ 0.9, 200-Hz stimulation induced a significantly deeper muscular fade than 100-Hz (tetanic fade ratio 0.20 ± 0.23 vs. 0.64 ± 0.29, P < 0.001). The delays between the recovery of NTOF ratio 0.9 and 100- or 200-Hz tetanic fade ratio 0.9 were 7.7 ± 7.1 and 43.6 ± 14.6 min, respectively. In anesthetized humans, mechanomyographic 200-Hz tetanic stimulation detects lighter levels of residual paralysis than NTOF and 100-Hz tetanic stimulation during a valuable additional period. Registered in the ClinicalTrials.gov Registry NCT05474638 on July 15th 2022.