100 Hz-5 s tetanic stimulation to illustrate the presence of "residual paralysis" co-existing with accelerometric 0.90 train-of-four ratio-A proof-of-concept study.

Background: An acceleromyographic train-of-four (TOF) ratio of 0.90 at extubation does not prevent postoperative pulmonary complications in surgical patients receiving non-depolarising muscle relaxants. This recent observation suggests that a more selective neuromuscular transmission monitoring parameter is mandatory to detect more precisely any remaining residual paralysis. The aim of our proof-of-concept study was to evaluate, in patients receiving rocuronium, the degree of 100-Hz, 5-s tetanic fade present when the acceleromyographic TOF ratio has recovered to 0.90.

Methods: Twenty adult patients scheduled for surgery under general anaesthesia were included. Before anaesthesia induction, a TOF-Watch SX™ and a VISUAL-ITF© (a prototype monitor for recording isometric force) were positioned on both hands. After induction but before rocuronium injection, a 100-Hz, 5-s tetanus (TET0) was delivered to both ulnar nerves. Thereafter, TOF stimulations every 15 s were delivered to both arms until a TOF ratio > 0.90 was recorded; then, a 100-Hz, 5-s tetanus (TET1) was recorded on the VISUAL-ITF© monitor. The values of the tetanic parameters (force) recorded at TET0 and TET1 were compared using a Wilcoxon rank sum test.

Results: Compared to TET0, tetanic parameters of TET1 were significantly lower (median [range]): maximal force 36.4 [19.2-82.6] vs. 25.5 [5.0-42.4] Newton (p <  0.005); residual force 36.2 [18.2-82.0] vs. 5.5 [0.20-38.3] Newton (p < 0.0001) and residual force/maximal force ratio 0.98 [0.89-0.99] vs. 0.17 [0.03-0.90] (p <  0.0001).

Conclusion: Our results confirm that even when the acceleromyographic TOF ratios have recovered to above 0.90, the contralateral 100-Hz, 5-s tetanic stimulus may show tetanic fade characteristic of residual neuromuscular block, and may help improve the safety of tracheal extubation.