Performance of acceleromyography with a short and light TOF-tube compared with mechanomyography: a clinical comparison

BACKGROUND: Disturbances in the thumb's movement interfere with the functioning of acceleromyography in many clinical settings. The short and light (SL) train-of-four (TOF)-Tube is a new version of a rigid tubular device that was designed to protect the thumb from external disturbances during surgery, even when the hand is not accessible by the anaesthesiologist.

OBJECTIVE: To compare the precision and performance of acceleromyography performed with the aid of the SL TOF-Tube (AMGTT) with standard isometric mechanomyography (MMG).

DESIGN: Simultaneous arm-to-arm comparison of both methods in the same anaesthetised patient.

SETTING: A monocentric study, performed from September 2007 to June 2008.

PATIENTS: Nineteen ASA I to II patients scheduled to undergo lower limb orthopaedic surgery under general anaesthesia.

INTERVENTION: Neuromuscular transmission monitoring during baseline, onset and spontaneous recovery of rocuronium-induced neuromuscular block.

MAIN OUTCOME MEASURES: Initial baseline and repeatability coefficients were assessed during 10 consecutive measurements of the first twitch height (T1) and TOF T4/T1 ratio and compared using a z test. The spontaneous recoveries of defined blockade levels (onset, T1 25% of initial calibration and TOF ratio 0.9) were compared in terms of duration and intensity. Agreement between both techniques was assessed by the Bland-Altman method.

RESULTS: The mean ± SD control TOF ratios were 98 ± 1% (MMG) and 103 ± 2% (AMGTT). The repeatability coefficients were higher (P < 0.001) and the onset was longer (mean 0.44 min) (P < 0.001) when they were measured by AMGTT. The recoveries of T1 25% and TOF ratio 0.9 were not significantly different between the two methods, and the limits of agreement were in the usual range of contralateral comparisons (-19 and +24% for TOF ratio 0.9).

CONCLUSION: Compared with mechanomyography, acceleromyography performed with the aid of an SL TOF-Tube offered acceptable precision and equivalent performance during neuromuscular block recovery.