Precision of electromyography according to the calibration approach of neuromuscular monitoring: a randomised prospective agreement study

Purpose: Anaesthesia providers often complain that quantitative neuromuscular monitoring does not accurately assess neuromuscular function, a problem that can be mitigated by appropriate calibration. However, there are only very limited recommendations for the calibration of quantitative neuromuscular monitoring in clinical routine. Therefore, this multicentre prospective agreement study compared the precision of electromyography using three different calibration approaches. Methods: Sixty patients were assigned to one of three investigational calibration approaches: calibration before anaesthesia induction, calibration during anaesthesia induction, i.e., at loss of consciousness and state entropy < 85, or uncalibrated. All patients received electromyography calibration under deep anaesthesia on the second arm (control as recommended for research). The primary endpoint was the repeatability coefficient, which describes the fluctuation of the following train-of-four (TOF) reading. It therefore provides an estimate of the precision of a measurement method. Secondary endpoints included agreement with control calibration and pain at induction. Results: The repeatability coefficient at TOF ratios ≥ 0.8 indicated that electromyography monitoring was less precise when TOF readings were uncalibrated (0.124 ± 0.130) or with calibration during induction (0.087 ± 0.104) but was acceptable after calibration before induction (0.075 ± 0.036) compared to those measured after calibration on the contralateral arm (control: 0.072 ± 0.027, 0.061 ± 0.021, and 0.083 ± 0.063, respectively). Recall of pain at anaesthesia induction did not differ between investigational groups. Conclusion: The findings underline the importance of thoroughly performed calibration for precise TOF readings to reliably exclude residual neuromuscular blockade. Electromyography was most precise when calibration was performed under deep anaesthesia (control). If that approach is not possible in the clinical setting, our data suggest that calibration before anaesthesia induction can be considered if previously discussed with the patient. Clinical trial registration: Clinical Trials NCT04911088, registered January 6, 2021.