An observational study comparing the performance of TOF-Cuff with TOF-Scan monitoring during anaesthetic induction in clinical routine

Introduction
Neuromuscular monitoring by acceleromyography assesses the effects of non-depolarising neuromuscular blocking agents used during anaesthesia induction to optimise intubation conditions. A new type of neuromuscular monitor, TOF-Cuff, integrates electrode stimulation into a blood pressure monitoring cuff. Comparisons of this device with TOF-Scan, considered a clinical standard acceleromyography device, have not been published.

Material and methods
This prospective, observational study was approved by the Ethics Committee East Switzerland (BASEC-nr. 2016-02044), and patients’ consent was obtained before inclusion. The study’s aim was to compare TOF-Cuff with TOF-Scan by measuring the duration from the administration of a neuromuscular blocking agent to a train-of-four (TOF) ratio of 0%. After anaesthesia induction, atracurium was administered (0.5 mg kg-1) and TOF ratios were recorded every 15 seconds using the two devices simultaneously. Patients were grouped according to body mass index (< or ≥ 30 kg m-2).

Results
Twenty-five non-obese and twenty-five obese patients were included. In non-obese patients, bias was –3 s (± 21.2; limits of agreement –44.7 to 38.4; P = 0.702). In obese patients, bias was –20 s (± 35.0; limits of agreement –88.6 to 48.6; P = 0.0139). Large intra-individual differences of up to 60 seconds were detected even in non-obese patients.

Conclusions
A significant systematic difference in the time to reach a TOF ratio of 0% was found when using the two devices in obese patients. In non-obese and obese patients, there were large intra-individual and clinically relevant differences. The two devices cannot be used interchangeably.