Peripheral nerve stimulators have widespread among anaesthesiologists and remain a popular technique. However, in commercial devices, the user has to manually adjust stimulus intensity. Thus, the aim of this study is to propose a method that allows automating the current intensity control. An earlier nerve stimulator prototype was modified to add an accelerometer and an sEMG module. The choice of these two sensors is aimed at the possibility of observing the mechanical and electrical responses of the muscle contraction evoked by the stimulation. The tests were performed in two steps. The first step was to observe how the sensors behave during stimulation and muscle contraction. The second step was to implement a control algorithm and to validate the automation technique. Comparing the two methods, no significant differences were found on procedure time (manual: 12.5 ± 2.3; automatic: 11.6 ± 1.9; ρ =0.380) and blockade latency time (manual: 11.6 ± 1.1; automatic: 11.9 ± 1.2; ρ =0.524). Comparing needle-nerve distance in manual or automatic mode, no significant differences were found for 1.0 mA, 0.8 mA, 0.5 mA and 0.3 mA. We conclude that the technique for automating the current intensity update, using accelerometer and/or electromyography, is satisfactory. Furthermore, we conclude that the use of the accelerometer alone is sufficient for detection of muscle contraction.
Keywords: Nerve stimulator; accelerometer; automatic control; electromyography; regional anaesthesia.