TetraSens electrode array has two proximal stimulating electrodes, one recording electrode and one reference electrode. The application is easy and quick. The electrode array is for single-patient use in order to avoid cross contamination. The electrodes can be applied on either hand, with the stimulation electrodes over the ulnar nerve at the wrist and the evoked response recorded from any of the hand muscles; typically, either the muscle at the base of the little finger ADM (abductor digiti minimi muscle), or, more commonly, from the muscle at the base of the thumb, AP (adductor pollicis muscle). TetraSens can also be placed on the FDI muscle (first dorsal interosseous). When the hand is inaccessible, the posterial tibial nerve (flexor hallucis brevis muscle), can be used for NMT monitoring.