Electrode polarity and peripheral nerve stimulation

Abstract

During peripheral nerve stimulation, the active, negative electrode should be placed at the wrist over the ulnar nerve for maximal twitch response of the thumb. Increasing the distance of the electrode from the ulnar nerve lessens the current density and reduces the twitch height. If the polarity of the electrodes is unknown, the electrodes can be tested by alternately reversing polarity to determine which pair produces maximal muscle response. Perhaps the manufacturers of peripheral nerve stimulators should identify the anode and cathode connections. Failure to appreciate differences in polarity might result in muscle responses that could lead the anesthesiologist to overestimate the effect of the muscle relaxant during maintenance as well as to underestimate reversal following antagonist administration.