THE STIMULATING ELECTRODES

Electrical impulses are transmitted from stimulator to nerve by means of surface or needle electrodes, the former being the more commonly used in clinical anesthesia. Normally, disposal pregelled silver or silver chloride surface electrodes are used. The actual conducting area should be small, approximately 7 to 8 mm in diameter. Otherwise, the current produced in the underlying nerve may not be adequate. The skin should always be cleansed properly and preferably rubbed with an abrasive before application of the electrodes. When a supramaximal response cannot be obtained by using surface electrodes, needle electrodes should be used. Although specially coated needle electrodes are commercially available, ordinary steel injection needles can be used. The needles should be placed subcutaneously but never in a nerve.