Nerve stimulation in regional anesthesia: theory and practice.

There is now an accumulation of extensive and varied experience with the use of electrical stimulation for verifying the close approximation of needle and nerve, and for increasing the corresponding success rate. The application of this experience has been of proven benefit in the teaching of regional anesthetic techniques, in the performing of difficult nerve blocks, and in the use of novel accesses, resulting in decreased morbidity and a reduced requirement for local anesthetic. Nerve stimulation can also be used in uncooperative patients and in anesthetized individuals or patients under the effects of CNS depressors, although the risk of intraneural injection of local anesthetic is not eliminated in such cases. Putting the accummulated knowledge into practice is not simply a question of using electrical stimulation to elicite an artificial muscle contraction. Sound knowledge of the anatomy of the area to be blocked, the muscle territory subsidiary to the nerve in question, the applied neurophysiology, and the pharmacology of the local anesthetic used are needed. This chapter reviews the most important aspects, from nerve anatomy and physiology, to electrical features of the needle, and devices used for the updated clinical application of nerve stimulation in the practice of plexus regional anesthesia.