Electrical stimulation and ultrasound in regional anesthesia

Nerve localization can be achieved by eliciting either a functional needle endpoint (e.g. mechanical paresthesia, motor response to electrical stimulation) or anatomical endpoint (e.g. periarterial injection, ultrasonographic imaging). The most widely used method to determine a functional endpoint is by the use of electrical nerve stimulation. Increasingly, ultrasonographic guidance is being used to determine anatomical endpoint in conjunction with or in place of electrical nerve stimulation. Peripheral nerve stimulation utilizes an oscillating square wave (pulse) of electrical current at a given frequency, current amplitude, and pulse duration that are very accurate in locating peripheral nerves. Nerve stimulation is very specific but has been lacking in sensitivity. Newer technology, including sequential electrical nerve stimulation, maintains the accuracy while increasing the sensitivity of this modality. Ultrasonographic guidance can also be very specific and sensitive for nerve location. Compared to electrical nerve stimulation, compact portable ultrasound units are much more expensive. To date, no differences have been shown in block success or complication rates between the two techniques. It is important to maintain proficiency in the use of both electrical nerve stimulation and ultrasonographic guidance for optimal practice and teaching of peripheral nerve or plexus anesthesia. Ideally both techniques may often be used in conjunction, enabling the practitioner and patient the benefits of each technique during simultaneous use.