Percutaneous electrode guidance: a noninvasive technique for prelocation of peripheral nerves to facilitate peripheral plexus or nerve block.

BACKGROUND AND OBJECTIVES: Typically, peripheral nerve block is done by approximating nerve location, usually by use of anatomical landmarks. Precise nerve location has been done by needle exploration. A new method, percutaneous electrode guidance (PEG) of the block needle, was performed. A transcutaneous stimulating cylindrical electrode was used to indent the skin, locate the underlying nerve, and guide a block needle near it.
METHODS: PEG was used to prelocate the desired nerve or neural plexus by use of a shielded cylindrical electrode with a 1-mm-diameter conductive area of skin contact at the distal end, the center of which contained a 22-gauge (1/2 mm) hole, which precisely matched a shielded conventional block needle. Transcutaneous stimulation began at less than 10 mA and was decreased to minimal amperage that elicited the desired motor response. Electrode position was fixed, and electrode current was discontinued. A shielded 22-gauge block needle was advanced through the electrode guide to near the underlying nerve. Initial needle current was only 0.5 mA. Local anesthetic was injected to block the targeted nerve or nerves. Standard sensory/motor testing was performed at 20 minutes.
RESULTS: Nine upper or lower extremity blocks were performed on 7 patients. All were successful. Minimal stimulating currents were 1.3 to 8.2 mA for transcutaneous electrode stimulation and 0.20 to 0.70 for needle stimulation. Needle depth was 0.4 to 1.1 cm beyond the electrode tip and correlated with minimal electrode stimulating current.
CONCLUSIONS: A smooth, metal-tipped electrically shielded skin electrode probe can be used to comfortably and accurately indent the skin over a desired nerve or plexus, define its anatomical course, and subsequently guide a block needle near it.