- October, 2015
For those of you who I have not yet met, I am Kevin Scanlan, Vice President of Clinical Services at Checkpoint Surgical. In this edition of Decision Point we will review the advantages of the Checkpoint
biphasic waveform, as compared to direct current (DC) stimulation employed by other hand held nerve stimulators. Recently we met with several surgeons to discuss their very real concern regarding nerve palsy after surgery and how intraoperative nerve stimulation using the Checkpoint Stimulator/Locator can be employed to help avoid it. One surgeon expressed the belief that all nerve stimulators create nerve fatigue and repeated use of any stimulating device will cause the nerve to “go to sleep” for a period of time. Another surgeon disagreed stating that this wasn’t necessarily the case. That while all direct current stimulators will cause diminished nerve response over time, Checkpoint’s biphasic waveform is significantly safer, allowing repeated and continuous stimulation to tissue without affecting corresponding motor response during the procedure.
In this Decision Point we’ll take a brief look at why the two different forms of electrical stimulation cause such a difference in response – both initially and after repeated stimulation. Direct current causes a single twitch of the muscle innervated by the nerve. In a DC stimulator the probe must be tapped on and off the nerve in order to get multiple twitches; one twitch of the muscle every time the probe touches the nerve tissue. Simply put, the DC stimulator current flow causes potentially damaging electrochemical changes at the probe and does not result in a sustained stimulation of the nerve and contraction of the muscle it innervates. The metal probe on a direct current stimulator is slowly changing the chemistry of the immediately surrounding tissue. The pH (acidity) of the tissue is changed by the hydrolysis of the blood and body fluids.
Additionally, DC stimulation results in a single “twitch” of muscle when the current is first applied and sometimes another when the current is stopped. In many cases, this can make it difficult to confirm which specific nerve was stimulated. DC stimulation can be safe, but only when applied for a very brief instant (no more than a second) and even then,
quickly causes diminished nerve response with repeated use. If overused on a nerve, or contacting a nerve for more than one second, the result may be an extended nerve palsy or nerve damage after the patient awakens.
Checkpoint’s biphasic stimulus, on the other hand, is a waveform that has no net direct current. Checkpoint stimulates the nerve while maintaining recruiting efficiency by having a large fast pulse (Cathode Phase or “stimulating phase”) that stimulates the nerve and followed that by a smaller CS-9094-MKT-104-A September 2015 amplitude Anode Phase or “recovery phase” that lasts longer and recovers all the charge introduced by the larger fast pulse. In essence the biphasic waveform is taking out the same amount of electrical charge that it’s putting in, thus delivering a net zero charge to the tissue. Therefore, the Checkpoint Stimulator allows for frequent and continuous stimulation without diminished nerve response.
Moreover, Checkpoint’s pulsing (AC) current, employing a biphasic waveform, can generate a fused or sustained muscle contraction rather than just a single muscle twitch. AC Current flow (or, more precisely, repeating pulses of current) results in repetitive twitches that fuse together into a sustained Muscle contraction. This allows not only more definitive confirmation of nerve identification but also intraoperatively, allows the surgeon to actually move muscles and attached tendons and bones.