Electromedicine: Use of TENS In Pain Management
TENS has been around 40 or perhaps over 140 years, depending on which technology should be credited with bringing electrotherapy to the forefront of pain management. Recent meta-analysis indicates pain reduction from TENS averages 46%, which compares well to the 32% reduction achieved with opioids. The best therapy might be a combination, or electrochemical, approach as there are no known negative interactions between TENS and pharmaceuticals. TENS works best when the pain etiology is considered, and various protocols are attempted. This article does a fine job of reviewing historical and contemporary applications of TENS, mechanism of action, and effectiveness. The authors conclude that, when used properly, TENS has proven to be a safe and effective tool in pain management.
Daniel L. Kirsch, PhD, DAAPM, FAIS
The use of electricity in medicine has been in practice for literally thousands of years, with Aristotle cited as providing the earliest written documentation of this practice for pain relief.1 Initial electrotherapy devices were not devices at all but rather fish, such as the Torpedo electric ray fish, capable of producing 8-220 volts of electricity. Placing the fish near the feet in a wet tub or shore was purported to cure arthritis, while placing it around the head was said to cure headache. In the eighteenth century, clinical electrotherapy began to make advances with the advent of electrical storage devices such as Leyden jars and batteries, but skepticism won out, and electrotherapy for pain management did not re-emerge until the 1960s.2 Modern researchers have continued to refine these procedures and ultimately developed several modalities. Perhaps the most common of these, transcutaneous electrical nerve stimulation (TENS), has been used for approximately 40 years. In spite of, or even perhaps due to this long history of clinical utility, there has been a surprising lack of large randomized trials investigating the efficacy of TENS for pain relief. Instead, the publication history pertaining to the efficacy of TENS has been populated with smaller trials and case studies. This diversity in trial size and quality has led to two consequences for the field of electromedicine: a minor debate regarding the efficacy of TENS, and a relatively poor understanding of its mechanism of action. However, recent publications have begun to rectify the situation and will be discussed in this article.
Clinical Applications and Usage of TENS
TENS is the delivery of electrical current to peripheral nerves through intact skin using cutaneously-applied electrodes. TENS devices are designed for use either in the clinic or, in portable form, for patient self-administration. They typically consist of an electrical stimulator/power source equipped with controls to modulate frequency, current and, in some cases, waveform characteristics. Lead wires attach patient-connect electrodes to the device. In most cases, one or two sets of lead wires can be attached to a single device, allowing for the placement of two or four electrodes, respectively. Construction of the electrodes varies between and within various manufacturers, but most electrodes are self-adhesive and use a carbon- or silver ink-based conductive material. Electrode shapes and sizes vary to conform to various body parts and desired current density. In order to use the device, patients attach the lead wires to the electrodes, apply the electrodes to the specified area of the body, and connect the lead wires to the TENS device. Once this set up is complete, the patient turns on the device, selects a preset program (if available), and increases the current to a level typically described as strong but comfortable or maximal tolerable.
The applied current can vary in terms of waveform, frequency, and current level. Application of TENS at frequencies above 50Hz is referred to as high-frequency or conventional TENS, while application at frequencies below 10Hz is termed low frequency TENS. Bursts of high frequency TENS applied during a low frequency session is known as acupuncture-like or burst TENS. Different frequencies have been shown to differentially affect physiological responses to stimulation and will be discussed later in this article.
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