Chronic pain and disabling muscles aches is one of the most common reasons why most people seek physical therapy. Although the history of physical therapy is as old as almost 140 years, in the last few decades a lot of machines and devices are also constructed on the physical therapy principles and techniques that are of great help in managing chronic pain symptoms in office and home based settings. TENS (Transcutaneous electrical nerve stimulation) is perhaps one of the most effective physical therapy technique used in alternative medicine today.
TENS refers to the transcutaneous passage of electric currents in a pre-determined frequency across peripheral nerves. A current of a particular wavelength and intensity is delivered via electrodes that are attached to the skin. The frequency or intensity can be controlled manually.
TENS are broadly classified as conventional TENS and low-frequency TENS on the basis of the frequency used in the procedure. Conventional therapy uses a current frequency of 50Hz or above; whereas in low- frequency TENS, a much lower frequency is used (less than 10Hz). Different frequencies have different effects on the physiological perception of pain by modulation of electric nerve signaling across nerve fibers.
The working principle deals with excitation of peripheral nerves in an attempt to suppress the nerves that carry pain signals to the brain. This can be achieved if the device stimulates nerve fibers with a higher frequency in comparison to pain nerve fibers.
Transcutaneous electrical nerve stimulation is widely used in managing acute pain at home or in a clinical setting. The most preferred use is in labor pain. Although not very effective, TENS is one of the preferred pain management techniques used during the later stages of labor and women who prefer to give vaginal birth without anesthesia can get benefits from TENS.
TENS is one of the safest and most risk-free methods available today to treat chronic pain of diabetic neuropathy and musculo-skeletal injuries refractory versus ordinary pain medications. TENS is also used in the management of osteoarthritis pain by physical therapists.
TENS is very effective in the management of acute pain soon after major surgeries and accidents to reduce the dose of morphine or other prescription pain-killers.
Chronic pain may be functional, post-surgical or neuro-muscular in origin. Unfortunately, there are limited options for the management of pain in most cases. Traditionally, the most popular management strategy adopted by most physicians and general public is OTC pain killers. For moderate to severe pain, over-the-counter NSAIDs (Non- steroidal anti- inflammatory drugs) are ineffective and more potent opoids are needed for relief; however, opoids and other pain medications have a number of complications including addiction potential, phenomena of tolerance and multi- organ damage.
Use of TENS provides long lasting pain relief that is free from complications. A Meta-analysis suggested that TENS provides a 43% reduction in chronic pain cases as opposed to just 23% reduction with opoid use. For safety and optimal benefits, it is important to consider these points: Do not put TENS electrodes directly onto eyes or around peri-orbital region due to substantial risk of an alarming rise in intra- ocular pressure that may lead to pain or even damage to visual apparatus. It is contraindicated to apply electrodes over a tumor or malignancy as the electric current may stimulate the growth of the tumor. Never put electrodes on the anterior aspect of the neck as the risk of vaso-vagal reflex is very high that may culminate in hypotension, cerebral ischemia and other complications. Putting electrodes on wounds, open or abraded skin or abscess should also be avoided. For best results, always consult a physical therapist about the proper use of TENS devices for individual or home use.
TENS can be given as an adjuvant therapy with other pain medications in patients with chronic pain (in terminal stages of cancer, chemotherapy induced pain and neuromuscular abnormalities) along with potent pain killers. This helps in reducing the dose required to produce pain-relief while decreasing the risk of addiction or tolerance.
For optimal benefits, it is mandatory to consider the etiology of pain and accordingly other interventions should also be considered simultaneously (since TENS work best as an adjuvant therapy).
How Does it Work?
TENS is administered through electrical stimuli sent to specific nerves in the skin. The electrical currents used in the process are painless, and carry no side effects that have been recorded.
The currents stimulate nerve fibers in the skin’s nerve endings (transcutaneous means through the skin) and warm the skin. This warmth eases stiffness and increases mobility for lower amounts of pain, and also promotes the production of hormones called endorphins. These endorphins act as natural pain killers as well.
What Equipment is Needed for TENS?
To deliver the current to the skin, the patients uses various skin patches that direct the current to a specific area of the skin. A current-generating pack called the stimulator creates the currents and then the patches direct the currents to the soft tissue in the body.
These units are portable and battery powered. A patient is able to direct his or her own pain relief with the use a stimulator by turning it on when pain relief is needed. Patients rent or purchase the units for long term use.
A physical therapist applies the patches and coordinates the strength of the receptors and currents. The therapist may also choose to deliver some kinds of surface, or topical, medications. Through a technique called iontophoresis, the electrical current assures that the medication moves into the tissue for lower levels of pain and inflammation.
What Pain Is Alleviated by Using TENS?
The technique is commonly prescribed by physicians to reduce lower back pain, arthritis pain, myofascial pain, bladder incontinence, and pain resulting from surgery. The system is not always effective for every pain, so a trial usage is a great idea.
What Intensity of Electrical Stimulation is Effective?
The default settings for the stimulators is a comfortable amplitude, just below the threshold of pain, with the pulse width or duration between 10 and 1000 microseconds, and the pulse rate, or frequency, at 80 to 100 impulses per second when the machine is set on high.
The ideal setting for each patient has to be determined by trial and error over time. In addition to the settings on the stimulator, the patient also experiments with the location of the electrodes.
While they are often placed directly over the areas that are in pain, sometimes they are positioned over trigger points or the primary nerves in the body, and patients report pain relief that is as great or even greater relief than placing them on the painful area.
Research trials looking at the effectiveness of nerve stimulation have so far been inconclusive. Further large studies are needed to clarify the precise role and effect of using TENS. However, TENS machines have proved to be a popular form of pain relief with some people. As with many forms of treatment, the effect can vary from individual to individual, even with the same condition.
How TENS machines work?
Transcutaneous means through the skin. TENS machines deliver small electrical pulses to the body via electrodes placed on the skin. TENS machines are thought to affect the way pain signals are sent to the brain. Pain signals reach the brain via nerves and the spinal cord. If pain signals can be blocked by the tiny electrical shocks from the TENS machine, then the brain will receive fewer signals from the source of the pain.
Instructions for using a TENS machine?
There are various types and brands of machines. Always follow the manufacturer’s instructions supplied with your machine.
Some general points:
• TENS EMS are designed so that you can move around with them working. You can tuck the machine into a pocket or clip it on to a belt
• Before placing the electrode pads on the skin make sure the machine is switched off
• Test the machine by holding the pads between the fingers and then carefully turn it on. You should feel a tingling sensation
• Make sure the skin where the pads are applied is clean and dry and there are no cuts, grazes or areas of skin irritation
• Place the pads either side of the pain. Use either self-adhesive pads or flexible rubber pads which should be completely covered, on the surface to be applied to the skin, with a thin layer of conductive gel. The pads should not be put within an inch (2-3 cm) of each other. Your physiotherapist or doctor will show you where to put the pads
• Fix the pads to the skin with tape if you intend moving around
• Set the pulse rate to the required setting (about 100 Hz is about right to start with)
• Switch on the machine slowly and turn it up gradually until you feel a tingling sensation. The sensation needs to be quite strong but not uncomfortable. After a few minutes the sensation will start to drop away slightly. This is called accommodation. When this happens, turn the machine up slightly and then leave it for the rest of the time in use. Do not turn it up too high, as this can cause over-stimulation which may make pain worse. There should be no muscle contraction
• At the end of the session turn the machine off and disconnect the electrodes from the machine. If you intend using TENS again later there is no need to remove the electrode pads from the skin. Simply tuck the wires out of the way and carry on as normal
• Check that the pads or tape do not irritate the skin. If the skin is red you may need to use a different type of pad, contact gel or tape
• The machine should be used for at least 45 minutes but can be used for up to 12 hours before the electrodes need to be cleaned and re-sited
• When you have finished using the machine for the day, carefully remove the pads from the skin and clean the skin with ordinary soap and water. Do not pull directly on the wires to remove the pads. If there is any redness or irritation from the pads or tape then the next time you use the machine use a different area of skin
• If you use rubber pads, clean off the conducting gel with mild soap and water and rinse them well. Do not wash the self-adhesive type of pad.