About TENS Unit

February 8, 2020
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What is a TENS unit?

A TENS unit is a battery-operated, technology-based, non-invasive, pain management system, which utilizes an electrical signal to relieve pain. It is a drug-free pain reducing technique. It can be administered by the patient and does not need any particular skill.

The manufacturer’s user guide or a ‘how to use it’ advice from your doctor is good enough. The TENS unit is very portable, almost the size of a smartphone and has simple to use keypads.

It is a handy tool which is convenient and easy to use. You can carry along when travelling. TENS treatment requires no consumables, hence no recurring expenses, except replacing the pads. If carefully used, these pads can last longer.

Various models of the TENS unit are available in the market. The variations being in the features, the number of pads, capacity and price. You can select the most appropriate model from the available options. This product is popular in Europe and USA and is gaining popularity in India too.

It is available in clinical models and personal use models. Clinical models are used by the physiotherapist/Doctors. The discussion in this article concerns the individual model.

The MERCK manual also acknowledges the use of TENS unit as one of the pain management techniques.

How does a TENS unit work?

Primarily, the personal TENS unit consists of a unit, wires to connect the pad to unit, pads, and charger to charge the unit. The main unit is very compact and handy.

The electrodes stuck on the back of the patient. The unit delivers controlled electrical impulse through the connected wires to the pad. The pad is attached firmly onto the body, at the place, where it pains.

The electrical impulse travels through the skin to the nerves and stimulates them. This nerve stimulation or, sometimes known as electrical nerve massaging mitigates the sensation of pain.

Depending upon the setting of frequency, pulse duration and intensity, one may get a tingling sensation, a pricking feeling or muscle twitches.

These setting are a matter of personal judgement and depends on how the body reacts to the impulses. The Tens unit needs to recharge and once charged, can be used on the go.

A recent development in the range of the personal model is the wireless model. They do not have any wires going from the unit to the pads. The advantage is these can be worn very discreetly. No wire entanglements when not in use. Can be worn under your clothes, no cut wires or loose connection issues. But replacement and spare pads need to be bought from the manufacturer, which may be costlier. But overall, a good concept and can be considered if you are looking to purchase a TENS unit. Some brands may offer the facility of hot fomentation (heat therapy) before the actual electrical stimulation begins. It facilitates faster relief.

Why use a TENS unit?

It is non-invasive, can be self-administered. As the pain reduces, the pain-relieving medications can be reduced. It is not habit-forming. In most of the cases does not have any reaction. A TENS unit works well for chronic as well as acute pain. You can use in conditions like:

  1. Neck pain
  2. Shoulder pain
  3. Mid back pain
  4. Lower back pain
  5. Knee pain
  6. Ankle pain
  7. Menstrual pain
  8. Arthritis
  9. Post-operative pains
  10. Sports injuries.
  11. Hip pain.
  12. Sciatica

A consensus on the time of therapy is about 15- 20 minutes at one go, and it can be used several times a day. In some cases, the treatment can be for a longer duration of 1 to 2 hours. The placement of the pads is a very critical step which determines the effectiveness of the treatment.

TENS Unit Pad Placement

Pads can be placed:

  1. Over the affected area, proximal and distal to the epicentre of the pain.
  2. Placing on acupuncture points (If you knows these point locations on the body)
  3. The pads should be at least one inch apart.

Avoid placing pads on:

  1. Chest and back (upper) simultaneously
  2. Over the temples
  3. Over the eyes
  4. On the front of the neck
  5. Sides of the neck
  6. Open wound
  7. Varicose veins

The pads should be at least one inch apart.

Before placing the pads on the skin, the skin should be wiped clean, so that the electrical transmissions can happen uninhibited. Application of gel over the skin can be still more effective.

The unit should be switched on only after the pads have been placed on the pain area. Set the controls at low intensity and low pulse duration initially as you feel a slight tingling. Gradually increase the setting to feel a strong pulse, but no discomfort. If there is pain or muscle twitch, reduce the setting to a tolerable and comfortable level. A micropore tape can be applied over the pads to ensure close contact. Once the session is over, first switch off the unit and then detach the pads.

How does a TENS unit relieve pain?

There are two diverse theories to explain how does electrotherapy work.

Gate control theory

It is believed to be an advanced theory. There is a neural mechanism in the spinal cord, which is very instrumental in sending pain signals to the brain and carrying instructions from the brain to the affected part. How the signals are transmitted to the brain depends very much on the fact, whether the neural mechanism (gate) is closed, open or semi-open. The frequencies of the electrical signals emanating from the TENS unit disrupts the normal flow of message signal from neurons to this gate (these signals are also electrical), and hence the gate remains closed, and no pain signal is transmitted to the brain. Thus, the patient experience relief.

This explains why relief is experienced in headache, or backache when it is massaged. The massage pressure generates a dull pain and this pain of massage, though dull, blocks the sharp headache, and there is a relief.

Similarly, the tingling of the nerve ends at the affected part, because of TENS stimulation, block the sharp muscular pain. It has to be understood that the TENS unit does not treat the underlying cause of pain. It just helps alleviate pain.

Endorphine release theory

The electrical stimulations on the TENS UNIT help to release endorphin in the body, which are like natural morphine. This endorphin because of their biochemical reactions, can block the pain signals from reaching the brain. This theory is based on the similar lines as to how drugs alleviate pain.

How long can you use the TENS unit?

The time period for which you can use TENS is a matter of user’s convenience and requirement.

But generally, as a guideline:

For chronic pain, one can use it about 5 times for 15- 30 minutes, at the appropriate setting.

For acute pain, the time can be increased to 60 minutes and used 4 times a day.

Regular medications can continue when you are using TENS.

Though the specifications vary according to the manufacturers and the model, the general parameters are discussed here.

Typical specification of TENS device:

  1. WEIGHT: The weight of the unit could vary from a very compact 50 gm to a standard size weighing 250 gms.
  2. SIZE: The smallest version could be 6 x 5 x 2 cm and the larger ones could be 12 X 4 X 9 CM.
  3. PULSE AMPLITUDE: 1-50Ma (variable)
  4. PULSE DURATION: 1-1000microseconds (variable)
  5. PULSE FREQUENCY: 1-250 PPS (Adjustable)
  6. BATTERY: 9V chargeable

Side effects of using a TENS unit

The TENS therapy unit is quite safe for pain treatment and hence has been approved by USFDA, the regulator for health care products for over the counter sale. However, in some cases some side effects or reactions may be seen:

Skin burns

Using the unit for too long on high intensity may result in burnt skin, under and around the electrodes. It is advised to treat the skin before applying the pad again to the same area. Common burn lotions and ointments should serve the purpose.

Aggravated wounds

If the pads are placed too close to the open wound, it might aggravate it. Hence pads should never be placed over or close to open wounds.

Skin irritation

Very sensitive skin can get irritated because of using TENS. It is advisable to do a small spot test to ensure whether your skin can tolerate the TENS stimulation.

Muscle soreness

Prolonged use, particularly at a higher setting, may fatigue and muscles and develop pain. Do not use the unit until the muscle recovers fully of soreness.

Facial nerve damage

Never use the pads above your neck and on the front of the neck. Incidences of facial nerve damage have been reported if the pads are used on the face.

General precautions

  • Its effect on foetuses is not yet determined medically. So pregnant mothers should avoid it.
  • People who have epilepsy should avoid using TENS
  • Persons with a pacemaker or any other electronic implants should also not opt for this therapy, as it may interfere with the working of the pacemaker/implants.
  • Should not be applied directly over the spinal cord
  • Should not be used on tumours.

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