The role of the Touch TENS machine from Tenscare in the management of pain
TENS (Transcutaneous Electrical Nerve Stimulation) is used as one of the tools in the armoury of most chronic pain clinics.
If successful, TENS helps patients to alter their pain behaviour. The rapid response produced by TENS gives users a strong feeling that they can take action to control their pain.
Long term users report a wide range of benefits:
- less pain interference with work, home, and social activities
- increased activity level and pain management
- decreased use of other therapies (e.g., physical therapy, occupational therapy, chiropractic)
- decreased use of narcotics, tranquilizers, muscle relaxants, nonsteroidal anti-inflammatory drugs and steroids
However, different centres report a wide range in success rates, from 50 -82%. Standards of expertise and patient instruction vary widely between centres. As the management of chronic pain is transferred to Primary Care, the resources available for instruction and review may become diluted.
How can we give individual users the greatest chance of success with TENS?
Our assumptions were:
- Many patients are confused by, or unable to understand, the choices offered them on standard units
- Most patients do not try more than 3 settings before giving up.
- Preset Programs offer the simplest way of using TENS
- A majority of patients will find that one of the Presets will work for them
- If the patient feels comfortable with TENS, he is more likely to use it
- Patient training is much simpler
With the idea of producing a TENS unit that was both very easy to use and effective – giving the maximum chance of good compliance – Tenscare designed a TENS unit with preset programmes and a minimum number of controls.
We used digital technology to give accuracy, repeatability, and a simple user interface. Since successful use of TENS implies use for many hours of every day, we also tried to design a product that was both durable, and modern and attractive in appearance.
Parameter Selection Most authorities agree that TENS works in two ways:
Pain Gate (High frequency >80Hz)
A strong stimulation of the sensory nerves inhibits transmission of the pain nerves at the spinal level. -Pain relief may be obtained for several hours, but stops as soon as the unit is switched off.
Endorphin release (Low frequency<10Hz)
Repeated muscle twitch stimulates the descending pain inhibitory pathways to generate endorphin production. -This is less comfortable than high frequency, cannot be used for long periods because it can lead to muscle fatigue, but gives a carry over of pain relief for several hours after use.
Frequency and Pulse Width settings
Frequency (Rate) Settings
No studies have been published that examine whether any settings for Pain Gate between 50 and 100 Hz may be more effective. The only relevant published study concluded that, given a free choice, patients seem to choose a wide range of settings independent of cause of pain for reasons of comfort which “may not be related to mechanisms specific to the pain system.”
Pulse Width (Duration) Settings
Longer duration pulses are more likely to stimulate all types of nerve fibre, so longer duration gives a stronger, less comfortable, sensation. At least 150 uS is required to stimulate larger muscles (for maximal stimulation 300uS could be required).
Preset vs Adjustable
Birmingham City Hospital carried out an uncontrolled clinical audit of 100 patients after one year of use: 50 using a very simple device with only two settings – High Frequency and Burst, and 50 using conventional units with a wide range of settings, with similar training given to both groups. Responses showed that patients with the simpler machine used it for longer periods, and reported greater pain relief and greater reduction of painkillers.
Intensity and Waveform Waveform should be “balanced”.
- This means that a negative current is sent back in the opposite direction immediately after the pulse. This ensures that there is no build up of electrolytes under the pads which could cause skin irritation
- Waveform should be comfortable. A “spikey” waveform feels itchy and is less effective
- The unit has to be powerful enough to give a strong sensation in the least sensitive areas like the back, but there is no evidence that more power than this gives more than a brief improvement in pain relief. Around 60mA is the normal maximum required
- Some older analogue TENS units have non-linear intensity controls, so that it is easy to accidentally set the intensity painfully high. We chose to use 15 equal intensity steps – not too many presses to reach the desired intensity, but predictable and repeatable
- More information on Touch TENS from Tenscare