TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (TENS) UNIT THERAPY

WHAT IS TENS 

Definition: Transcutaneous electrical nerve stimulation (TENS) unit is defined as low frequency analgesic physio-therapeutic modality which is designed based on control theory (i.e Gate theory of pain).

WHAT IS TENS THERAPY

TENS Therapy is the application of Electrotherapy modality or machine called transcutaneous electrical nerve stimulation (TENS) unit, which is using low frequency current mainly used for management and control of pain, both acute and chronic type.

GATE THEORY OF PAIN

Gate theory of pain is the theory which was described by Melzack and Wall in 1965, this theory explains about a pain-modulating system in which a neural gate present in spinal cord can open and close. therefore modulating the perception of pain.

So this TENS unit modality was designed based on this "Gate theory of pain" for the therapeutic purpose of management and control of pain, both acute and chronic type.

PRODUCTION OF TENS

To produce the therapeutic effect of gate theory of pain well, we must increase A fiber transmission without increasing C fiber transmission. How this can be done, it is duty of engineering acuity and industrial ingenuity. However, researchers found that A fibers respond to greater extent than other fibers, to phase input i.e waveforms that are sensed by the body as continous and generally contain multiple phases of positive/negative modes. but in C fibers apparently react best to continous waveforms and those sensed by the body as continous.

PARAMETERS OF TENS

(1) Pulse shape: rectangular type impulses

(2) Pulse frequency: 2Hz - 600Hz, but frequency 150Hz is commonly used

(3) Pulse width: 100JS, generally 50ps - 30ps use

(4) Intensity: 0 - 60milliamps (mA), a satisfactory intensity till tingling sensation. 

TYPES OF TENS

(1) High TENS or Conventional TENS: It is a high frequency and low intensity stimulation.

• Frequency: 100 - 150Hz
• Intensity:     12 - 30mA
• Pulse width: 100 - 500ps.

This type of TENS is mainly used for management of superficial pain both acute and chronic.

(2) Low TENS or Acupuncture TENS: Is is a high intensity and low frequency stimulation.

• Frequency:  1 - 5Hz
• Intensity:     300mA
• Pulse width: 100 - 500ps.

(3) Burst TENS: It is also known as wave train because this type of TENS has series of pulses, repeated 1-5 times per second. 

• Frequency: 50 - 150Hz

This type of TENS is mainly used for pain relief.

(4) Brief TENS: It is a TENS with long duration pulses 0.2ms.

• Frequency: 100Hz
• Intensity:    20 - 50mA

This type of TENS is mainly used for local pain relief and should not be applied for more than 15 minutes.
(5) Modulated TENS: This type of TENS was designed with modulating system in pulse length, frequency and amplitude of pulse. the main purpose for designing this type of TENS by manufacturers is to prevent accommodation of stimulation or to improve patient tolerance. 

METHOD OF APPLICATION OF TENS

Most of the TENS units available in market provide a literature on the machine as well as the electrode placement diagrams. but for better therapeutic response the following steps has to be followed:

• First select the sites where electrodes are to be placed
• Observe the site: for any contraindication like wound, dermatological condition or any cut. 
• Place the electrode with ample quantity of coupling medium (Ultrasound jelly)
• Fix electrodes on the site by elastic band or adhesive tapes
• Turn on the machine
• Turn on the amplitude knob and increase the intensity of current until the patient feels the tingling sensation.
• Turn the frequency knob and increase frequency i.e pulse rate
• Set the timer for required time. if the machine does not offer timer facility then use stopwatch.

 INDICATIONS OF TENS 

• Acute pain of osteogenic, myogenic, neurogenic origin
• Chronic pain of osteogenic, myogenic and neurogenic origin

TENS can never be used in abdominal pain

CONTRAINDICATIONS OF TENS

(1) TENS should never be applied over the eye, laryngeal or pharyngeal muscles, neck and head region

(2) TENS should not be applied on the neck of patient with cerebrovascular accidents.

(3) On the neck or head region of epileptic patient 

(4) On the chest region of patient with cardiac diseases

(5) Never applied on mucosal membrane

(6) On the shoulder region of patient with demanded type of pacemaker

PRECAUTIONS TO BE TAKING DURING APPLICATION OF TENS ON THE PATIENT BODY

• Over the insensitive skin 
• On the open wounds
• Do not use TENS on a patient with demand type pacemaker in place
• TENS can be used in labour pain, but not in pregnant patient