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TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (T.E.N.S). BY ABDULLAH RADWAN. DEFINITION. TENS is a non invasive modality for relief of pain. It is the procedure of applying controlled low voltage electrical impulses to the central nervous system through electrodes placed on the skin.
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TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (T.E.N.S) BY ABDULLAH RADWAN
DEFINITION • TENS is a non invasive modality for relief of pain. • It is the procedure of applying controlled low voltage electrical impulses to the central nervous system through electrodes placed on the skin. • The current used is either monophasic or biphasic, its wave form is either square or spike in shape.
Physiologic basis for the use of TENS: • It is the modulation of noxious impulse by an innocuous one to decrease painful sensation by 3 possible neurophysiologic mechanisms operating single or in combination. • 1. Modulation of pain in the dorsal horn of the spinal cord at the segmental level. • 2. Activation of a supraspinal inhibitory system on the nociceptive spinal neurons. • 3. A direct effect of the electrical current on the afferent stimulus in the peripheral nerve.
1. Modulation of pain in the dorsal horn of the spinal cord at the segmental level: (The gate control theory) Through stimulation of the large myelinated nerve fibers (α & β) and subsequent inhibition of pain impulses transmission through small non-myelinated nerve fibers ( C).
2. Activation of a supraspinal inhibitory system on the nociceptive spinal neurons. • The reticular cells in the brain stem are activated by somatosensory stimuli. • These stimuli may be innocuous (non-painful) in case of high frequency low-intensity TENS (traditional TENS) or nociceptive (painful) in case of low-frequency high-intensity TENS (acupuncture like stimulation).
3. A direct effect of the electrical current on the afferent stimulus in the peripheral nerve. • Through the block of nerve conduction or the change in pain threshold (increase). • However, the peripheral effect of TENS is not important in pain modulation.
INDICATIONS OF TENS • 1. ACUTE PAIN, • 2. CHRONIC PAIN, • 3. POST-OPERATIVE PAIN, • 4. PAIN OF CARDIOPULMONARY DISORDERS.
1. ACUTE PAIN, a. Acute athletic and traumatic injuries: • Mild hip strain • Shoulder contusions • Ligamentous strains b. Acute pain of arthritic origin c. Post-herpetic neuralgia d. Labour pain e. Tooth extraction
2. CHRONIC PAIN, • Rheumatoid arthritis • Osteoarthritis • Chronic myofascial pain syndromes • Chronic cervical pain as in c.s • Chronic low back pain
3. POST-OPERATIVE PAIN, • Artificial joint replacement especially hip and knee • Abdominal and thoracic surgeries • Post-operative pediatric pain • Post-operative complications as paralytic ileus.
4. PAIN OF CARDIOPULMONARY DISORDERS. • Thrombophlebitis • After thoracotomy to ↑ pulmonary function tests particularly the forced vital capacity.
CONTRAINDICATIONS OF TENS • Cardiac pacemaker • Application over carotid sinuses→ Vasovagal reflex →cardiac arrest. • Unknown progressive pathology (undiagnosed) • Malignancy • 1st 3 months of pregnancy.
PRECAUTIONS • CARE SHOULD BE TAKEN IN THE FOLLOWING APPLICATIONS: • Pregnancy (unknown effect) • Over the eyes • Internal use over mucosal linings of internal structures. • Anterior chest wall in cardiacs • Cerebrovascular accident, transient ischemic attacks, and or epilepsy. • The unreliable patient. • TENS should be kept out of the reach of children. • TENS should not be used while operating vehicles. • Application and removal of electrodes should be taken when the appliance is switched off. • Electrodes should not be placed over broken skin sites.
SIDE EFFECTS • Allergy or prickling sensation may occur during stimulation which can be avoided through: • Use of solid electrodes • Interrupt the period of stimulation • Use of corticosteroid cream 2. Unpleasant sensation 3. Laryngeal and pharyngeal ms. spasm on application to the neck. 4. Addiction to stimulation.
STIMULATION CHARACTERISTICS OF TENS • AMPLITUDE → 0 – 80 milli-ampere, • Pulse rate → 1 – 150 Hz, • Pulse duration → 30 – 250 ms, • Wave form → square or spike, monophasic or biphasic. • Stimulation with high pulse rate (50-100 Hz), narrow pulse width (30- 75 ms) and low amplitude (10- 30 MA) will produce comfortable tingling sensation but not ms. Contraction.
METHODS OF TENS APPLICATION • TRANSCUTANEOUS: • By a trans-cutaneous nerve stimulator to the skin surface at the site of pain or any site related to it. • Used by the patient and monitored by the physical therapist.
2. PERCUTANEOUS: • Used to evaluate the possible value of an implantable nervous system stimulator. • Carried out by needle electrodes inserted through the skin near the peripheral nerve or epidural or sub-arachnoid's space for spinal cord stimulation. If pain is controlled by percutaneous application, implantation of electrodes is performed. • Performed only in physician office, clinic or hospital outpatient department.
3. IMPLANTATION Discussed
ELECTRODES 1. Mostly, Carbon filled silicone electrodes: • Electrodes require application of conductive gel and are fixed to the skin by adhesive tape. 2. Solid electrodes (Karya electrodes): • large molecular weight polysaccharide mixed with hydric alcohol. • Hydrophilic and adhere to the skin when wet. • Less incidence of skin irritation.
TECHNIQUE OF STIMULATION • The patient should recognize the device and the electrodes, then place it over his hand and forearm to recognize the sensation of electrical stimulation. • Then, the patient should put the electrodes over the painful area with the pulse width and frequency should be at the lowest level. • Then, gradual increase of pulse width and frequency to the maximum tolerated non painful level. • If pain is not relieved, the process should be repeated on another day or after 30 min. • If pain failed to be relieved after 3 consecutive trials, the patient should be treated by another different type of therapy. • If pain is relieved, patient is instructed how to use the apparatus for prolonged times at home.
ELECTRODES PLACEMENT • Mostly, pair of electrodes is placed over the painful area. • Nerve root irritation → electrodes placed paravertebrally over the affected spinal cord segments. • Muscular or bony pain → electrodes placed over myotomal or sclerotomal distribution. • Peripheral nerve injury or peripheral neuropathy → electrodes placed over the peripheral nerve proximal to site of pain. • Post-herpetic neuralgia → electrodes placed over the contralateral region corresponding to the painful region. • Bilateral stimulation of painful regions or spinal cord segments is indicated in LBP syndromes.
DURATION AND FREQUENCY OF TREATMENT • 30 – 60 min, twice daily or 3 to 5 per week. • In chronic conditions → patient should be instructed how to use the apparatus at home.
TENS devices • Very safe • Compact • Portable • Easy to operate • Non invasive • Non addictive • Does not produce any adverse irreversible change in the body.