Transcutaneous Electrical Nerve Stimulation PDF

Transcutaneous Electrical Nerve Stimulation Transcutaneous Electrical Nerve Stimulation Transcutaneous electrical nerve stimulation (tens) is the application of low frequency current in the form of pulsed rectangular currents through surface electrodes on the patient’s skin to reduce pain. A small...

Transcutaneous Electrical Nerve Stimulation Transcutaneous Electrical Nerve Stimulation Transcutaneous electrical nerve stimulation (tens) is the application of low frequency current in the form of pulsed rectangular currents through surface electrodes on the patient’s skin to reduce pain. A small battery operated machine is generally used to generate current, which have specific stimulatory effect. The effect and use of TENS depends upon gate control theory and pain modulation.Pain is an unpleasant disturbed sensation, which accompanies the activation of nociceptors. Pain is a subjective phenomenon with multiple dimensions. Nociceptors are the sensory receptors, which carries pain stimulus. Any physical, chemical, thermal or mechanical stimulus like heat, cold or pressure activates these nociceptors. These are free nerve endings found in all body tissues. They carry pain stimulus to the higher centers. Once a nociceptor is stimulated, it releases a neuropeptide, which initiates the electrical impulses along the afferent fibers toward the spinal cord. These afferent fibers are of two types: A Delta fibers: Fast conducting myelinated fibers, which conducts with a velocity of 5–30m/s. C-fibers: Slow conducting small diameter non myelinated fibers, which conducts with a velocity of 2–5m/s. TENS apparatus FIRST ORDER OR PRIMARY AFFERENT FIBERS: First order or primary afferent fibers transmit impulses from the sensory receptors to the dorsal horn of the spinal cord. First order neurons include A- alpha, A-beta , A-delta and C-fibers. A-alpha and A-beta fibers are characterized by having large diameter afferents and A-delta and C-fibers are characterized by having small diameter afferents. SECOND ORDER AFFERENT FIBERS: The second order afferents are nociceptive specific. Second order afferent fiber carry sensory impulses from the dorsal horn of the spinal cord to the brain.A nociceptive neuron transmits pain signals. Its cell body lies in the dorsal root ganglion. A-delta and C-fibers transmits the sensation of pain. Fast pain is transmitted over the faster-conducting A-delta afferent neurons and originates from receptors located in the skin. Slow pain is transmitted by the C afferent neurons and originates from both superficial (skin) and deeper (ligaments and muscle)tissue. Most nociceptive second-order neurons ascend to higher centers along one of three tracts: (1) Lateral spinothalamic tract, (2) Spinoreticular tract, and (3) Spinoencephalictract, with the remainder ascending along the spinocervical tract or as projections to the cuneate and gracile nuclei of the medulla. Approximately 90% of the wide dynamic range second-order afferents terminate in the thalamus. Pain gate control The pain gate theory was first postulated by Ron Melzack and PatWall in 1965. This theory was later modified in 1982. Afferent input is mainly through posterior root of the spinal cord and all afferent information must pass through synapses in the substantia gelatinosa and nucleus proprius of the posterior horn. It is at this level that the pain gate operates and presynaptic inhibition by TENS works. Mechanism of pain gate control: Nociceptive afferent enters the spinal cord via the dorsal root and make synapses either with interneuron or with second order neuron (called as transmission cells or T cells) in the substantia gelatinosa in dorsal horn of spinal cord. The second order neuron crosses the midline of the spinal cord and transmit information to the higher centers via the lateral spinothalamic tract. These second order ascending neuron synapse with third order neuron in the nuclei of thalamus. The third order neuron carries the noxious stimulus to the cerebral cortex. Modulation of transmission Modulation of transmission of pain can be achieved by altering the excitability of this pain pathway. The excitability of this pathway can be altered by other neurons(substantia gelatinosa) in the dorsal horn. The substantia gelatinosa (SG) cells have inhibitory influence on the T cells. This mechanism is called as presynaptic inhibition Also the nociceptive afferent sends collaterals to the substantia gelatinosa (SG) which inhibits the substantia gelatinosa cells when these nociceptive afferents are activated, these causes inhibition of substantia gelatinosa (SG) cell activity which will further inhibit the mechanism of presynaptic inhibition thus allowing the nociceptive stimuli to reach the higher centers. Also low threshold large diameter mechanosensitive afferent have excitatory influence on substantia gelatinosa (SG) cells. Their activation causes excitation of substantia gelatinosa (SG) activity which in result causes increased presynaptic inhibition blocking the transmission at T cells thus closes the gate for nociceptive stimuli to travel up to the higher center. This is the site where the pain gate operates.In addition to these input to SG cells from peripheral afferent there are descending influences on Transmission cells (T cells) which came principally from higher center such as periaqueduct gray matter PAG (midbrain) and raphe nucleus (medulla) these both have excitatory influence on the substantia gelatinosa (SG) cells activity thus have ability to reduce pain transmission. These pathways are thought to exert their effect on Substantia gelatinosa (SG) cells by release of neurotransmitters such as noradrenaline and 5-hydroxyl tryptamine. Under normal conditions periaqueduct gray matter (PAG) and raphe nucleus are inhibited by neurons from other areas of the brain. During pain the inhibition on periaqueduct gray matter (PAG) and raphe nucleus (RN) is removed by influence of the limbic system thus allowing PAG and RN to exert its effect at substantia gelatinosa of dorsal horn of the spinal cord. The TENS stimulates the large diameter myelinated fibers as these are highly sensitive to electrical stimulation and quickly conduct the electrical impulse to the spinal cord. The A-delta and C-fibers are unable to pass the painful stimulus to spinal cord earlier than the large fibers. This mechanism by which the nociceptor fibers are prevented from passing on their message to the spinal cord is called as presynaptic inhibition Types of TENS 1. High TENS: In this high frequency and low intensity electrical stimulation is applied. The stimulation will cause impulse to be carried along with the large diameter afferent fibers and produces presynaptic inhibition of transmission of nociceptive A-delta and C-fibers at substantia gelatinosa of the pain gate. It is used for acute pain. Frequency — 100–150 Hz Pulse width — 100 and 500 ms Intensity — 12–30 mA 2. Low TENS: In this low frequency and high intensity electrical pulses are applied, it gives a sharp stimulus and like a muscle twitch. As the nociceptive stimulus is carried toward the cerebrum, its passage through the midbrain will cause the periaqueductal area of gray matter and raphe nucleus to interact to release the opiate-like substances at cord level. The encephalins and endorphins released have the effect of blocking forward transmission in the pain circuit. It is used for chronic pain. Frequency — 1–5 Hz Pulse width — 100 and 500 ms Intensity — 30 mA or more 3. Burst TENS: In this high frequency, short pulse, high intensity electrical current is used.Burst TENS is a series of impulse repeated for 1–5 times per second. Each train (burst) lasts for about 70 ms. The benefits for the Burst TENS are that it combines both the conventional and acupuncture like TENS and thus provide pain relief by the both routes. Methods of Treatment Electrode placement: TENS electrode can be placed over— 1. Area of greater intensity of pain. 2. Superficial nerve proximal to the site of pain. 3. To the appropriate dermatome. 4. To the nerve trunk trigger point. A number of treatment methods may be used depending upon the severity of the problem. 1. TENS can be used for a single daily treatment of 40 minutes duration. 2. Portable TENS can be used continuously for 24 hours. 3. TENS can be used in night, e.g. for the treatment of phantom limb pain Indications for Use TENS can be used for the treatment of: 1. Chronic pain syndrome 2. Phantom limb pain 3. Reflex sympathetic dystrophy 4. Postoperative pain 5. Obstetric pain. Dangers and Contraindications 1. Continuous application of high TENS may result in some electrolytic reaction below the skin surface. 2. TENS is contraindicated in patients having cardiac pacemakers may be because of possible interference with the frequency of pacemaker. 3. TENS should be avoided in first three months of pregnancy. 4. TENS should be avoided in hemorrhagic conditions. 5. TENS should be avoided over open wounds, carotid sinus, over the mouth, near eyes , etc