TENS

Transcutaneous electrical nerve stimulation

• TENS became a relatively common therapy in the early 1970s. It is still widely used by physical therapists and physiotherapists. [7]

Princip

• Stimulate a different type of nerve fibre (called A-beta) that carries signals relating to touch. The signals from the A-beta fibres travel to the spinal cord where they temporarily block the transmission of pain sensations to the brain – this is analogous to the ‘gate’ being closed - and so the body does not experience pain. [4]
• Thought to increase release of endorphins [4]
• Presynaptic inhibition in the dorsal horn of the spinal cord [8]
• Endogenous pain control (via endorphins, enkephalins, and dynorphins) [8]
• Direct inhibition of an abnormally excited nerve [8]
• Restoration of afferent input [8]
• The electrical stimuli on the skin preferentially activate low-threshold, myelinated nerve fibers. The afferent input from these fibers inhibits propagation of nociception carried in the small, unmyelinated C fibers by blocking transmission along these fibers to the target or T cells located in the substantia gelatinosa (laminae 2 and [3] of the dorsal horn. [8]

• Studies show marked increases in beta endorphin and met-enkephalin with low-frequency TENS, with demonstrated reversal of the antinociceptive effects by naloxone.6 These effects have been postulated to be mediated through micro-opioid receptors. Research indicates, however, that high-frequency TENS analgesia is not reversed by naloxone, implicating a naloxone-resistant, dynorphin-binding receptor. A sample of cerebral spinal fluid in those subjects demonstrated increased levels of dynorphin A. [8]

• The mechanism of the analgesia produced by TENS is explained by the gate-control theory proposed by Melzack and Wall in 1965.7 The gate usually is closed, inhibiting constant nociceptive transmission via C fibers from the periphery to the T cell. When painful peripheral stimulation occurs, however, the information carried by C fibers reaches the T cells and opens the gate, allowing pain transmission centrally to the thalamus and cortex, where it is interpreted as pain. The gate-control theory postulates a mechanism by which the gate is closed again, preventing further central transmission of the nociceptive information to the cortex. The proposed mechanism for closing the gate is inhibition of the C-fiber nociception by impulses in activated myelinated fibers. [8]

Možnosti nastavení

• Most TENS units operate in two modes, a burst or pulse mode for chronic or low-level pain, and a constant mode for acute, short-lived pain (such as a labor contraction). [2]
• Seven studies made direct comparisons between HFTENS and LFTENS. Five of seven studies could find no difference in terms of analgesic efficacy between HFTENS and LFTENS at any time point. [3]
• Conventional TENS is high frequency. High-frequency TENS is the signal that causes the pain gate to close. Low-frequency TENS is said to be more effective than high frequency for stimulating relief of endorphins. Some machines have three modes: a constant mode (high frequency, low intensity); a burst mode (low frequency, high intensity); and a modulation mode (cycling through variable frequency and pulse). [4]
• The preferred waveform is biphasic, to avoid the electrolytic and iontophoretic effects of a unidirectional current. The usual settings for the stimulus parameters used clinically are the following:
• Amplitude - Current at a comfortable, low intensity level, just above threshold
• Pulse width (duration) - 10-1000 microseconds
• Pulse rate (frequency) - 80-100 impulses per second (Hz); 0.5-10 Hz when the stimulus intensity is set high [8]
• Conventional TENS has a high stimulation frequency (40-150 Hz) and low intensity, just above threshold, with the current set between 10-30 mA. The pulse duration is short (up to 50 microseconds). The onset of analgesia with this setup is virtually immediate. Pain relief lasts while the stimulus is turned on, but it usually abates when the stimulation stops. Patients customarily apply the electrodes and leave them in place all day, turning the stimulus on for approximately 30-minute intervals throughout the day. In individuals who respond well, analgesia persists for a variable time after the stimulation stops. [8]
• In acupuncturelike settings, the TENS unit delivers low frequency stimulus trains at 1-10 Hz, at a high stimulus intensity, close to the tolerance limit of the patient. Although this method sometimes may be more effective than conventional TENS, it is uncomfortable, and not many patients can tolerate it. This method often is considered for patients who do not respond to conventional TENS. [8]
• Pulsed (burst) TENS uses low-intensity stimuli firing in high-frequency bursts. The recurrent bursts discharge at 1-2 Hz, and the frequency of impulses within each burst is at 100 Hz. No particular advantage has been established for the pulsed method over the conventional TENS method. [8]
• Patient comfort is a very important determinant of compliance and, consequently, of the overall success of treatment. The intensity of the impulse is a function of pulse duration and amplitude. Greater pulse widths tend to be more painful. The acupuncturelike method is less tolerable, because the impulse intensity is higher. [8]
• Interferential current therapy (IFC) is based on summation of 2 alternating current signals of slightly different frequency. The resultant current consists of a cyclical modulation of amplitude, based on the difference in frequency between the 2 signals. When the signals are in phase, they summate to an amplitude sufficient to stimulate, but no stimulation occurs when they are out of phase. The beat frequency of IFC is equal to the difference in the frequencies of the 2 signals. For example, the beat frequency and, hence, the stimulation rate of a dual channel IFC unit with signals set at 4200 and 4100 Hz is 100 Hz. [8]
• IFC therapy can deliver higher currents than TENS can. IFC can use 2, 4, or 6 applicators, arranged in either the same plane, for use on such regions as the back, or in different planes in complex regions (eg, the shoulder). [8]
• Percutaneous electrical nerve stimulation (PENS) combines advantages of electroacupuncture and TENS. Rather than using surface electrodes, PENS uses acupuncturelike needle probes as electrodes, with these placed at dermatomal levels corresponding to local pathology. The main advantage of PENS over TENS is that it bypasses local skin resistance and delivers electrical stimuli at the precisely desired level in close proximity to the nerve endings located in soft tissue, muscle, or periosteum. [8]

Aplikace

• The device is usually used for 15 to 20 minutes, several times a day, and is controlled by the user rather than a health professional. Pain relief may be rapid and last for days. [5]
• Usually, the electrodes are initially placed on the skin over the painful area, but other locations (eg, over cutaneous nerves, trigger points, acupuncture sites) may give comparable or even better pain relief. [8]
• The amount of output current depends on the combined impedance of the electrodes, skin, and tissues. With repetitive electrical stimuli applied to the same location on the skin, the skin impedance is reduced, which could result in greater current flow as stimulation continues. A constant current stimulator, therefore, is preferred in order to minimize sudden, uncontrolled fluctuations of current intensity related to changes in impedance. An electroconductive gel applied between the electrode and skin serves to minimize the skin impedance. [8]

Zlepšení - indikace

• At 50 Hz applied for 2 weeks was reported to improve the writing capabilities of patients with writer’s cramp (WC) [1]
• High-frequency TENS to be helpful for dysmenorrhea or painful cramps with menstruation [2]
• Mírnění porodních bolestí zad a dělohy při kontrakci [2]
• Pain Research Unit at Oxford University, published in 1997, found that evidence for it having an analgesic effect in such circumstances was weak. The unit could find no study of note showing any difference in pain intensity or pain relief scores between TENS and a placebo treatment during labour. There has not been any substantial study since, supporting its use. [5]
• Acute and chronic pain conditions, including low back pain, sciatica, neck pain, knee pain, osteoarthritis, rheumatoid arthritis, fibromyalgia, period pain, tennis elbow, phantom limb pain and the pain of childbirth. [4]
• Relieving acute and chronic pain caused by surgery, childbirth, migraine headaches, tension headaches, injuries, arthritis, tendonitis, bursitis, chronic wounds, cancer, and other problems. [7]
• According to the UK College of Anaesthetists, it isn't effective on its own as pain relief for acute moderate to severe postoperative pain [5]
• There's also some controversy as to whether TENS is effective for chronic pain, and some experts feel that more research needs to be done in this area. [5]
• TENS may be effective when used in combination with other pain treatments. [5]
• TENS is also used to deliver topical steroid medication through the skin to treat acute episodes of pain. This treatment is called Iontophoresis. The mild current causes the medication to migrate into soft tissue serving to reduce inflammation. [6]
• Some cancer patients, particularly those with mild neuropathic pain (pain related to nerve tissue damage), may benefit from TENS for brief periods of time. [7]
• Another study found that percutaneous electrical nerve stimulation—in which electrical current is transmitted through acupuncture needles instead of surface electrodes—was more effective than TENS for relieving lower back pain. [7]
• Generally, TENS provides initial relief of pain in 70-80% of patients, but the success rate decreases after a few months or longer to around 20-30%. To exclude a false-negative response, a trial of TENS for at least 1 hour should be given to confirm potential benefit from subsequent continuous use. [8]
• According to Johnson, the time from the start of stimulation to the onset of analgesia varies from almost immediate to hours (on average, 20-30 minutes in over 75% of patients and 1 hour in 95% of patients).8 The duration of analgesia also varies considerably, continuing only for the duration of stimulation in some patients and providing considerable, prolonged poststimulation relief in others. The same TENS protocol may have different degrees of antinociception in acute experimental pain compared with chronic clinical pain in patients with chronic low back pain (LBP). [8]
• Patients differ in their stimulus preferences and in their rates of compliance. In Johnson's study of compliance in patients who benefited from TENS, 75% used the device on a daily basis. Patients showed individual preferences for particular pulse frequencies and patterns, and they consistently adjusted their stimulators to these settings in subsequent treatment sessions. [8]
• Neurogenic pain (eg, deafferentation pain, phantom pain), sympathetically mediated pain, postherpetic neuralgia, trigeminal neuralgia, atypical facial pain, brachial plexus avulsion, pain after spinal cord injury (SCI) [8]
• Musculoskeletal pain - Examples of specific diagnoses include joint pain from rheumatoid arthritis and osteoarthritis, acute postoperative pain (eg, postthoracotomy), and acute posttraumatic pain [8]
• After surgery, TENS is most effective for mild to moderate levels of pain, and it is ineffective for severe pain [8]
• Chronic LBP and myofascial pain is controversial, with placebo-controlled studies failing to show statistically significant beneficial results. A literature-study report from the American Academy of Neurology recommended against the use of TENS for the treatment of chronic LBP, stating that the strongest evidence indicates that it is ineffective against this condition (Level A). [8]
• Uncertainty also exists about the value of TENS in tension headache. [8]
• Visceral pain and dysmenorrhea - TENS has been successfully applied to these conditions as well [8]
• Diabetic neuropathy - A literature-study report from the American Academy of Neurology stated that TENS is probably an effective therapy for painful diabetic neuropathy and should be considered for use in the treatment of this disorder (Level B) [8]
• angina pectoris and urge incontinence [8]
• Dental anesthesia [8]
• Assist patients in regaining motor function following stroke [8]
• Control nausea in patients undergoing chemotherapy [8]
• As an opioid -sparing modality in postoperative recovery, and in postfracture pain [8]

Zhoršení - kontraindikace

• TENS at 50 Hz worsened the clinical condition and the cortical excitability in primary writing tremor. [1]
• Pacemaker fitted;
• The use of TENS is contraindicated in patients with a demand-type pacemaker, because the stimulus output of the TENS unit may drive or inhibit the pacemaker [8]
• Epilepsy and you are using the machine alone;
• The first trimester of pregnancy (at least not around the abdomen);
• Front of your neck or over your face;
• Area of broken skin; and
• Cochlear implant hearing device [4]
• The electrodes should not be placed over the eyes, heart, brain, or front of the throat. [7]
• It may induce premature labor. [8]
• Over the carotid sinuses due to the risk of acute hypotension through a vasovagal reflex. [8]
• Over the anterior neck, because laryngospasm due to laryngeal muscle contraction may occur. [8]
• Should not be placed in an area of sensory impairment (eg, in cases of nerve lesions, neuropathies), where the possibility of burns exists [8]
• Should be used cautiously in patients with a spinal cord stimulator or an intrathecal pump [8]

NÚ

• The most common complaint is an allergic type skin reaction (about 2% of patients) and this is almost always due to the material of the electrodes, the conductive gel or the tape employed to hold the electrodes in place. [2]
• You will feel a tingling or buzzing feeling on your skin where the electrodes are placed. Some people find this sensation unpleasant. [4]

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