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ZMPCZM016000.11.18 Pain Control with TENs


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ZMPCZM016000.11.18 Pain Control with TENs

  1. 1. Pain Control With Transcutaneous Electrical Nerve Stimulation ROGGER SCUDDS BRUCE LAI B .Sc ., M .C.S.P., M.H.K.P.A., Lecturer in Physiotherapy, Hong Kong Polytechnic Physiotherapy '83 Student, Hong Kong Polytechnic Transcutaneous Electrical Nerve Stimulation (TE.N.S.) is being used widely in the management of pain. Pain is a complex phenomenon and any modality that seeks to modify it directly must take into account both physiological and psychological considerations. Gate control theory, the endorphins and a non-opiate descending pain suppression mechanism are described in brief and some of the psychological considerations are introduced . The characteristics of the T.E.N.S. machin e are discussed and an attempt is made to relate the stimulus parameters of intensity, frequency and pulse width to the management of acute and chronic pain. Electrode placement strategies are described and examples are given for their use with commonly encountered pain syndromes. In conclusion, the needfor patient control ofthe machine is emphasised along with the integration of TENS. with other treatment modalities in the overall management ofthe patient. INTRODUCTION Transcutaneous Electrical Nerve Stimulation (T .E .N .S .) is a seemingly simple piece of therapeutic apparatus that is increasingly being used in the control and management of pain . (Taylor et . .al, 1981 ; Solomon et al, 1980) However, the nature of pain itself makes the effective application of T .E .N .S . more complex than it would first appear . Pain has been described as "an unpleasant experience which we associate with tissue damage or express in terms of tissue damage, or both ." (Merskey, 1978) . It is obvious, therefore, that pain is not merely a sensation which is perceived in direct relationship to the stimulus intensity, but is also intimately connected with the emotional state and the psychological set of the patient (Sternbach, 1978) . Thus, in seeking to modulate pain in any way, the therapist must not only be aware of the physical state of the patient but also the emotional state and the mental attitude . Pain can be modified by cognitive manipulation, change of mood, or by various physical means, such as opiates, analgesics or other agents which act on the peripheral or central nervous systems . T .E .N .S . is a noninvasive technique of electrical stimulation of the peripheral nervous system . It has recently emerged as a distinct therapeutic modality in the control of both acute and chronic pain . Studies (Wolf et al, 1978) have looked at the equipment's characteristics e .g . intensity, pulse width and frequency, and their relationship to treatment effectiveness . However, it seems clear that without ,n basic understanding of the nature of pain, it will not be possible to approach the patient with full confidence and knowledge of the technique's capabilities and limitations . Volume 5, 1983. GATE CONTROL Since its first proposal in 1965 by Melzack and Wall, the original gate control theory of pain has undergone much revision . However, as a basis for understanding a possible mechanism for the sensory modulation of pain it is still widely accepted . Briefly, it proposes that a neural mechanism in the dorsal horn of the spinal cord can act as a controlgate to bar or admit afferent noxious messages from the peripheral nervous system to the central nervous system . Large diameter fibre afferent stimuli, i .e . non-noxious stimuli, would tend to close the gate to the transmission of noxious stimuli i .e . small diameter fibre activation . Any stimulus that activates large fibres selectively would tend to decrease the transmission and the perception of other sensory messages . Conversely, specific activation of small fibres would tend to open the gate which might result in the experience of pain . If there is an ongoing sensation of pain, due to small fibre activity, then the selective activation of large fibres, e .g. by T .E .N .S ., light massage, gentle exercise etc ., may either decrease the pain or stop it completely . ENDORPHINS First discovered in 1975 by Hughes and Kosterlitz, (Terenius & Wahlstrom, 1978) the endorphins are endogenous morphine-like substances with a morphine-mimetic action in
  2. 2. the body . Endorphins are comprised of two main groups, the endorphins and the enkephalins . The difference between the two groups is based on the length of their amino acid chains the endorphins are the longer . The endorphins are dominantly found in the pituitary and the brain stem . Their action is probably that of a neuromodulator on higher centre activity . Their action is slow to onset but has a sustained effect on the central nervous sytem. (C .N .S .) The enkephalins are found in the spinal cord and are postulated to be neurotransmitters, quickly released and degraded (Terenius, 1978). Both the endorphins and the enkephalins are released in response to a noxious stimulus and at least one of their actions is to decrease the perception of pain . NON-OPIATE DESCENDING SUPPRESSION Another system that responds to a noxious "drive" on the C.N .S . is non-opiate in character (Watkins and Mayer, 1982). The system is activated by mid brain reticular formation activity as a result of ascending noxious stimuli. It acts through a descending, serotonin (5-Hydroxytriptamine) mediated system in the dorso-lateral funiculus of the spinal cord . It acts to inhibit the transmission of noxious stimuli to higher centres . SOCIAL AND PSYCHOLOGICAL FACTORS Apart from the physiological mechanisms, there are many other important factors which are capable of influencing pain perception, e.g . cultural back ground, past experiences of painful situations, attention, arousal, mood and expectancy (Fordyce, 1977 ; Frederickson et al, 1978). These factors will influence the perception of pain and the patient's expression of pain . Pain thresholds are remarkably constant across populations, yet between individuals the experience, and expression of pain varies considerably, depending on the prevailing emotional and mental state, and the responses of those around him. Not only does the experience of pain vary from individual to individual but it also varies within the individual from hour to hour depending on his emotional, physical and mental state at the time . Therefore, when preparing to use T.E .N .S ., the physiotherapist must take into account the physiological and psychological mechanisms involved and alter the treatment accordingly for the best results. THE T.E.N.S. MACHINE Many different models with widely varying specifications are available . A typical machine (Figure 1) will have two intensity controls to alter the delivered current from the output sockets. The delivered current should have a range between 0 to 100 milliamps. Most machines are powered by rechargeable batteries but a few are still designed for mains use. 2 Figure 1 : A T.E .N .S. machine. Intensity Control O Output O Pulse Width Frequency range can be from 1 to 1000 Hz ., but a desirable range would be from 5 to 200 Hz . High Frequency (H .F .) T.E .N .S . is taken to be from 50 to 200 Hz . with an optimum frequency around 100 Hz . Low Frequency (L .F .) is from 5 to 50Hz . with an optimal frequency around 10 Hz . Some machines also have variable pulse widths . There is still controversy over which pulse width to use. However, on physiological parameters alone it can be deduced that narrow pulse widths will stimulate large fibres before small an important prerequisite for activation of a neural gating mechanism (Howson, 1978) . Wide pulses will stimulate both large and small fibres and, by producing more intense sensory stimuli, may be more important in producing a "drive" on brain stem pain suppres. sion centres. Also included with the machine should be electrodes leads, contact gel and some means of attaching the electrodes to the patient. The manufacturer's supply is usually effective but expensive to replace . A less expensive means of electrode attachment is to use micropore or some other similar non. reactive adhesive tape . Precautions and Contraindications Few complications have been reported with the use ol T.E .N .S . The most commonly reported adverse reaction is skir irritation which can either be from current reaction, the contact medium or the adhesive tape . Care must be taken to examine the stimulation sites from time to time especially it patients who may leave the electrodes in place for a long time as with a chronic pain patient. T .E .N .S . may be used to mask pain in acute conditions such as sports injuries, but this is cautioned against as the risi of further damage to underlying structures is increased due to the withdrawal of the protective function of pain . T.E .N .S . should not be used :(a) at, or close to, a cardiac pacemaker. (b) over the carotid sinus. (c) in pregnancy, especially in the first trimester (Bishop, 1980 ; Lampe, 1978) Indications for Use Pain is virtually the sole indication for the use o1 T.E .N .S . It has been used effectively with acute pain, such a; post surgery, (Ali et al, 1981), and in many chronic condition; where pain is one of the dominant symptoms e.g . low back pain, cervical spondylosis, O.A . joints, tennis elbow etc (Paxton, 1980). The Journal of The Hong Kong Physiotherapy Associatia
  3. 3. Electrode Placement At least two electrodes are used in the application of each treatment . Contact is made using a liberal amount of contact gel . The electrodes are held securely on the chosen sites . Various placement strategies can be used (Mannheimer, 1978) . " LOCAL POINTS Placement of electrodes around, or close to, the point that is painful, as in lateral shoulder pain (Figure 2) . Figure 3 : Electrode placement for stimulation of the left sciatic nerve in a case of sciatica. " NERVE TRUNKS Along, or close to, the nerve trunk that supplies the painful area . In a left sided sciatica two points are chosen, one over the origin of the sacral plexus and the other distally over the nerve trunk (Figure 3) . " TRIGGER POINTS "These are spontaneously tender spots (Reynolds, 1981), usually found in a muscle belly . Some common trigger points are in the upper fibres of trapezius, the external occipital protruberence and in Temporalis . Usually bilateral electrode placement is employed in such cases (Figure 4) . " DERMATOMES Placement of one, or both, electrodes within the appropriate dermatome over the painful area . ACUPUNCTURE POINTS Much of the development of modern pain theory deserves its impetus for research to the emergence of acupuncture as a legitimate treatment modality in the West . The choice of the appropriate acupuncture point for T .E .N .S . can be a bewildering process. However, armed with an accurate diagnosis, a good knowledge of anatomy and an acupuncture chart, the intelligent physiotherapist should be able to work out which points to use . " POST - SURGERY Electrodes can be placed at either end of the incision line (Figure 5), on un-operated skin, as with a thoracotomy incision . This has been found not only to decrease pain, but also to increase respiratory function (Ali et al, 1981). Dosage (Table 1) With High Frequency T.E .N.S . the current intensity should never go beyond the comfort level i .e . low intensity . This will presumably activate large fibres and "close the gate" in the dorsal horn . The effect of H.F .T .E .N .S. appears quickly after the onset of stimulation but also disappears rapidly after the cessation of the stimulation . This would indicate that a neural mechanism is active . H .F .T .E .N .S . is used most often to modulate acute pain . Figure 2 : Electrode placement for lateral shoulder pain . Votume S, 1983. With Low Frequency T .E .N .S ., higher intensities must be used to "drive" brain stem centres to release the neurochemicals to modulate pain . Intensities should be strong, but not unbearable, possibly inducing a mild muscle contraction . L .F .T .E .N .S . has a longer latency period, from ten to fifteen minutes, but its effect outlasts the stimulation period from minutes to hours, or days in some cases . The time delay of onset and extended period of effectiveness implicates a neurohumoral mode of action for L .F.T .E .N .S . This method of stimulation is more often used in chronic pain syndormes . Treatment When treating acute pain, high frequency should be used, bearing in mind that current intensities will have to be raised during treatment as the receptors adapt to the stimulus . When using L.F .T .E .N .S . it is often advisable to precede it by the use of H .F .T .E .N .S . to institute a pain blocking mechanism . This would enable higher intensities to be used subsequently with L.F .T .E .N .S . with a resultantly more effective treatment . The use of H .F .T.E .N.S . is always advisable when treating the patient for the first time in order that the patient Figure 4 : Electrode placement for stimulation of trigger points .
  4. 4. may get some indication of the effectiveness of the treatment to block or modulate the pain without-any discomfort . If L.F .T .E .N .S . is desirable as with a chronic pain patient, this could be instituted gradually at a second or subsequent visit . The patient must have confidence in the machine and in the therapist for maximum treatment effectiveness . The therapist must therefore demonstrate confidence in the technique. The patient should learn as quickly as possible that he, or she, has control over his own pain . Different electrode placements can be tried until the most comfortable, but effective, position is found for that patient . PATIENT MANAGEMENT Essentially, T.E .N .S . is a user's machine . It is for the patient to have and use wherever necessary . Its function is to give to the patient an active and positive means to control the pain . The unit is small enough to be clipped on to the patient's belt and, with the electrodes in place, the patient needs only to turn on the machine when he feels it necessary . This is usually before it reaches unbearable levels . As the patient achieves control of his pain his activity level will increase . This will have positive psychological and physiological effects. The increase in active movement will increase large fibre stimulation which will in turn, further decrease the pain . His increased activity levels will lead to positive reinforcement from his surroundings which will give him renewed confidence . T.E .N .S . rarely stands on its own as a treatment modality but plays an important part in the overall management of the pain patient. It must be integrated with other forms of patient care, e .g . physical, pharmacological and psychological for complete treatment effectiveness. Table I : Suggested dosage for different "types" of pain . FREQUENCY STAGE ACUTE DOSAGE H .F . Daily x 3 - 20 mins SUBACUTE H .F . and L.F . Daily x 1 - 30 mins CHRONIC H.F . and L.F . P.R .N . - as required References Ali, J., Yaffe, C.S . and Serrette, C. The effect of transcutaneous electrical nerve stimulation on postoperative pain and pulmonary function . Surgery 89 : 507-12, 1981 . Bishop, B., Pain : Its physiology and rationale for management . Physical Therapy 60 : 13-27, 1980 . Fordyce, W. E., Learning processes in pain . In : Sternbach, R. (Ed.) . The psychology of pain, Raven Press, New York 49-72, 1978 . Frederickson, L.W., Lynd, R.S . and Ross, J., Methodology in the measurement of pain . Behaviour Therapy 9 : 486-488, 1978 . Howson, D.C ., Peripheral neural excitability - implications for T.E .N .S . Physical Therapy 60 : 38-44, 1980 . Lampe, G.N ., An introduction to the use of T.E .N.S. devices. Physical Therapy 60 : 13-27, 1980 . Mannheimer, J.S ., Electrode placements for T.E.N .S . Physical Therapy Melzack, R. and Wall, P., Pain mechanisms. A new theory Science 58 : 1455-1462, 1980 . 150 : 971-79, 1965 . Merskey, H., Pain and personality . In : Sternbach, R. (Ed.), psychology of pain, Raven Press, New York, 111-127, 1978 . CONCLUSION Transcutaneous Electrical Nerve Stimulation has been shown to be effective in the control of acute and chronic pain . Its effectiveness depends on the correct technical application of the machine, an adequate knowledge of the principles behind its application and a positive receptive attitude on the part of the patient. It provides the patient, especially the patient with chronic pain, with a tool to control the pain himself, often after many other modalities have been ineffective . Figure 5 : Electrode placement for the stimulus of a recent incision . The Paxton, S.L., Clinical uses of T.E .N .S.: A survey of physical therapists. Physical Therapy 60 : 38-44, 1980 . Reynolds, M.D ., Myofascial trigger point syndromes - an Approach to management . Archives of Physical Medecine and Rehabilitation . 62 : 107-110, 1981 . Solomon, R.A., Viernstein, M.C . and Long, D.M ., Reduction of postoperative pain and narcotic use by transcutaneous electrical nerve stimulation. Surgery 87 : 142-6, 1980 . Sternbach, R., Clinical aspects of pain . In : Sternbach, R. (Ed.), psychology of pain, Raven Press, New York . 293-299, 1978 . The Taylor, P., Hallet, M. and Flaherty, L., Treatment of osteoarthitis of the knee with transcutaneous electrical nerve stimulation. Pain 11 233-240, 1981 . Terenius, L., The endorphins : a history. Psychopharmacology 18 : 321-332, 1978. Advances in Biochemical Terenius, L. and Wahlstrom, A., The amino-acid structure of the enkephalins. In : Hughes, J. (Ed.) Centrally acting peptides. University Park Press, Baltimore. 161-178, 1978 . Wolf, L., Gersh, M. and Kutner, M., Relationship of selected clinical variables to current delivered during transcutaneous electrical nerve stimulation. Physical Therapy 58 : 1482-90, 1978 . Watkins, L. and Mayer, D., Organization of endogenous opiate and nonopiate pain control systems. Science 216 : 1185-1191, 1982 . 4 The Journal of The Hong Kong Physiotherapy Association