Pain Control With Transcutaneous Electrical Nerve Stimulation
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.
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.
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
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 .
First discovered in 1975 by Hughes and Kosterlitz,
(Terenius & Wahlstrom, 1978) the endorphins are endogenous
morphine-like substances with a morphine-mimetic action in
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
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
Figure 1 : A T.E .N .S. machine.
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.
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
The Journal of The Hong Kong Physiotherapy Associatia
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,
" 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) .
Placement of one, or both, electrodes within the appropriate
dermatome over the painful area .
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 .
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
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 .
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 .
H .F .
Daily x 3 - 20 mins
H .F .
and L.F .
Daily x 1 - 30 mins
and L.F .
P.R .N . - as required
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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
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The Journal of The Hong Kong Physiotherapy Association