2022 TENS

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Transcutaneous Electrical
Nerve Stimulation

Scott D McPhee, DrPH, OTR/L, FAOTA
Alfred Bracciano, EdD, OTR/L, FAOTA

In order to prepare for the module on transcutaneous electrical nerve
stimulation, please read the corresponding chapter in Physical Agent
Modalities: Theory and Application for the Occupational Therapist, by Alfred
Bracciano.

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Learning Objectives

At the end of this module, you will:

1. define the therapeutic goals of electrical therapy.
2. identify the physiological events associated with electrical stimulation.
3. define the distinguishing characteristic and indications and

contraindications of electrical stimulation.
4. distinguish the physiological effects of various parameters of electrical

stimulation (voltage, type, dosage, duty cycle, etc.).
5. discuss the therapeutic relationship of electrotherapy with other

therapeutic procedures.
6. discuss appropriate patient education procedures for safe application of

transcutaneous electrical nerve stimulation.
7. discuss essential elements of documentation for transcutaneous electrical

nerve stimulation.

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Pain

Pain is a complex disorder that can affect an individual systemically,
psychologically, physiologically, emotionally and socially, and usually will result in
an unpleasant sensory and emotional experience associated with actual or
potential tissue damage.

Pain is also the most frequent reason for admission to an emergency room.

Although there are a number of theories which have been postulated to explain
how pain is commonly transmitted, research is still being conducted to further
understand the complexities of pain, especially in the area of neuropharmacology.

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Electrical Stimulation

During the 1960’s, it was hypothesized that stimulation of non-nociceptors or their
axons would interfere with the transmission of sensation from nociceptors to the
higher centers of the brain where pain is perceived. It was postulated that pain
could be modulated with electrical stimulation by affecting the perceptual
component that alters the symptom rather than the cause of the pain.

Thus, transcutaneous electrical nerve stimulation, generically called TENS, was
developed as a means to curb pain by applying low- voltage electrical pulses to the
nervous system that controls the perception and sensation of pain.

The two primary theories that address pain modulation associated with TENS and
electrotherapy are the Gate Theory and the Endorphin/Opiate-Mediated Control
Theory.

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Gate Control Theory

According to the Gate
Control Theory, when painful
stimuli is transmitted to the
brain and conveyed to the
spinal cord by small-
diameter, slow conducting
nociceptive nerve fibers with
minimal or no myelin (A-
delta, C), the painful stimuli
can be inhibited by the
activity of large-diameter fast-conducting, highly myelinated, proprioceptive
sensory A- beta fibers.

• The fast-conducting fibers can activate the substantia gelatinosa in the
spinal cord to block the transmission of impulses by the T cells and “gate”
the pain, which will subsequently lower its perception during stimulation.

However, electrical stimulation may also affect modulation of the pain
transmission at the spinal cord if it increases the activity of the A-beta fibers.
Furthermore, carryover of pain reduction following stimulation may be due to
the interruption of the pain-spasm-pain cycle, and an increase in the stimulation
of the A-beta fibers may be necessary during habituation of the pathways to
keep the gate closed to the pain stimulus.

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Endorphin/Opiate Mediated Theory

According to the Endorphin/Opiate-Mediated Theory, endorphins are released in
the body and can bind to specific receptor sites in the central and peripheral
nervous systems to decrease the perception of pain and nociceptive response.

• These endogenous opiates are the body’s natural pain relievers and are
produced by the pituitary gland and in the spinal cord.

However, electrical stimulation can also induce bodily production of the
endogenous opiates which will interact with the receptors that block the
perception of pain.
Furthermore, electrical stimulation will increase the levels of endorphins
circulating in the cerebrospinal fluid of patients with various neurological
disorders that can subsequently decrease the perception of pain.

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Acupuncture

Traditional Chinese medicine has provided a wealth of historical and anecdotal
evidence how acupuncture can relieve pain by stimulating specific areas of the
skin’s energy lines or meridians.
This technique is effective because basic acupuncture points are highly innervated
and vascularized regions of the body that are capable of overlying nerves at
superficial aspects.
Acupuncture points are also electrically active and commonly exhibit decreased
resistance to electrical current flow.

• These points can provide an “entry” along the meridians to treat a wide
variety of conditions or to decrease certain functions when incited with
electrical stimulation.

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Transcutaneous Electrical Nerve Stimulations

• 4 Types of Simulation
– Sub-sensory
– Sensory
– Motor
– Noxious

TENS is used to manage pain in a variety of musculoskeletal disorders, including
low back pain, arthritis inflammatory disorders of soft tissue, postoperative pain
and other disease processes.
Since there are several methods for administering TENS that will elicit different
neurophysiological responses, the treatment parameters may need to be varied to
adequately achieve the desired outcome for certain patients.
Treatment applications which incorporate electrical stimulation will consist of
either pulsed or alternating current and may involve different combinations of
stimulation patterns.
The four types of stimulation that are commonly used include the sub-sensory
level, sensory level, motor level, and the noxious level.

• However, it may be necessary to try more than one method or combination
of methods to achieve the most effective pain relief.

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Sub-Sensory Stimulation

• Known as MENS or subliminal stimulation

Sub-sensory level stimulation (known commercially as microcurrent electrical
neuromuscular stimulation (MENS) or subliminal stimulation), can deliver
monophasic pulsed current at intensities that are below the threshold for nerve
depolarization.

• The pain-relieving effect of this type of stimulation is thought to involve
mechanisms other than pain gating or endorphin release in which the
microamperage currents are effective at enhancing cellular physiology and
processes.

MENS can also generate currents consisting of moving ions in the biological tissues
that do not have sufficient strength or magnitude to produce a response in the
nerves or muscles which will cause cutaneous sensations.

The theory of how MENS reduces pain and aids in tissue repair is based on The
Principle of the Arndt-Schulz Law. The application of a subthreshold electrical
signal to produce a physiological response of restoring the normal course of
electric current flow that is thought to be disrupted in injured tissues. The
realignment of the normal electric current flow through body tissues is believed to
reduce pain and aid in faster tissue repair and recovery from injury.

Although there are anecdotal reports that support the efficacy of this form of
stimulation to reduce pain, controlled studies have failed to demonstrate the
treatment is significantly more effective than a placebo.

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Sensory Level Stimulation

Sensory-level stimulation
(also called conventional
TENS or “high rate” TENS)
is commonly used to
control pain during the
acute stages of an injury.
It has been hypothesized
that this type of stimulation operates under the same parameters as the gate
control mechanism and may also affect opiate-mediated pain control.
Basically, conventional TENS involves using amplitudes and durations that are
delivered between 50-100 pulses per second which activate the cutaneous tactile
sensory fibers and subsequently produce a cutaneous parethesias or tingling
sensation without eliciting any motor response.

• When the pulse duration is between the range of 20 to 100 micro seconds
and the current amplitude is increased to the highest setting, it will yield a
sensory response without causing any muscle contraction.

However, a decrease in the nociceptive response will be relatively quick and
generally will occur within five minutes after starting the stimulation.

• Long term effects will also be limited and a decrease in the sensation of
pain will usually not last longer than one hour after the stimulation has
been stopped.

• Finally, if there is any prolonged reduction in the pain, this may be due to
the interruption of the pain-spasm-pain cycle.

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Sensory Level Stimulation Settings

The frequency should be positioned between 50 to 200 pps (burst per second or
beats per second) so the setting will result in a tingling sensation that is not
painful to the patient and not strong enough to result in muscular fasciculations.

• The initial treatment should be no longer than one hour to evaluate the
patient’s response and determine the appropriate period of use
thereafter.

• Therefore, the treatment will be based both on the patient’s needs as well
as the length of the therapy (which may continue for several hours).

• Also, to achieve the most effective treatment, the electrodes should be
placed over or near the location of the reported pain.

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Motor Level Stimulation

• Strong low-rate or acupuncture like TENS

Motor-level stimulation (also called
strong low-rate (SLR) or
acupuncture-like TENS) is
characterized by high amplitude
and low frequency in which the
pulse duration is set between a
range of 100 to 300 microseconds.

• It is thought this type of pain
reduction may be due to the gate control theory or opiate-mediated pain
control.

• However, the amplitude needs to be high enough to produce visible muscle
contractions, although it may cause some discomfort to the patient.

Furthermore, smooth isometric or isotonic tetanic contractions can be elicited by
using higher amplitudes of stimulation due to the recruitment of additional
motor axons or muscle fibers.

• Conversely, if the stimulation frequency is too low, the tissue response can cause
either tremors or twitch-like contractions. Also, care should also be taken to
avoid any joint movement that may be contraindicated due to the muscle
contraction.

The electrodes, therefore, should be placed over the motor points which
correlate with the location of pain or placed on the segmental nerve roots
corresponding with the location of pain. The suggested uses for motor-level
TENS include the treatment of chronic pain, pain caused by damage to deep
tissues, myofascial pain, and pain caused by muscle spasm.

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Noxious Level Stimulation

• Known as electro-acupuncture, hyperstimulation, or noxious level TENS
–

Noxious-level stimulation, also known as electro-acupuncture, hyperstimulation,
or noxious-level TENS, may be used prior to passive stretching, debridement, or
minor surgery.

• Noxious-level stimulation is delivered by utilizing a motor-level intensity in which
the pulse frequency is greater than 100 pps, the pulse duration is between 300
and 1000 microseconds, and the treatment length is from a few seconds to a few
minutes.

• The noxious-level stimulation will subsequently be reached when the stimulation
amplitude is increased to a level that is perceived as painful by the patient.

• Basically, the intense stimulation will activate the ascending neural mechanisms
after they reach the brain and the impulse will cause the release of endogenous
opiates that will subsequently inhibit the release of substance P, a
neurotransmitter of noxious impulses.

Pain reduction will occur because of the activating mechanisms in the brain stem
that dampen or amplify pain impulses, and pain relief can be obtained due to the
formation of a
negative feedback
loop within the
central nervous
system. Although
high levels of
analgesia can be
achieved with this
protocol, the effects may be short-lived and transitory.

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Electrode Placement

Most TENS units have four
electrodes in which two originate
from each of the two channels.

• When two or more channels
are necessary,
consideration should be
given regarding the
placement of each
electrode in relationship to
the other possible
placements.

• Clinicians should also test
different electrode configurations to determine which one will be most
effective to treat the problem area and meet the patient’s goals.

As a rule of thumb, the first choice should be to position the electrodes over or
around the painful site.

• Other considerations should include identifying the motor points, trigger
points, and acupuncture points that are electrically active since they can
facilitate the current flow into the selected tissue.

However, it should be noted that all three are resistant to palpation and can be
painful or tender with referred pain.

Therapists need to identify whether the desired outcome will involve a motor
response, sensory analgesia, or noxious stimulation for analgesia.

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Stimulation Sites

The stimulation sites include superficial points along the peripheral nerves, tissue
overlying painful areas, specific dermatomes or spinal segmental myotomes,
trigger points, motor points, and acupuncture points.

• The electrodes can be placed either parallel to the painful site, on either
side of a scar or surgical incision, crossed at the site of localized pain,
bracketed, or linear.

• E electrode patterns can be unilateral, bilateral, or contra-lateral.
When monitoring the patient’s response, the initial electrode placements should
be changed if the treatment outcome is less than expected or if the patient is
experiencing pain or discomfort.

• The effect of TENS can be maximized if the nerve (or nerves) involved in the
transmission of the pain can also be stimulated.

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Dermatomes

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Contraindications

Although TENS is safe and effective, the
technology is contraindicated for certain
diagnoses and body areas.

• TENS units should not be used with
demand-type cardiac pacemakers
because they may interfere with their
function and performance.

• TENS should not be used during labor and delivery nor performed on the
trunk or abdomen of pregnant women.

• TENS should not be applied directly over the eyes of individuals with epilepsy
or malignancies, nor
given to patients
who have a
peripheral vascular
disease or infection,
decreased or absent
sensation, or
undiagnosed pain.

• Electrodes should
not be placed over
the carotid sinus
area or trans-cerebrally.

• Since TENS may suppress the sensation of pain, care should also be taken for
patients who are experiencing acute pain as the protective mechanism that
indicates potential tissue damage may be affected.

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Clinical Reasoning Process

TENS can be used as part of an overall treatment process and is an effective
adjunct or alternative to pharmacological or surgical interventions when used to
modulate pain.
Before using TENS, therapists should first complete a thorough evaluation to
ensure the intervention is appropriate for the condition.

• As part of the clinical reasoning process, consideration should be given to
the type of pain, length of healing, and the psychological reaction and
behavior to the pain.

• Clinicians should also administer a pain scale using consistent
administration and scoring to assist in determining the efficacy of the
intervention and to identify any changes that may be necessary.

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If the patient has had any chronic, generalized pain that is poorly localized and is
related to an injury that had occurred several months prior to the evaluation, a
positive outcome for pain modulation is usually unlikely.
Prior to the resumption of any occupational activities, a review of the patient’s
occupational performance should also be completed since it may impact the
pain modulation.
Finally, to help expedite the outcome, the patient should understand how the
treatment and role of TENS will affect the injury and healing process.

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Application

The variables that can be adjusted to deliver the appropriate amount of
stimulation include the pulse rate, pulse width, and the intensity.

• Although there is no universal agreement as to the optimal TENS mode
or electrode placement for a given diagnosis or pathology, many
patients have indicated they prefer low-amplitude conventional TENS
and lower-amplitude formats of other modes such as brief intense,
pulse-burst, or modulation.

• Therefore, as a starting point, clinicians should use the conventional
mode TENS or preset the duration at a low point and the frequency at a
high point.

Electrodes should also be bracketed around the area of pain or on the localized
region of the pain, and the amplitude should be increased until the patient
reports a tingling sensation associated with parethesias.

• The frequency should be set between 50 and 80 pps, the pulse duration
should be between 50 and 100 milliseconds, and the treatment duration
should be between 20 and 60 minutes.

• Patients, though, should be monitored throughout the course of the
treatment and adjustments of the stimulation characteristics may be
necessary to achieve the desired effects.

• Also, if there is no muscle response, it should be noted.
The treatment should be discontinued if the patient shows any signs of distress or
cannot tolerate the stimulation input.

• When the patient is unable to tolerate the stimulation or the level of pain
does not decrease, the electrode location should be changed and the
stimulation parameters should be readjusted.

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• If the patient continues to report discomfort, a different form of TENS
should be considered such as acupuncture-like TENS, brief intense TENS,
burst mode TENS, or hyper-stimulation TENS.

However, if the patient is able to tolerate the sensation, reports a decrease in
pain and indicates there is an improvement of functional movements, the
stimulation should be continued.

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Alternate Forms

Acupuncture-like or strong, low-rate TENS can be used to provide pain
modulation during a chronic phase of pain.

• The amplitude setting should be strong, yet still provide a comfortable
rhythmic muscle twitch during a treatment period of 30 to 40 minutes.

• Brief intense TENS may also be used for short-term pain relief and can be
effective prior to a painful procedure such as joint mobilization, passive
stretch, friction massage, or wound debridement.

However, the amplitude should be set to the patient’s tolerance level and the
treatment duration should be no longer than 15 minutes.

Burst mode or pulse trains TENS can provide both high and low-rate TENS
characteristics, the treatment is easily tolerated by patients, and it is usually long
lasting.

• To achieve a tingling sensation or paresthesia, the amplitude should be set
at a frequency between 50 and 100 pps and cycled in bursts of 1 to 4 pps
during a treatment period between 20 and 30 minutes.

Additionally, point stimulation or hyperstimulation TENS is used to locate and
stimulate acupuncture or trigger points.

• However, it may be necessary to stimulate multiple sites so that a noxious
level can be achieved.

The amplitude is normally set at the patient’s tolerance level and the frequency is
set between 14 and 30 seconds at each point.

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Assessment

Patients should be re-evaluated after the treatment session to determine if there
are any significant changes in the pain levels and occupational performance.

• Visual or analog pain scales can also assist in tracking the changes and
provide the length of the pain modulation.

Since patients frequently use TENS units in their homes, they should be given
verbal and written instructions and queried whether they understand the
precautions, contraindications, and the electrode preparation and placement.

• The critical information should also be highlighted in the written
instructions to ensure the units are operated safely and properly.

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Documentation

The TENS documentation should include the treatment parameters, electrode
placements, pain scales and drawings, and patient compliance.

• Additionally, subjective indications of sensation and changes in the patient’s
condition during and after the stimulation should be recorded.

• Furthermore, the type of electrical stimulation, mode of delivery, pulse
duration, frequency, intensity, and duration of treatment should be in the
patient’s record.

• If there are changes in occupational performance and functions, any
improved tolerance or engagement of an activity or range of motion, they
should also be documented.