Treatment - TENS

Question 1

What is TENS?

Answer 1

> Transcutaneous Electrical Nerve Stimulation

• low frequency electrical currents are applied to skin (biphasic nature of pulse means there’s no electrolyte build up - minimises skin reaction)
• aim is create pain relief by stimulating sensory nerves

*If motor nerves = triggered then it becomes muscle stimulation rather than TENS

Question 2

Compare with other treatments:

Answer 2

> Positive

• non-invasive
• minimal side-effects
• patient controlled
• portable (battery operated)

> Negative

• allergic skin reactions
• only SHORT TERM pain relief
• not better than other treatments for pain

Question 3

How does TENS work>

Answer 3

> Pain gate theory
- requires frequency of ~80-130Hz (patient dependent)
- triggers A beta fibres (mechanoreceptors - low threshold + myelinated)
- reduces transmission of C fibres
Endogenous opioid system
- a delta fibres are triggered
- frequency of ~ 2-10Hz (patient dependent - have a play + use ‘sweep’ setting - slower build in pulse)
- Signals from cortex/hypothalamus/amygdala trigger periaqueductal grey (midbrain)
- dorsolateral peri-aqueductal grey triggers locus coeruleus (pons) to release noradrenaline (mechanical noxious stimuli)
- ventrolateral peri-aqueductal grey triggers nucleus raphe magnus (reticular formation - medulla) to release serotonin (thermal nociception)
- This excite the interneuron at dorsal horn of spinal cord to release enkephalin = endogenous opioid - prevents transmission of pain signals up spinothalamic tract (inhibits substance P)
*By using burst mode we may be able to trigger both systems

Question 4

Procedure

Answer 4

> Always test skin sensation 1st - sharp/blunt + hot/cold
Check equipment
Informed consent + contraindications/hazards

> Vary (slowly)

• Intensity = strength
• frequency - how often
• width - length of pulse
• Down to patient preference (good starting point is ~80-100Hz on sweep setting ie longer waves)

> Modes

• Burst - high frequency is interrupted with ‘burst’ at rate if 2-3 per second (triggers both fibres + both pain mechanisms)
• modulation (less regular) - prevents brain getting used to stimuli = ‘accommodation’

> Placement of electrodes

• stimulate nerves entering spinal cord at same levels as pain
• Cover painful area

Question 5

Types of TENS

Answer 5

> Normal

• high frequency + narrow pulse width
• not uncomfortable but definite feeling
• at least 30 mins (however long is needed)
• SHORT TERM PAIN RELIEF (limited carry over)
• acute pains - triggers mostly A beta fibres

> Acupuncture TENS

• low frequency + wide pulse width
• strong intensity (not quite at pain threshold)
• > 30 mins (intervals throughout day)
• Carry over = few hours
• Chronic pain - A delta fibres = triggered#

> Brief Intense TENS

• high frequency + wide width
• Intensity is close to pain threshold
• 15-30 mins treatment
• Immediate pain relief

Question 6

Contraindications

Answer 6

> Cognitive difficulties
Pregnancy
- on trunk/pelvis for 1st 12 weeks
- over uterus - at any stage
- can mess with foetal monitoring if used during labour
over growth plates in children
over anterior of neck (reduce circulation to brain)
Pacemaker (mess with frequency)
Skin conditions - allergies/infection/eczema/devitalised
abnormal sensation - test 1st
Compromised circulation
Active cancer/Tb - may stimulate cells
Epilepsy - may trigger seizure (consult doc 1st)

Question 7

Hazards

Answer 7

> Drop in blood pressure 
> Skin irritation/burns 
> Electric shock (keep electrodes apart)
*Advise never to use in pool/shower or while operating heavy machinery 
*Document this in INFORMED CONSENT