SAFETY MEASURES:
TENS electrodes should never be placed:
Over the eyes due to the risk of increasing intraocular pressure[23]
Transcerebrally[24]
On the front of the neck due to the risk of a acute hypotension (through a vasovagal reflex) or even a laryngospasm[23][25]
Through the chest using an anterior and posterior electrode positions,[23] or other transthoracic applications understood as “across a thoracic diameter”; this does not preclude coplanar applications[25]
Internally, except for specific applications of dental, vaginal, and anal stimulation that employ specialized TENS units[23]
On broken skin areas or wounds, although it can be placed around wounds.[23]
Over a tumour/malignancy (based on in vitro experiments where electricity promotes cell growth)[23][25]
Directly over the spinal column
TENS should not be used across an artificial cardiac pacemaker (or other indwelling stimulator, including across its leads) due to risk of interference and failure of the implanted device. Serious accidents have been recorded in cases when this principle was not observed.[25] A 2009 review in this area suggests that eletrotherapy, including TENS, “are best avoided” in patients with pacemakers or implantable cardioverter-defibrillators (ICDs). They add that “there is no consensus and it may be possible to safely deliver these modalities in a proper setting with device and patient monitoring”, and recommend further research. The review found several reports of ICDs administering inappropriate treatment due to interference with TENS devices, but notes that the reports on pacemakers are mixed: some non-programmable pacemakers were inhibited by TENS, but others were unaffected or auto-reprogrammed.[26]
On areas of numb skin/decreased sensation TENS should be used with caution because it’s likely less effective due to nerve damage. It may also cause skin irritation due to the inability to feel currents until they are too high.[23] There’s an unknown level of risk when placing electrodes over an infection (possible spreading due to muscle contractions), but cross contamination with the electrodes themselves is of greater concern.[27] TENS should also be used with caution in people with epilepsy or pregnant women; do not use over area of the uterus as the effects of electrical stimulation over the developing fetus are not known.[25][28]
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