Contraindications to TENS are few and mostly hypothetical with few reported cases of adverse events associated with TENS in the literature. Nevertheless, therapists should be cautious when giving TENS to certain groups of patients:
Those suffering from epilepsy: If the patient were to experience a problem while using TENS, from a legal perspective it might be difficult to exclude TENS as a potential cause of the problem.
Women in the first trimester of pregnancy: TENS' effects on fetal development are as yet unknown (although there are no reports of it being detrimental). To reduce the risk of inducing labour, TENS should not be administered over a pregnant uterus although TENS is routinely administered on the back to relieve pain during labour.
Patients with cardiac pacemakers: This is because the electrical field generated by TENS could interfere with implanted electrical devices.
Rasmussen et al. (1988) reported that TENS did not interfere with pacemaker performance in 51 patients although TENS may induce artifacts in monitoring equipment (Hauptman and Raza, 1992; Sliwa and Marinko, 1996).
Chen et al. (1990) reported two cases of a Holter monitor detecting interference of a cardiac pacemaker by TENS and in both instances the sensitivity of the pacemaker was reprogrammed to resolve the problem. These authors suggest that careful evaluation and extended cardiac monitoring should be performed when using TENS with pacemakers. Therapists wishing to administer TENS to a patient with a cardiac pacemaker or any cardiac problem should always discuss the situation with a cardiologist.
TENS should not be applied internally (mouth), or over areas of broken or damaged skin.
Therapists should ensure that a patient has normal skin sensation prior to using TENS, because if TENS is applied to skin with diminished sensation the patient may be unaware that they are administering high-intensity currents and this may result in a minor electrical skin burn.
TENS should not be delivered over the anterior part of the neck as currents may stimulate the carotid sinus leading to an acute hypotensive response via a vasovagal reflex. TENS currents may also stimulate laryngeal nerves, leading to a laryngeal spasm.
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