Electrical Nerve Stimulation Through the Skin (TENS)
TENS is a low-frequency current used for therapeutic purposes. Stimulation devices that send electric current through the intact surface of the skin are considered TENS. There are several types of TENS, including Conventional TENS, Acupuncture TENS, Brief Intense TENS, and Burst TENS (AGNE, 2004).
Conventional TENS
Conventional TENS selectively activates the AB filaments without activating the pain-related filaments: C and A8. Through experiences, it is believed that conventional TENS produces segmental anesthesia, with rapid onset and termination, localized in the dermatome. Users report feeling comfortable paresthesia below the electrodes.
During conventional TENS, currents are usually sent with frequencies between 10 and 200 p.p.s, with a duration of 100-200 microseconds, and pulse amplitude dosed to produce strong paresthesia. The pulse manifestation is generally continuous, although conventional TENS can be sent in “bursts” or “trains”. This fact has been described by some authors as Burst TENS (HOWE and TREVOR, 2003).
Acupuncture TENS
Defined as the induction of phasic muscle contractions, which are not painful, in the myotomes related to the site of pain. The purpose is to selectively activate the small-diameter filaments originating in the muscles (ergoreceptors) through the induction of phasic muscle twitches. Therefore, acupuncture TENS is performed on the motor points of the efferent filaments Ac, creating a silent muscle twitch that results in the activity of the ergoreceptors.
Evidence suggests that acupuncture TENS creates extrasegmental anesthesia in a similar way to that suggested for acupuncture (HOWE and TREVOR, 2003).
Brief Intense TENS
The purpose of brief intense TENS is to activate cutaneous efferents by emitting the current over the peripheral nerves originating from the site of pain at an intensity that is just tolerable for the patient. Transcutaneous electrical nerve stimulation is performed on the site of pain or the main nerve bundle where the pain originates. Tolerable intensities are used for the patient. Since it is an uncomfortable current, it can be emitted for a short period of time.
It has been shown that the activity in cutaneous efferents, induced by brief intense TENS, produces peripheral blockade of nociceptive efferent activity and segmental and extrasegmental anesthesia (HOWE and TREVOR, 2003).
Variable Intensity Frequency (VIF) TENS
TENS current that varies in intensity and frequency. The irregularity increases therapeutic efficacy, avoiding accommodation, producing an excitomotor effect and an antalgic vibration (AGNE, 2004; TRIBIOLI, 2003).
Burst TENS
The base frequency of Burst TENS is 100Hz and the bursts (repetitions of pulses in a certain time) are fixed at 2Hz (AGNE, 2004).
Physiological Effects
The physiological effects of TENS can be subdivided into analgesic and non-analgesic effects. The analgesic effects are used for symptomatic pain relief. The non-analgesic effects are used for restoring blood flow to ischemic tissues and wounds, although there is a lack of publications on this topic (JOHNSON, 2003).
Contraindications
According to Frampton (1998), TENS is a safe method. In general, contraindications are based on common sense and are mentioned to avoid possible litigation.
Do not use TENS in people who:
Use pacemakers.
Have heart disease or arrhythmias.
Have undiagnosed pain.
Have epilepsy and do not have proper medical attention and advice.
Are in the first trimester of pregnancy.
Do not use TENS in the following areas of the body:
Mouth.
Carotid sinus.
Anesthetized or altered sensitivity skin.
Abdomen during pregnancy.
Near the eyeball.
Precautions:
The basic safety principles, according to Frampton (1998), are:
Keep electrodes and application instruments out of the reach of children.
Do not use TENS while driving or when using potentially dangerous equipment.
Unplug the device before applying and removing the electrodes.
Adverse reactions
The waveform of TENS does not cause polar effects, so it does not cause adverse dermatological reactions (AGNE, 2004). Patients may experience skin irritation or welts below or around the electrodes. This is due to dermatitis at the contact site with the electrodes due to constituents of the coupling gel or adhesive tape (FRAMPTON, 1998).
Indications
TENS is mainly used for the symptomatic management of acute and chronic pain of benign origin. TENS is applied through pulsed currents sent through the intact surface of Translation:
