The ‘gate control’ theory of pain suggests that stimulation of larger peripheral nerve fibres inhibits pain signals entering the central pain pathway, reducing the perception of pain – TENS provides this stimulation. Additionally, it is believed that the electrical stimulation also activates the release of the body’s own endorphins.

TENS is available as a handheld battery operated unit. Electrodes are placed onto the skin over specific spinal nerves. The electrodes need to be the correct size to stimulate the nerve fibres at the correct rate and density (Coates 1998). A water-based electrode gel is required to facilitate the current. Tape is used to keep the electrodes securely in the correct place if self-adhesive electrodes are unavailable.

TENS machines are adjusted according to the pulse frequency (the number per second), pulse duration and amplitude (strength of the current). The constant background tingling closes the gate on the pain and promotes endorphin production. With the boost facility the duration, amplitude and frequency are all increased, enhancing the pain relieving action yet further. The woman experiences the sensation as tingling on the skin; this should be through both electrodes and be at a comfortable level. If supplied with indicator lights, these are seen to flash intermittently, or to remain on continuously, according to the frequency. TENS should not be used in water, it may interfere with a cardiac pacemaker, damaged or sore skin should be avoided and it should not be used in the first trimester (Poole 2007a) or on the abdomen at any stage of pregnancy.

Studies conflict when considering the effect of TENS, so much so that NICE (2007) state that TENS should not be offered to women in established labour. However, levels of consumer satisfaction are good (Carroll et al 1997). As a non-pharmacological analgesic it has no known ill effects for the mother (so long as it is used according to the manufacturer’s instructions) or fetus. It allows the woman to mobilise, to utilise other analgesics as well and to have some control – aiding both her physiological and psychological equilibrium. Application in early labour is indicated to promote an increase in the woman’s natural endorphin level. Poole (2007b)

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