Re. Nancy Sherwoods request for information:  Transcutaneous Electrical Nerve
Stimulation is a very clever system using some small battery powered electrodes.
It works on the "gate theory " that only a certain number of impulses can be
processed at any time by the brain. Those impulses travelling superficial routes
i.e. skin stimulation arrive first and block the complete processing of the
deeper impulses i.e. uterine pain.
  Tens also encourages the body to produce its own natural painkillers -
endorphins. It is thought that epidurals reduce endorphins.
  Tens electrodes are attached to a mother's back, and feel like an electrical
massage. It works brilliantly for some, but its not everyones cup of tea.It
may be used for many different conditions besides labour. It offers considerable
pain relief, reduction in drug intake, and increase in control and activity
for a labouring mother. Inexpensive models are available.
                                               Mary Grant, RM, IBCLC.