Spinal
With an epidural, the epidural needle is inserted only as far as the epidural space. This is a 4mm space located just outside a layer of tissue called the 'dura mater'. The dura mater tissue encases the spinal cord and spinal fluid.
Once the needle is believed to be in the correct location, a fine tube (about the width of fishing line) is passed through the hollow needle, so that the end of the tube rests in the epidural space, then the epidural needle is removed. The tube is about 90cm long and the remainder of the tube is eventually taped in place, up the length of the woman's back.
The anaesthetic medication(s) chosen by the anaesthetist are then injected down the tube (or catheter) to 'bathe' the nerves that lead to the woman's uterus and lower body to numb them.
The epidural medications take about 10 to 20 minutes to relieve the pain and last for 1 to 2 hours.
Once the initial dose of medication has worn off, the epidural can be 'topped up' with more medication being administered down the epidural catheter. This will most likely occur if the labour is still continuing or the woman needs to have a
forceps,
ventouse or Caesarean birth. You may wish to read more in
epidurals for labour.
Spinal
With a spinal anaesthetic, instead of the fine, hollow, spinal needle being inserted as far as the epidural space, it is pushed in a little further to actually pierce the 'dura mater' layer of tissue (the dura mater being the tissue that encases the spinal cord and spinal fluid). The end of the needle reaches the cerebral spinal fluid, or 'CSF' (the pool of fluid that surrounds the spinal cord and flows around the brain). The initial procedure is similar to a
spinal tap, except that the spinal fluid is not removed.
Once the needle is in place, the anaesthetist injects the chosen (often combination) of medications into the spinal fluid, bathing the nerves of the spinal cord that lead to the woman's lower body.