Although labour is a physiological process many woman feel the need to resort to different methods of pain relief to help them cope with what can be the overwhelming pain of labour.
The exact defi nition of what constitutes a medical form of pain relief is open to debate. Most practitioners would take it to include all drugs, whether taken orally, by injection, by inhalation or by regional block. Other methods of pain relief are less easy to catego- rise. These include transcutaneous electronic nerve stimulation (TENS), acupuncture, aromatherapy and other alternative or com- plementary therapies. It may be argued that any form of pain relief, whether drug-related or not, that involves an invasive procedure is
‘medical’. However, a woman who is enabled to use her own choice of alternative therapy during labour will probably feel that she has laboured ‘naturally’ and without medical pain relief.
An analgesic can be defi ned as a drug which reduces the pain sensation but without causing a loss of consciousness or touch (Ndala 2005d). The most desirable characteristic of an analgesic given during labour is that it should provide maximum pain relief with minimal adverse effects on the woman and her baby. Unfortu- nately, as will be seen, the perfect labour analgesic is not currently available!
It is important, however, that the midwife remains up to date with the current methods of analgesia and is able to inform women of their potential benefi ts and side-effects. This information should be given in a clear, unbiased way during the antenatal period so that women and their families have time to consider their options.
Nitrous oxide/Entonox
Entonox is a colourless, odourless gas which consists of nitrous oxide and oxygen in equal parts. It is colloquially referred to as ‘gas
and air’ or sometimes ‘laughing gas’. It is approved for use by midwives and can be used throughout labour, although a woman inhaling it continually throughout a long labour may start to tire and be unable to use it effectively.
Entonox is provided by piped supply directly into the delivery room or stored in portable cylinders which may be carried by mid- wives and used in the home setting. The gases start to separate if stored at a temperature below −7 ºC. For this reason it is important that cylinders are stored at a temperature of at least 10 ºC and inverted several times before use in order to ensure that the gases are adequately mixed (Ndala 2005d).
Women inhale the gas by breathing it in via a mouthpiece or a face mask. As the analgesic effect of the gas does not take effect until after about 20 seconds, the woman should be encouraged to start inhaling as soon as she feels the contraction beginning. In this way, the maximum effect of the analgesic will coincide with the peak of the contraction.
The midwife can assist the woman by helping her to breathe the gas in effectively. It is suggested that taking short panting breaths is not effi cient and the woman should be encouraged to take deep breaths at the normal breathing rate (Bryant and Yerby 2004).
Rapid breathing should be discouraged as it can lead to hyperven- tilation and less oxygen getting to the baby via the placenta (Gamsu 1993).
A notable advantage of Entonox during labour is that it is excreted rapidly via the maternal lungs so that toxic levels do not accumulate and affect the fetus adversely. If a woman does not like the sensa- tions evoked by using the gas, she simply stops inhaling it and the effect is soon lost. Some women report feeling dizzy and nauseous while inhaling entonox, although the majority fi nd that the sense of euphoria evoked, coupled with the lessened pain sensation, make it a popular pain-relieving choice.
Entonox is not, however, the perfect analgesia for labour in that while it helps many women cope with the pain of the contractions it does not take away the pain sensations completely and in this sense is not a true analgesic (Bryant and Yerby 2004).
Epidural analgesia
Epidural analgesia involves the introduction of a local anaesthetic into the epidural space around the spinal cord. Drugs which have been used include opiates such as diamorphine, morphine and fen- tanyl. It has been found that mixing an opiate with a local anaes-
thetic gives longer, more effective pain relief with less loss of movement in the lower limbs (Collis et al. 1993). This is known as the ‘mobile epidural’ and it means that potentially women are able to walk about as their labour progresses. The initial study used an injection of the combined drugs straight into the cerebrospina fl uid via the subarachnoid space followed by an insertion of an epidural catheter. It was also known as a ‘combined spinal epidural’ (Collis et al. 1993). However, this method has largely been discontinued and anaesthetists tend to use the combined drugs directly into the epi- dural space (Eisenach 1999). The drugs commonly used are bupiva- caine (the local anaesthetic) and fentanyl (the opiate).
The epidural space (see Figure 5.4) is approximately 4 mm wide and located around the dura mater (the outermost layer of the meninges surrounding the spinal cord). It contains a number of
Spinal cord
Epidural space Lumbar 3
Lumbar 4
Figure 5.4 The epidural space
blood vessels, fatty matter and spinal nerves. During pregnancy and more specifi cally labour, the size of the space is reduced consider- ably by the engorgement of the veins which occur during preg- nancy. The local anaesthetic is inserted into the space with the aim of surrounding the fi bres of the spinal nerves in order to block the pain sensations. It is usual practice for the lumbar route to be used and usually the anaesthetic is introduced between the lumbar ver- tebrae 2 and 4 or 2 and 3.
An epidural may be indicated in the following situations:
• It is the woman’s choice as an effective method of pain relief
• During prolonged labour as this method is usually very effective and will allow an exhausted woman a chance to rest and recuperate
• A malposition such as occipital-posterior which often leads to severe back pain and an early need to push before the cervix is completely open
• A malpresentation such as a breech where certain manipulations are likely to be required during the second stage of labour and there is a higher risk that a caesarean section might be indicated
• Multiple pregnancy for reasons as above
• A woman who has very high blood pressure. The use of epidu- ral analgesia may lead to a reduction in blood pressure as the local anaesthetic blocks the transmission of both motor and sensory nerves as well as having an effect on the sympathetic nervous system. This will cause dilation of the veins and a sub- sequent fall in blood pressure
• Pre-term labour in order to avoid the use of narcotic drugs which will pass through the placenta and may have an adverse effect on the fetus
• For instrumental (forceps and ventouse (suction) deliveries and operative deliveries (caesarean section)
(Ndala 2005d).
On the other hand, an epidural is not recommended if a woman has chronic backache or a spinal deformity, as this could lead to diffi culties during the procedure. If she has a blood clotting disorder this might lead to excessive bleeding around the site where the needle is introduced into the spinal cord. Due to the effect which this type of anaesthesia has on blood pressure, it is not recom- mended if a woman has low blood pressure or a low blood volume (Ndala 2005d). In this situation, the woman would be advised to use another method of pain relief such as pethidine or diamorphine.