The objective is to reduce the level of pain experienced
in labour whilst invoking minimal risk for the mother and baby. The
level of pain experienced in labour varies widely with each mother. Some
women experience very little pain whilst others suffer from abdominal
and back pain of increasing intensity throughout their labours. Pain
relief must be tailored to the needs of the individual. Often a
combination of methods will provide the best results. The only technique
that can provide complete pain relief is epidural analgesia.
These agents are commonly reserved for use in the late
first stage and in the second stage. The most widely used agent is
Entonox, which is a 50/50 mixture of nitrous oxide and oxygen. The gas
can be self-administered and is inhaled as soon as the contraction
starts. Entonox is used in the UK by about 75% of mothers in labour and
is effective in about 40%. Other inhalation agents include
trichloroethylene 0.3?0.5%, and methoxyflurane 0.35%, in air. These
compounds take longer to achieve adequate analgesic concentrations
because they have a high degree of solubility in body fat. They are
effective in only 10% of women and their use has now been largely
abandoned.
Nitrous oxide has been shown to have adverse effects on
birth attendants if exposure is prolonged; these effects include
decreased fertility, bone marrow changes and neurological changes.
Forced air change every 6?10 hours is effective in reducing the nitrous
oxide levels and should be mandatory in all delivery rooms.
A A variety of narcotic agents have been used for pain
relief in labour and such agents are still widely used. Pethidine is the
most widely used narcotic agent and is given in doses of 50?150 mg
intramuscularly; the effects last about 2?3 hours, after which time the
dose can be repeated.
Current evidence suggests that pethidine has a weak
analgesic action but tends to reduce anxiety and discomfort. The
unwanted side effects include nausea, vomiting and respiratory
depression in both the mother and the baby. The effect on the neonate is
particularly important when the drug is given within 2 hours of
delivery. Pethidine is often administered with phenothiazines to reduce
nausea.
Other opioids occasionally used in labour include
papaveretum 10?20 mg, diamorphine 5?10 mg, pentazocine 30?60 mg,
phenazocine 1?2 mg or oxymorphone 1?1.5 mg by intramuscular injection.
The use of all these compounds, with the possible exception of pethidine,
is becoming increasingly uncommon as the use of epidural analgesia
increases.
The search for more effective agents continues and a new
agent, remifentanil, has recently been evaluated. This is an
ultra-short-acting opioid that produces superior analgesia to pethidine
and has less effect on neonatal respiration.
Because some mothers are unsuitable for regional
analgesia, opiates are likely to continue to play a significant role in
pain relief in labour .
Non-Pharmocological Methods
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Transcutaneous electrical nerve stimulation (TENS) involves the placement of two pairs of TENS electrodes on the back on each side of the vertebral column at the levels of T10?L1 and S2?S4. This can be effective in early labour but is often inadequate by
itself in late labour. For the technique to be effective, antenatal training of the mother is essential.
Other non-invasive methods include massage and relaxation techniques.
This is the most effective way of relieving the pain of contractions, with complete relief of pain in 95% of labouring women. The procedure may be instituted at any time and does not interfere with uterine contractility. It may reduce
the desire to bear down in the second stage of labour.
A fine catheter is introduced into the lumbar epidural space and a local anaesthetic agent such as bupivacaine is injected (Figure
1.). The addition of an opioid to
the local anaesthetic greatly reduces the dose requirement of bupivacaine, thus sparing the motor fibres to the lower limbs and reducing the classic complications of hypotension and abnormal fetal heart rate. The procedure involves:
- Insertion of an intravenous cannula and preloading with no more than 500 ml of saline or Hartmann?s solution
- Insertion of the epidural cannula at the L3?L4 interspace and injection of the local anaesthetic agent at the minimum dose required for effective pain relief.
Figure 1. Epidural Anaesthesia.
