Pain Relief in Labour Clinical Trial
Official title:
A Randomised Controlled Trial of Remifentanil Intravenous Patient Controlled Analgesia (PCA) Versus Intramuscular Pethidine for Pain Relief in Labour
Childbirth can be an extremely painful and the provision of pain relief during labour is a vital component of a positive maternal experience. The majority of women who deliver in modern obstetric units choose a pharmacological method of pain relief, including Entonox, the injection of opioids or epidural placement. The commonest opioid used in labour is pethidine administered by intramuscular (im) injection. The effectiveness of pain relief provided by pethidine has long been challenged. Its shortcomings are more serious when set against known side effects including maternal sedation, nausea and potential transfer across the placenta to the foetus. More than a third of women who receive pethidine subsequently require an epidural due to inadequate pain relief. Epidurals provide highly effective pain relief, but increase the risk of a forceps or suction delivery resulting in prolonged hospital stay. Therefore, there is a clear need for a safe, effective, easy to administer analgesic alternative.
Patient Controlled Analgesia (PCA) comprises drug administration into an intravenous drip
with a small dose given each time a woman presses a button, giving her control over her own
pain relief. The pump is programmed to ensure that the maximum dose allowable is within the
safe range. This form of delivery of pain relief matches the drug dose to pain sensation
within the relevant time frame, which is not possible using a single dose intramuscular
injection. Whilst PCA is in widespread use for acute pain relief it has only a limited role
in obstetrics. The most common drug given by PCA is morphine, however, since it has a long
duration of action and crosses the placenta, the potential for accumulation in the foetus and
consequent neonatal sedation at delivery restricts its utility (within obstetrics) to
contexts where neonatal status is not relevant, such as intra-uterine foetal death or foetal
abnormality incompatible with survival.
Remifentanil is a novel synthetic opioid with a very rapid onset (blood-brain equilibration
1.2-1.4 minutes) and short duration of action (context specific half-life 3 minutes), giving
it an analgesic profile which potentially makes it ideal for providing pain relief over 1-2
uterine contractions after a single intravenous dose. It is subject to rapid redistribution
and metabolism by non-specific blood and tissue esterases negating the potential for
accumulation in mother or foetus. Administration of remifentanil by PCA has been investigated
in several small studies in comparison to pethidine and shown to provide useful, although not
complete, pain relief in labour.10-12 Thus far, there is no evidence of detrimental neonatal
effects in comparison to other opioids.
;