Calls for rethink on childbirth pain relief as research shows remifentanil works better than pethidine
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| Women using remifentanil were half as likely to end up asking for an epidural than those given pethidine. |
A new drug to relieve pain during labour works better than pethidine, which has been in widespread use since the 1950s even though it has long been known it does not help all women, say researchers.
Pethidine is given as an injection, but a new study funded by the National Institute for Health Research shows that remifentanil, which women control by pressing a button when they feel pain, appears to be more effective. Women using remifentanil were half as likely to end up asking for an epidural, which blocks all pain and sensation and often leads to a forceps delivery.
Pethidine was the first opioid drug that was allowed to be given by a midwife alone and was very widely adopted, said Dr Matthew Wilson, a senior lecturer at the University of Sheffield and the lead author of the study published in the Lancet medical journal.
More than a quarter of a million women in labour are given pethidine each year in the UK, even though up to 40% do not find it helpful, he said. “Some women do not report any useful pain relief at all and it has significant side effects,” he said. That includes sedation and potentially affecting the baby.
“There has been a longstanding need for something else,” he said. Epidurals are by far the most effective form of pain relief, but women who have them are more likely to end up with their baby having a forceps or vacuum delivery. That can sometimes cause damage to the mother and have long-term consequences, including sexual problems.
Remifentanil is being used in some maternity units, but there has not yet been sufficient proof that it is better than pethidine. Both drugs are out of patent so there is no basic cost differential. The study set out to establish which was the more effective drug, looking at women’s personal experiences of pain and how likely they were to ask for an epidural because the pain relief they were getting was not enough.
Because women are attached to a drip with remifentanil, controlling the dose that goes into their body using a hand-held device, while pethidine is given as an injection, it was not possible to disguise which drug women received in the trial. Over 400 women from centres over the UK took part, but 22 of the women immediately asked for an epidural when they found out they had been randomly assigned to receive pethidine.
Even allowing for those who opted out or delivered before they could be given one of the drugs, half as many women who were given remifentanil ended up having an epidural (19%) as those on pethidine (37%). Those on remifentanil also rated their pain as being less severe on average than those on pethidine in a survey after the birth.
Remifentanil has the big advantage of being cleared from the body very fast – within 10 minutes – so women are able to dose themselves just during contractions. One downside is that it can lead to low oxygen levels. That happened to 14% of women taking the drug, compared to 5% of those on pethidine, and all were given additional oxygen. In the trial, women received one-on-one care from a midwife who could check on their oxygen levels, which is recommended for all NHS maternity units but is not always the case.
The researchers called for a rethink on pain relief for women in labour. “The use of remifentanil PCA as a first-line opioid for pain relief in labour in preference to pethidine would reduce the need for epidurals, instrumental deliveries, and consequent morbidity for large numbers of women worldwide. The implications are that a fundamental re-evaluation of opioid pain relief in labour is required, challenging the routine use of pethidine in childbirth,” they wrote.
Women should have the choice, said Wilson. “Is it reasonable to persist in offering pethidine as standard now that we know remifentanil is superior?” he asked.
Some maternity units stock remifentanil as an alternative for women who cannot have an epidural. “I think our study potentially provides the evidence that the units that currently have the ability to give it should seriously consider opening up to maternal request, provided they can offer the same stand of safety we did [including one to one midwife care],” said Wilson.
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