Half as many women in labour given remifentanil to help manage their pain need a subsequent epidural, compared with women given pethidine — the current standard of care, according to a study published in The Lancet.
“Previous studies have shown that at least 1 in 3 women given pethidine to manage pain during labour require a subsequent epidural, as the drug is not always effective,” said Matthew Wilson, MD, University of Sheffield, Sheffield, United Kingdom. “It also has unwanted side effects such as sedation and nausea for the mother, and it may pass into the baby’s bloodstream through the placenta. Our findings challenge the routine use of pethidine for pain relief during labour. Remifentanil reduced the need for an epidural by half and there were no lasting problems for the mothers and babies in our trial, although the effect of remifentanil on maternal oxygen levels needs to be clarified in further studies.”
The study included 400 women aged >16 years who were giving birth after 37 weeks and had requested opioid pain relief. The patients were told about the trial in antenatal visits or when admitted to the hospital to have labour induced, and could sign up to take part when they were in active labour.
For the study, the women were randomised 1:1 to receive remifentanil or pethidine. Remifentanil was given as a patient-controlled drip and women could receive 40 mcg of the drug every 2 minutes by pressing a handheld device, whereas pethidine was given as an injection of 100 mg of the drug into a muscle up to every 4 hours with a maximum of 400 mg in 24 hours. Because of the difference in how the drugs were given, patients and healthcare professionals knew which drug was being used.
All women in the trial received 1-to-1 care from a midwife, with checks on the mother’s breathing rate, sedation, pain ratings, and oxygen levels every 30 minutes. The women could request an epidural at any time, and other pain relief was stopped if an epidural was given.
In the remifentanil group, 93% of women received the drug, and in the pethidine group 77% of women received the drug. The main reasons for not receiving the allocated drug were women giving birth before it could be administered (12 women in the remifentanil group and 17 women in the pethidine group) or the mother deciding to immediately request an epidural after randomisation, without receiving the allocated opioid, which only occurred in the pethidine group (in 22 women).
Half as many women in the remifentanil group went on to have an epidural (19%) than in the pethidine group (41%).
On average, women in the remifentanil group rated their pain as less severe than women in the pethidine group.
Women given remifentanil were also less likely to need forceps and vacuum during labour than women given pethidine (15% vs 26%).
However, remifentanil was associated with twice as many mothers having low oxygen levels than pethidine (14% vs 5%), and more women in the remifentanil group were given supplementary oxygen. Despite this increase, it did not cause any negative effects for the mother or baby, but more research in larger groups will be needed to confirm this.
Breathing problems and sedation in the mother were rare in both groups.
The authors noted some limitations, including that the higher number of women in the pethidine group opting for an epidural immediately could be because they had preconceptions about the effectiveness of pethidine. Once a woman requested an epidural, it would have been unethical to withhold it. However, excluding these episodes from analysis made little difference to the findings, so they had no effect on the result.
Women whose labour was induced were more common in the study than in the general population, as this provides extra time before labour and meant they were more easily recruited into the study. However, being induced is very common, so the authors believe their findings are still relevant.
“In returning to the initial question of whether remifentanil is better than pethidine, we can carefully say yes in view of the efficacy data, with the proviso that the reported effect for this conversion to epidural might have been overestimated by an unknown magnitude, and providing that safety issues are thoroughly addressed,” concluded Peter Kranke, MD, University of Würzburg, Würzburg, Germany. “For all those who would want a more precise answer, this finding gives impetus to further studies, particularly with regards to the selection of women with contraindications or those who express the explicit desire not to have an epidural analgesia. In this scenario, at least the prospect of the gold standard cannot bias the treatment effect.”
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