Relief of Obstetric Pain
Dr J C D Wells, Liverpool, UK
Obstetric pain has been around as long as mankind has existed. Many analgesic methods were known four thousand or more years ago, and the prevalence of pain during childbirth, and the importance attributed to it, are found in the writings of ancient Babylonians, Egyptians, Chinese and Greeks (Bonica, JJ, 1953: The Management of Pain, Philadelphia).
And yet in the English speaking Western world, in the eighteenth century, no analgesic was proffered. The religious dictum In sorrow shalt thou bring forth children held sway. It was only when Queen Elizabeth took inhalation anaesthesia that analgesia became fashionable and permissible in labour. A myth existed right up to the late 50s, (e.g., Lamaze, 1956) which felt that natural childbirth in the primitive races was painless. However, careful research has shown this to be totally untrue.
Certainly for the last 150 years many techniques have been used to provide analgesia in labour. These include psychological, pharmacological, inhalational and regional analgesia. Much debate has taken place as to the merits of the various techniques.
In this new Millennium, with an emphasis on evidence-based medicine, scarcely can there be a more fertile field. Some of the myths and beliefs of medical and nursing staff as to relative efficacy and safety of analgesics do not bear up to close scrutiny. By evidence-based, I mean that clinical decisions should be based on the best available scientific evidence, and what now can we say about this?
Opioids can be given by many routes. We can consider the oral, sublingual and buccal routes, intramuscular or intravenous, rectal, subcutaneous, epidural and intrathecal. Clearly, in obstetrics the oral route is unlikely to be applicable, and there are no significant trials on sublingual, buccal or rectal administration. The choice of route is largely intramuscular/intravenous/subcutaneous, versus epidural/intrathecal. In each of these routes we need to consider what agents might be most effective, which are cost-effective, what are the side-effects to the mother and what are the side-effects to the foetus.
Protocols involving complex polypharmacology, with the addition of Cyclizine, Ramitidine or local anaesthetic have now been tested in many centres. The enthusiast argues that carefully administered opioids can produce adequate analgesia, with a modicum of side-effects and little disturbance of the normal labour (Kingdom, J and Woods S, 1997, The Lancet, 349;726). They point out that when epidurals are performed, using standard local anaesthetics, 54 per cent will have Caesarian section, forceps or ventouse to delivery.
Lets consider common practice in most units. In the UK and in other countries, many patients are given either inhalation analgesia or intramuscular pethidine by the nursing staff. This is given with the belief that pethidine causes less side-effects in the mother, produces adequate analgesia and is less likely to cause neonatal depression and other side-effects. In practice, pethidine is equianalgesic with morphine, and some studies suggest that the analgesia is very poor (Olofsson et al, B J Obs & Gynae, October 1996).
These authors point out that recent studies show fast morphine clearance in women in labour, with low or undetectable concentrations in the newborn. Pethidine analgesia, however, often affects neonatal performance up to several days post-partum, especially at intrauterine exposure times of around 2 to 3 hours. In a double-blind, randomised study, pethidine was found to produce more nausea and vomiting than morphine. Both produced marked sedation and both produced poor analgesia.
The authors go on to conclude that good analgesic effects from parenteral opioids occur only due to retrospective patient interviews following delivery, and suggest that the method is due to profound sedation and amnesia rather than any inherent analgesic effect. They question the ethics and medical correctness of this technique.
Felicity Reynolds (London, WB Saunders, 1993) points out that we continue to offer systemic opioids despite ineffectiveness, because we believe they are safe. However, she states that confidential inquiries into neonatal deaths in the UK reveal 14 deaths in the past 6 years from gastric aspirational respiratory problems in which systemic opioids were involved. She goes on to point out that 12,000 mothers were asked in 1990 if there was analgesia from systemic opioids, and they said no.
Diamorphine is used in some places, but there seems no evidence to prove that this is any better than morphine or pethidine. Other opioids used systemically are likely to fall if close scrutiny is introduced.
Is there then no place for opioids in modern obstetric analgesic practice? Clearly, one of the problems with local anaesthetic epidural blockade is excessive sensory block, leading to the lack of sensation of labour, with potential psychological sequelae in lack of bonding and so on. Also, increased interventional deliveries due to lack of appreciation of pushing or even frank motor blockade. In the last 20 years opioids have been used epidurally and then intrathecally, with a view to examining their place in pain relief.
Epidural opioids appear relatively ineffective, probably because CNS penetration is poor, in the time available, and also because the epidural space is richly supplied with blood vessels and there is a fairly high systemic effect. On the contrary, intrathecal narcotics appear to be effective. The problems are length of efficacy and potential side effects.
Many authors have contributed papers in the last decade on intrathecal narcotics. I will review some:-
Lyman Rust, in the American Journal of Obstetrics and Gynaecology, June 1994, pp 1643-1648, states Intrathecal narcotics offer excellent labour pain relief with manageable side-effects and without adverse obstetric outcome. He used a protocol combining Fentanyl, 25 to 30 mcg, morphine, 0.25 to 0.3 mg and Lignocaine, 1 per cent, 6 to 8 mg. This was injected into the CSF between L2/3 and L4/5, in the first stage. In second stage, either a pudendal block or local anaesthetic was given if needed. All patients received nalbuphine intravenously within 15 minutes of delivery and naltrexone, 12.5 mg orally within 30 minutes of delivery. All patients received metoclopramide 10 mg intravenously, 6-hourly for nausea and vomiting. They looked at 90 patients out of a total of over 3000 who had intrathecal narcotics. Over one-third of patients had pruritis, the majority requiring naloxone. No patients experienced headache severe enough to require any treatment other than analgesics. There was an equal number vomiting in the control group. There was increased urinary retention in the intrathecal patients, but none experienced respiratory depression. There was a greater likelihood of a vaccuum extraction, but no greater likelihood of forceps delivery.
Fox and Rowbotham (British Medical Journal, 1999, 319;557-560) reported that mobile epidurals were a recent advance in obstetric anaesthesia. They discussed the mixture
of opioids such as Fentanyl with local anaesthetic, to minimise motor block. They pointed out that large, multi-centre studies are in progress to compare mobile epidurals with conventional epidurals. We will have to await the results with interest!
Arkoosh et al, in 1994, used Fentanyl and morphine versus Sufentanyl and morphine, double-blind, and concluded that both produced adequate labour analgesia, but only for 2 hours. Patients receiving Sufentanyl experienced more severe pruritis.
Zapp and Thorne (Military Medicine, 1995) looked at 150 labouring patients and treated them with intrathecal morphine, 0.25 mg, and Fentanyl 25 mcg. They reported good pain control but did not discuss side effects or length of efficacy.
In conclusion then, the future of opioids in obstetric analgesia would appear to be intrathecal administration with perhaps epidural administration having to prove its case now rather than being assumed to work. Complex regimes will have to be assessed, by double-blind comparative studies, to determine the best mixture, optimal efficacy and minimisation of side-effects. It is fairly clear that no method is going to be side-effect free, or universally effective, and all methods will be more costly (but hopefully more effective) than inhalational anaesthesia or intramuscular opioids administered by midwives alone, which in truth appear to be of limited efficacy.
When I was doing my obstetric anaesthesia in 1979, I combined an epidural catheterisation with an intrathecal injection through the Tuohy needle, before insertion of the catheter. This combination technique is used by some, and also needs evaluation.
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