HOW EFFECTIVE ARE OPIOID DRUGS IN RELIEVING PAIN?
This question is not easy to answer. First of all, it obviously depends on how severe the pain is. For this reason, opioids are more effective in early labour than later on, when the contractions are much stronger. Most mothers feel that they get some degree of relief, and a minority of women find that a single injection is all they need. Many women also feel calmer and more relaxed. Others, however, experience little benefit - presumably because the pain is so intense - or, they may dislike the accompanying side effects. One large survey (from the Hammersmith Hospital in London) revealed that only 22 per cent of women received satisfactory pain relief using pethidine alone, and 48 per cent experienced 'no relief whatsoever'.
Opioid drugs are more reliable in treating postoperative pain - where the pain is usually less severe and more constant. Women who have experienced perfectly satisfactory pain relief with opioid drugs in the past (e.g. following surgery) should not assume, therefore, that they will find them equally effective during labour.
Second, the effectiveness of opioid drugs depends on the dose that is given. The bigger the dose, the more effective the pain relief. But there is a price to pay using larger doses: namely, an increased incidence in side effects. In the distant past, it was not uncommon for opioid drugs to be given in such large doses (often combined with sedatives) that women could hardly remember having a baby at all. According to a survey published in 1952, it was not unusual for women to receive doses of pethidine six or eight times the doses that are used today!
Nowadays, much smaller doses of opioids are given during childbirth and there is really no logical reason at all for routinely using sedative drugs (e.g. barbiturates). It has been shown that sedatives only exacerbate fatigue without contributing anything towards pain relief. They also cross the placenta very easily but (unlike opioids) their effects cannot be reversed. Sedatives are eliminated from the body slower than opioids, and have been said to reduce the baby's muscle tone for a while after delivery as well as interfering with normal regulation of body temperature. Despite these drawbacks, many centres continue to add a sedative whenever an opioid drug is given during labour. But they really have little merit - apart from reducing nausea (and even then, there are more suitable drugs available). Sedatives may have been partly to blame for the reputation that opioid drugs have had in some places for causing mental confusion in the mother and poor adaptation in the baby. The reader is encouraged to enquire whether sedative drugs are usually given in addition to an opioid during labour. If so, you can always request that the sedative be omitted.
Finally, the effectiveness of opioid drugs depends on where, and how, they are given. For example, the dose requirements are considerably less when they are given close to their main site of action (the spinal cord) rather than having to be 'delivered' there, via the circulation. The dose requirements are usually more than halved compared with intramuscular injections. Unfortunately, most studies have shown that, by themselves, epidural opioids provide disappointing pain relief during labour. When combined with a local anaesthetic, however, epidural opioids can provide very effective pain relief.
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