Bailliere's clinical obstetrics and gynaecology最新文献

For a number of reasons, bupivacaine has become the most frequently used local anaesthetic in obstetric anaesthesia, despite the fact that it has a narrower margin of safety than other local anesthetics. In recent years, advances in technology have made singleisomer formulations of drugs available for clinical use. Generally speaking, the levo stereoisomer of amide local anaesthetic has a lowe rpotential for systemic toxicity than the dextro form of the drug while retaining anaesthetic potency. Ropivacaine (Naropin^®, Astra Ltd), a homologue of mepivacaine and bupivacaine, has recently been released for use. Its clinical efficacy appears to be quite similar to that of bupivacaine but it has a greater margin of safety. The other drug currently being investigated is levobupivacaine (Chirocaine^®, Chiroscience Ltd). Both drugs appear to be similar in efficacy to the currently used formulation of bupivacaine; however, they are more costly. Thus, cost-benefit analyses are required to define more clearly their future role in obstetric anaesthesia.

The potential effects of epidural analgesia on the progress and outcome of labour have been the subject of lasting controversy. Retrospective reviews indicate that epidurals are associated with longer labours and/or an increase in the incidence of instrumental or operative delivery. Similar results were obtained in non-randomized prospective studies. None of them established a causal relationship, because without randomization the selection bias cannot be ruled out. Other factors, such as premature rupture of membranes and maternal socioeconomic status, may affect the outcome of labour. It was also reported that introduction of the on-demand epidural service did not increase the primary caesarean section rate. The few prospective randomized studies are contradictory and not very reliable owing to small patient populations and high cross-over rates. There is, however, unanimity among the authors regarding the superiority of pain relief provided by epidural blocks over systemically administered opioids.

Substance abuse remains a major problem in society, while substance abuse in pregnancy has emerged as a major health problem in the 1990s. Due to this trend, obstetricians, neonatologists and anaesthesiologists are encountering an increasing number of pregnant patients who use licit and illicit substances. The use of these substances presents a multitude of problems for the patient, her unborn child, and the physicians involved in their care. The following article reviews the various substances of abuse used by pregnant women and the implications of their use for analgesia and anaesthesia during labour and delivery. In conclusion, it is essential for physicians to identify the substance abusing parturient to optimize care of these patients and be prepared for the crises that may arise.

Women frequently use a mixture of analgesics to gain relief from the distress of childbirth and antenatally require information on their effectiveness and side-effects. One such example would be the reported long-term neonatal behavioural changes following systemic opioids such as pethidine. The most frequently reported maternal effects of epidural or spinal analgesia are prolonged symptoms of headache, backache and neurological sequelae. Large retrospective studies of postpartum symptomatology have focused on correlations with regional nerve blockade rather than on other more commonly used analgesics. Post-dural puncture headache is a recognized long-term complication of epidural nerve blockade. However, prospective studies have not confirmed any causal relationship between epidural analgesia and backache and neurological complications are five times more common after childbirth itself than after regional nerve blockade. Postpartum symptomatology describes significant morbidity in the community but its relationship to analgesia in labour is still to be proved.

Epidural analgesia and spinal analgesia are the most effective techniques for relieving labour pain. Basically, local anaesthetics (i.e. bupivacaine) and opioids (i.e. fentanyl or sufentanil), especially when combined, produce excellent analgesia with minimal motor blockade. However, none of these agents is devoid of side-effects and analgesia remains sometimes imperfect, suggesting that new drugs would be welcome. Adrenalin and clonidine act on a₂-adrenoceptors in the spinal cord and both have been found to improve analgesia. These two drugs have already been used in many patients and studies because the absence of neurotoxicity has been well documented. Clonidine looks more attractive, although sedation and hypotension limit its use. Other analgesic drugs are promising alternatives but are still at an experimental or very early clinical stage. Neostigmine and ketamine (without preservative) are not neurotoxic while midazolam neurotoxicity is still controversial. Intravenous remifentanil might prove useful when neuraxial analgesia is contraindicated.

Satisfaction with childbirth is a multidimensional issue, of which analgesia is but one component. The importance of analgesia as a contribution to overall satisfaction has been recognized increasingly in the last 50 years, but improvement in quality of available analgesia has not always resulted in commensurate improvement in satisfaction. Satisfaction by its very nature has proved to be difficult both to define and to quantify, and no reliable standards of measurement have been accepted. Pain relief in childbirth is subject to many social and cultural modifiers, which continue to change. Control of pain rather than absolute amelioration is seen by many to provide greater satisfaction. Analgesia issues still do not figure prominently in the overall satisfaction of the birthing process for the vast majority of women, despite the availability of and demand for improved methods of relief. The interpersonal relationships established between patient and healthcare providers may ultimately be of more importance in the determination of satisfaction with management.

Labour pain is the result of many complex interactions. Although not fully determined, the pain arises from distension of the lower uterine segment and cervical dilatation. The neural mechanism of labour has some features similar to other forms of acute pain; nociceptive information is relayed in small A delta and C afferent fibres to the dorsal horn of the spinal cord, mediated by neurotransmitters; from there it may be involved in the initiation of segmental spinal reflexes or pass through the spinothalamic tract to the brain. Many factors are activated during labour which may modify the nocioceptive impulse at different stages of its passage. Some of these factors act synergistically to promote anti-nociception that peaks at delivery.

Childbirth is frequently accompanied by pain. For religious, cultural and philosophical reasons many groups have sought to prevent treatment of pain. Pain may have adverse effects on the mother and fetus. The psychological effects of severe pain should not be overlooked particularly where it is associated with an adverse fetal or maternal outcome. There are a number of different forms of pain relief in labour with differing side-effects and efficacies. The controversy concerning medical management of women in labour has been used to dissuade women from requesting pain relief. This debate has encouraged the use of a patient-centred philosophy of care that encourages the patient to retain control. However, good pain relief may allow the women to retain control if administered in a sensitive manner. The ideal analgesic in labour is discussed. Recent and future developments of analgesia in childbirth are discussed with respect to this.

Systemic labour pain treatment with opioids and inhaled nitrous oxide has for many decades frequently been used in medically developed countries. Self-administered nitrous oxide (50% in oxygen) has never gained the same popularity in the USA as in the UK or Scandinavia but the use of opioids, mainly pethidine, has generally been widespread in spite of well-known negative effects on the postnatal adaptation of the newborn. Since the often very intense labour pain seems to respond very poorly even to highly sedating doses of parenteral opioids, their frequent use during delivery and parturition has to be questioned. Self-administered inhalation of nitrous oxide 50% in oxygen also has a limited efficacy for relieving labour pain but because it is mainly devoid of adverse effects on the baby or on the parturient its future use in obstetrics can be defended more easily, either as a sole agent in women with low labour pain scores or in early labour preceding epidural analgesia.