[Effect of epidural analgesia on obstetrical mechanics].

Epidural analgesia is the most effective technique of pain relief during labour. However, there is an old suspicion that it modifies the course of labour. This deleterious effect has recently been demonstrated in studies showing that epidural analgesia using local anaesthetics increases the duration of the second stage of labour and the incidence of instrumental delivery in nulliparous women with fetus in vertex presentation. No such clear data exist for other obstetrical situations. The deleterious effect on the second stage is primarily due to motor blockade of the pelvic floor muscles which normally exert an important influence on fetal accommodation. It is possible to limit the negative effect of motor blockade by using either a combination of low-dose bupivacaine and opioid, or injection of a lipophilic opioid through a subarachnoid catheter, or by using the new amide local anaesthetic, ropivacaine, which is claimed to possess less motor blocking action.