[Effects of peridural analgesia on labor]

A review of the effects during labour of epidural analgesia on dilatation, expulsion and delivery of the placenta. Uncertainties in knowledge of the precise organisation of uterine innervation and of the intrinsic innervation of the organ render the study of changes in uterine contraction and in cervical resistances difficult. At circulating levels higher than those found in clinical practice, local anaesthetics have a definite oxytocic e-fect, local anaesthetics have a definite oxytoci effect, whilst adrenalin is a powerfult tocolytic. By contrast, the indirect effects related to neurolysis in extradural analgesia are negligeable. Cervico-segmentary resistances are decreased. In practice, there is no increase in the period of dilatation in the absence of any haemodynamic disturbances and if mixtures containing adrenalin are avoided. Expulsion is favourised by muscular relaxation but impaired by the lack of voluntary expulsive effort, hence the choice of a local anaesthetic with the lowest possible motor effect. Delivery of the placenta, which involves only uterine contraction, which is not affected, may be accelerated by oxytocics.