LABOR ANALGESIA - A RISK-BENEFIT ANALYSIS

The pain associated with labour can be severe. The ideal labour analge sic does not exist and systemic opioids provide little relief. Nausea, vomiting and sedation are common adverse effects of systemic opioids. Paracervical block can relieve only the pain of the first stage of la bour. The duration of analgesia obtained using paracervical block is l imited and repeat blocks increase the risk of direct fetal injection. Epidural analgesia effectively relieves labour pain. The insertion of an epi dural catheter can provide continuous analgesia throughout labo ur. In addition, the catheter can be used to provide surgical anaesthe sia, should operative delivery be required. Epidural local anaesthetic s commonly produce maternal hypotension and motor blockade. However, o pioids potentiate the effect of epidural local anaesthetics. Thus, con comitant epidural opioid injection allows the use of lower concentrati ons of local anaesthetics, decreasing the frequency and severity of hy potension and motor blockade. Epidural analgesia has other, potentiall y catastrophic, adverse effects but, with safe clinical practice, thes e problems are extremely rare. Intrathecal injection of opioids or loc al anaesthetics also provides effective labour analgesia. However, no single intrathecal drug or drug combination reliably provides analgesi a for the duration of labour. Many clinicians use both intrathecal and epidural analgesia as a combined spinal-epidural technique. This appr oach provides the rapid onset of intrathecal drugs and the flexibility of continuous epidural block. Fetal heart rate decelerations occasion ally follow the use of any of the above labour analgesic techniques. M ost studies of the aetiology of fetal heart rate decelerations have fo cused on factors unique to each analgesic technique. However, the simi lar timing and appearance of fetal bradycardia suggests a common cause . Induction of maternal analgesia may transiently alter the balance be tween factors encouraging and inhibiting uterine contraction. A tempor ary increase in the uterotonic effects of endogenous or exogenous oxyt ocin may then produce a tetanic uterine contraction with subsequent de crease fetal oxygen delivery and resultant fetal bradycardia. Regardle ss of aetiology, these bradycardias are transient and should not produ ce maternal or fetal morbidity. Much controversy surrounds the effects of analgesia, especially epidural block, on the course and outcome of labour. Various studies have reported that epidural analgesia slows l abour, increases the incidence of malposition of the fetal head, incre ases the need for forceps delivery and increases the risk of caesarean delivery. Most of the studies reporting these effects are retrospecti ve and nonrandomised. More careful studies suggest that specific anaes thetic techniques (i.e. local anaesthetic-opioid mixtures) or obstetri cal management can limit or eliminate these 'risks' of epidural labour analgesia.