The use of neurobehavioural scoring techniques by Scanlon et al in 1974 found that neonates born vaginally to mothers who had received epidural lignocaine and mepivacaine, but not bupivacaine, in labour were "floppy but alert" (1) (Table 35.2). Until further work, ten years later, was found not to confirm the original findings, bupivacaine became the drug of first choice for obstetric epidural analgesia (2).

Lignocaine then came back into widespread use for caesarean section anaesthesia, although bupivacaine remained the agent of choice in labour. Both lignocaine and bupivacaine, in standard doses (Table 36.3), produce minimal direct neonatal depression or neurobehavioural effects, provided that adequate placental circulation is maintained. Bupivacaine, when used to excess, can compromise fetal well-being.

Local anaesthetics are basic drugs that, in plasma, bind predominantly to alpha1-acid glycoprotein. The extent of placental transfer is dependent on the pKa of the drug, the maternal and fetal pH and the degree of protein binding. Fetal hypoxia and acidaemia increase the transfer of these weak bases, producing higher fetal:maternal drug ratios. Acidosis also increases the magnitude of the toxic effects of local anaesthetics in both fetus and neonate.

Bupivacaine is more than 80% protein bound and its placental transfer is relatively less than that of lignocaine, which is 70% protein bound. After epidural administration, the mean Umbilical Vein:Maternal Vein ratio is approximately 0.3 for bupivacaine, and 0.57 for lignocaine (Chapter 50). Spinal anaesthesia (Chapter 63) results in only negligible maternal blood levels of local anaesthetics and is not accompanied by neonatal drug depression.

Groups of mothers receiving epidural analgesia with bupivacaine, when compared to non-epidural groups, have been shown to have improved neonatal outcomes in the following situations: twins (3), Iow-birthweight (4) and pregnancy-induced hypertension (5). In one series of vaginal deliveries, the epidural group of patients scored far better in the majority of neonatal outcome tests than a group given intramuscular pethidine and even outperformed a group given no analgesia (6). Subarachnoid block for Caesarean section has been reported to result in higher one minute Apgar scores and mean umbilical venous pHs than general anaesthesia in a similar group of patients (7).

It is generally believed that neonates delivered by Caesarean section are more alert, quicker to establish spontaneous respiration and less likely to require endotracheal intubation if regional, rather than general anaesthesia, has been used (8, 9), provided that hypotension has been avoided. A fall in blood pressure may reduce placental blood flow (10) and result in depressed neonatal reflexes (11).

In this context, a statement by Reynolds is worthy of repetition: "Provided the maternal circulation is well maintained, both epidural analgesia in labour and regional block for Caesarean section are, if anything, actually beneficial to the baby. It is a pity that women are not told more often of the benefits to the baby of epidural analgesia" (12).

References:
1. Scanlon JW, Brown WU, Weiss JB, Alper MH. Neurobehavioral responses of newborn infants after maternal epidural anesthesia. Anesthesiology 1974 40:1 21-128.

2. Abboud TK, Kim KC, Nouheid R et al. Epidural bupivacaine, chloroprocaine or lidocaine for Cesarean section: maternal and neonatal effects. Anesthesia & Analgesia 1983 62:914-91 9.

3. Crawford JS. A prospective study of 200 consecutive twin deliveries. Anaesthesia 1987 42:33-43.

4. Osbourne GK, Patel NB, Howat RCL. A comparison of the outcome of low birthweight pregnancy in Glasgow and Dundee. Health Bulletin (Edinburgh) 1984 42:68-77.

5. Abboud T, Artal R, Sarkis F et al. Sympathoadrenal activity, maternal, fetal and neonatal responses after epidural anesthesia in the pre-eclamptic patient. American J of Obstetrics and Gynecology. 1982 144:915-918.

6. Corke BC. Neurobehavioural responses of the newborn. The effects of different forms of maternal analgesia. Anaesthesia 1977; 32:539-543.

7. Hodgson CA, Wauchob TD. A comparison of spinal and general anaesthesia for elective caesarean section: effect on neonatal condition at birth. International J of Obstetric Anesthesia 1994 3:25-30.

8. James FM, Crawford JS, Hopkinson R et al. A comparison of general anesthesia and lumbar epidural analgesia for Cesarean section. Anesthesia and Analgesia 1977 56:228-235.

9. Ong BY, Cohen MM, Palahniuk RJ. Anesthesia for Cesarean section - effects on neonate. Anesthesia and Analgesia 1989 68:270-275.

10. Jouppila R, Jouppila P, Kuikka J, et al. Placental blood flow during Caesarean section under lumbar extradural analgesia. British Journal of Anaesthesia 1978 50:275-279.

11. Hollmen AI, Jouppila R, et al. Neurologic activity of infants following anesthesia for Cesarean section. Anesthesiology 1978 48;350-356.

12. Reynolds F. Effects on the baby of conduction blockade in obstetrics. In: Epidural and spinal blockade in obstetrics. Editor: Reynolds F, London: Balliere Tindall p215 1990.