The best local anaesthetic for pain relief is the long-acting amide, bupivacaine, which is unlikely to give rise to cumulative local anaesthetic toxicity when used in the usual therapeutic dose range (1), and is safe for the fetus and neonate. Lignocaine (lidocaine) is suitable for establishing analgesia, or rapidly augmenting an epidural anaesthetic for instrumental or Caesarean delivery (2). Ropivacaine, to be released in 1996, appears to have very similar clinical sensory and motor characteristics to an equivalent concentration of bupivacaine, when used as a sole agent (3, 4) (Chapter 4).
Because 0.125% bupivacaine with epinephrine is only effective in selected populations (5, 6), I would recommend that initial pain relief be obtained using either 0.25% bupivacaine, or 0.125% with opioid (7). The latter has the advantage of being both a test and therapeutic dose (8). If administered by intermittent bolus, the addition of fentanyl to bupivacaine provides greater maternal satisfaction than bupivacaine alone (9).
There are few controlled comparisons of epidural opioids during labour, so that the choice often depends on local availability, cost and prescriber familiarity. Morphine is unsuitable, due to its slow onset and high incidence of side effects. Fentanyl, sufentanil, diamorphine and pethidine are popular and, when used appropriately, appear safe for the healthy, term infant. Only fentanyl and sufentanil have been evaluated extensively in this setting. The optimal concentration of intermittent bolus bupivacaine with opioid is 0.125%, and the most suitable dose of opioid is fentanyl 50mcg (6, 10, 11), sufentanil 7.5 mcg (12), or pethidine 25mg (13). Fentanyl 100mcg may be indicated in certain circumstances (14, 15).
For maintenance of pain relief by patient-controlled epidural analgesia (PCEA), bupivacaine 0.0625 to 0.125% with either fentanyl or sufentanil allows the majority of parturients to remain ambulant and produces less motor block than 0.25% bupivacaine (16). PCEA is associated with an overall reduction in the amount of drug used when compared with other techniques. Adrenaline significantly increases the degree of motor block (17) (Figure 60.1). A recommended solution is 0.1% bupivacaine with fentanyl 2 mcg/ml given as a 5ml incremental bolus on demand (18). A continuous infusion technique using bupivacaine 0.125% at 10-15ml/hr is effective. The addition of fentanyl allows the concentration of bupivacaine to be reduced to 0.0625% whilst efficacy is retained and motor block diminished (19). Success has also been reported a with combination of 0.01% bupivacaine, sufentanil and epinephrine (20). When given by infusion at 7.5mls/hr, bupivacaine 0.125% with diamorphine 0.0025% was more efficacious than bupivacaine 0.125% with fentanyl 0.0002%, but both combinations produced better analgesia than bupivacaine alone (21). The addition of sufentanil 10mcg/hr is better than fentanyl 20mcg/h (20).
References:
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7. Russell R Int J Obstet Anesth 1993;2:78
8. Van Zundert A Anesthesiology 1988;69:998
9. Murphy J, Henderson K, Bowden MI, Lewis M, Cooper GM. Bupivacaine versus bupivacaine plus fentanyl for epidural analgesia: effect on maternal satisfaction. Br Med J 1991;302:564-7
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18. Paech M Int J Obstet Anesth 1996 5: in press
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20. Cohen S Anesth Analg 1992;74:S47
21. Enever G, Noble HA, Kolditz D, Valentine S, Thomas TA. Epidural infusion of diamorphine with bupivacaine in labour. A comparison with fentanyl and bupivacaine. Anaesthesia 1991;46:169- 73