Combined spinal-epidural analgesia (CSE) in labour is a new approach to pain relief which uses an initial dose of subarachnoid opioid, usually with bupivacaine, to rapidly achieve analgesia (Figure 61.1) (Chapter 62). This is followed by conventional epidural therapy for maintenance, if required. There are, to date, no dose-response and few comparative studies of subarachnoid analgesic solutions, so suggestions are based on clinical experience and dose-response studies of subarachnoid opioid alone during labour.
When used as sole agents in early labour, effective analgesic doses of subarachnoid opioid which are associated with an acceptable incidence of nausea and pruritus lie in the range of 3 to 10mcg sufentanil (1, 2, 3) and 15 to 25mcg fentanyl, although the optimal doses may be 10mcg and 15mcg respectively (4, 5, 6). Sufentanil may be superior to fentanyl (7), although it can also cause more pruritus (8). Pethidine (meperidine) 10mg appears to be more effective than both, especially in late labour (3), but has not been investigated as part of a CSE regimen (Figure 61.2). There appears to be little merit in combining morphine with a lipophilic opioid, since side effects and the risk of respiratory depression may be increased (9, 10).
Bupivacaine alone is unsatisfactory, since doses of 2.5 to 5.0mg do not reliably produce good analgesia and the 5mg dose results in a high incidence of dense motor block (11, 12) .
The combination of bupivacaine and opioid improves pain relief compared with either drug alone (11), and seems the best approach (13, 14) (Figure 61.3). No demonstrable neonatal effects have been shown and although significant falls in blood pressure may occur in the first 30 minutes, thereafter, it is safe to ambulate and most women are capable of doing so (13, 14, 15). The optimal combination has yet to be determined, with some authors favouring as little as 1mg of bupivacaine with opioid (14,16). Because of a synergistic analgesic effect, the optimal dose of opioid may also be reduced in combination regimens.
The addition of adrenaline (epinephrine) by some investigators (14, 16) has not been confirmed as beneficial in this setting, and may increase nausea without improving analgesia (2). Studies of the influence of the volume of injectate on clinical response show no difference when 10 mcg of subarachnoid sufentanil (with no local anaesthetic) was administered in 1, 2 or 3ml of solute (17, 18).
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