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BJA Advance Access published online on November 19, 2004
British Journal of Anaesthesia, doi:10.1093/bja/aei029
© 2004 by The Board of Management and Trustees of the British Journal of Anaesthesia
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Accepted October 5, 2004

Clinical Investigation

Is the clinical efficacy of epidural diamorphine concentration-dependent when used as analgesia for labour?{dagger}

G. A. McLeod 1*, B. Munishankar 1, and M. O. Columb 2

1 Department of Anaesthetics, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK
2 Department of Anaesthesia, South Manchester University Hospital, Wythenshawe, UK; Department of Intensive Care Medicine, South Manchester University Hospital, Wythenshawe, UK

* To whom correspondence should be addressed.
G. A. McLeod, E-mail: g.a.mcleod{at}dundee.ac.uk


  Abstract

Background. The physicochemical properties of diamorphine (3,6-diacetylmorphine) enhance its bioavailability compared with more lipid-soluble opioids when administered into the epidural space. However, the influence of concentration, volume or mass on the clinical efficacy of diamorphine is not known.

Method. In this double-blind, randomized, prospective study, 62 women in active labour and ≤5 cm cervical dilatation were recruited to determine whether the mode of action of diamorphine in the epidural space is concentration-dependent. After insertion of a lumbar epidural catheter, patients received epidural diamorphine 3 mg either as a high-volume, low-concentration solution (group A) or a low-volume, high-concentration solution (group B). The concentration of diamorphine was determined by the response of the previous patient in the same group using up-down sequential allocation. Pain corresponding to the previous contraction was assessed using a 100-mm visual analogue score and effective analgesia was defined as ≤10 mm within 30 min of epidural injection.

Results. There was no significant difference in EC50 for diamorphine between the groups: the difference was 15.0 µg ml-1 (95% CI -40.3 to 10.3). The EC50 for group A was 237.5 µg ml-1 (95% CI 221.2 to 253.8) and the EC50 for group B was 252.5 µg ml-1 (95% CI 232.2 to 272.8). The EC50 ratio was 0.95 (95% CI 0.87 to 1.06). The groups exhibited parallelism (P=0.98). The overall EC50 for all data was 244.2 µg ml-1 (95% CI 230.8 to 257.2).

Conclusion. We conclude that diamorphine provides analgesia in labour by a concentration-dependent effect.

Keywords: anaesthetic techniques, epidural; anaesthetic techniques, minimum dose; analgesics opioid, diamorphine.

{dagger} This work was presented by Dr G. A. McLeod to the Anaesthetic Research Society, Aberdeen, 2004.


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G. A. McLeod, B. Munishankar, and M. O. Columb
An isobolographic analysis of diamorphine and levobupivacaine for epidural analgesia in early labour
Br. J. Anaesth., April 1, 2007; 98(4): 497 - 502.
[Abstract] [Full Text] [PDF]


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