Analgesia with sevoflurane during labour: I. Determination of the optimum concentration
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1 Magill Department of Anaesthesia, Imperial College London, Chelsea and Westminster Hospital 369 Fulham Road, London W12 0HS, UK
2 East Surrey Hospital, Canada Avenue Redhill, Surrey RH1 5HR, UK
3 Present address: Hereford Hospitals NHS Trusts Hereford HR1 2ER, UK
*Corresponding author: Anaesthetic Department, The County Hospital Union Walk, Hereford HR1 2ER, UK. E-mail: sengyeo{at}hotmail.com
Background. Sevoflurane has favourable physical qualities for inhaled analgesia during labour pain. The aim of this preliminary study was to identify its optimum concentration.
Methods. In this open-labelled escalating-dose study, 22 parturients in labour self-administered sevoflurane at 10 contractions using an Oxford Miniature Vaporiser. The inspired concentration was increased by 0.2% after each contraction from 0% to 1.4% or decreased if sedation occurred. Visual analogue scores (0–100 mm) for pain intensity, pain relief, sedation, mood and coping were measured after each contraction.
Results. The median (IQR [range]) pain relief and sedation scores increased from 44 (43–56 [4–93]) mm and 55 (43–56 [0–98]) mm at 0.2% sevoflurane, to 74 (72–78 [50–80]) mm and 71 (71–73 [33–97]) mm at 1.2% sevoflurane, respectively. Pain relief scores did not show any significant increase above 0.8% whilst sedation continued to increase, with excessive sedation occurring at 1.2% sevoflurane. No significant changes in other scores were measured.
Conclusions. We concluded that the optimal sevoflurane concentration in labour was 0.8%. This concentration allows a safety margin and balances the risk of sedation with the benefit of pain relief in labour.
This research has been presented at the Obstetric Anaesthetists' Association Annual Meeting 2003 and published as the following abstract: ‘Inhalational Analgesia using Sevoflurane: a pilot study’.
This article is accompanied by Editorial I.
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