Analgesia with sevoflurane during labour: i. Determination of the optimum concentration.
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.
Yeo
S T
ST
Magill Department of Anaesthesia, Imperial College London, Chelsea and Westminster Hospital, 369 Fulham Road, London W12 0HS, UK. sengyeo@hotmail.com
Holdcroft
A
A
Yentis
S M
SM
Stewart
A
A
D000223:Adaptation, Psychological / Q000187:drug effects; D000328:Adult; D016362:Analgesia, Obstetrical / Q000379:methods*; D016058:Analgesia, Patient-Controlled / Q000379:methods; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008738:Methyl Ethers / Q000008:administration & dosage*; D010147:Pain Measurement / Q000379:methods; D010865:Pilot Projects; D011247:Pregnancy; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane