Analgesia with sevoflurane during labour: i. Determination of the optimum concentration

Abstract

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.