If you wish to respond to a paper or other item already published in the BJA, please go to the abstract/full text version of that item and click on the link "E-Letters: Submit a response to the article".
Electronic Letters to:
|
|
E-letters: Electronic letters published:
-
![[Read E-letter]](/icons/misc/sectionDOWN.gif)
Safety with the Oxford Miniature Vaporiser
- Ivan T Houghton (11 April 2007)
-
Responce to E letter titled "Sev'n'ox analgesia, why does it work" (15th Feb 2007) by Dr Matthew Way
- Seng T Yeo (26 February 2007)
-
Sevo'n'ox analgesia, why does it work?
- Matthew R Wayman (16 February 2007)
|
|
|||
|
Ivan T Houghton, Retired Military Anaesthetist London Metropolitan University
Send letter to journal:
|
Editor Yeo and colleagues (1) used the Oxford Miniature Vaporiser (OMV; Penlon Ltd, Oxford, UK) to deliver sevoflurane in a self-administered system for obstetric analgesia. This vaporiser is very versatile and has been used successfully for over forty years with a number of different volatile anaesthetic-agents. Unfortunately one of its major defects is that if the vaporiser is tipped over, pure-liquid anaesthetic-agent may leak out and give an excessive dosage of the agent with a resulting cardiac arrest (2). For this reason, the Triservice vaporiser (the military version of the Oxford Miniature Vaporiser) is supplied with a folding base and a standard hook on the back to attach it to the side bar of a trolley or operating table (3). For safety, it is suggested that anybody copying Yeo and colleagues’ method should ensure that the vaporiser is properly secured. I. T. Houghton London, United Kingdom E-mail ivanhoughton@doctors.org.uk References 1. Yeo ST, Holdcraft A, Yentis SM, Stewart A. Analgesia with sevoflurane during labour: I. Determination of the optimum concentration. Br J Anaesth 2007; 98(1): 105-9. 2. Munson WM. Cardiac arrest: hazard of tipping a vaporizer. Anesthesiology 1965; 26: 235. 3. Houghton IT. The Triservice anaesthetic apparatus. Anaesthesia 1981; 36: 1094-108. Conflict of Interest:None declared |
|||
|
|
|||
|
Seng T Yeo
Send letter to journal:
|
I would like to thank Dr Matthew R Wayman on his recent letter regarding our research study (1,2). Dr Wayman has a valid point with respect to sevoflurane’s influence on uterine contractility reported by in vitro studies and how this may affect pain experienced and efficacy of labour contractions during childbirth (3,4). However, if sevoflurane’s analgesia was cause by a tocolytic effect, we would have expected a reduction in pain intensity scores which was not observed (5). Assessing the direct effect of sevoflurane on uterine contractility in vivo was not and has never been conducted and therefore we would agree that further research would be required to investigate this phenomenon prior to widespread use of sevoflurane. In addition, we had considered insertion of an intrauterine pressure monitor to observe sevoflurane’s in vivo effect; however the ethical issues of risks to the mother proved to be overwhelmingly challenging. In conclusion, we agree that the mechanism of analgesia still remains unclear. We do not believe that it is a tocolytic effect but feel that perhaps an effect at the higher centres would explain the pain relief benefits without the alleviation of pain intensity with the use of sevoflurane. References: 1. Yeo ST, Holdcroft A, Yentis SM, Stewart A. Analgesia with sevoflurane during labour: I. Determination of the optimum concentration. Br J Anaesth 2007; 98:105-9 2. Yeo ST, Holdcroft A, Yentis SM, Stewart A, Bassett P. Analgesia with sevoflurane during labour: II. Sevoflurane compared with Entonox for labour analgesia. Br J Anaesth 2007; 98:110-15 3. Yidiz K, Dogru K, Dalgic H, Seria IS. Inhibitory effects of desflurane and sevoflurane on oxytocin-induced contractions of isolated pregnant human myometrium. Acta Anaesthesiol Scand. 2005; 49: 1355-9 4. Yoo KJ, Lee JC, Yoon MH, Shin MH. The effects of volatile anesthetics on spontaneous contractility of isolated human pregnant uterine muscle: a comparison among sevoflurane, desflurane, isoflurane, and halothane. Anaesth Analg. 2006; 103: 443-7 5. Corli O, Grossi E, Roma G, Battagliarin G. Correlation between subjective labour pain and uterine contractions: a clinical study. Pain 1986:26(1);53-60 Conflict of Interest:None declared |
|||
|
|
|||
|
Matthew R Wayman, SpR Anaesthetics Northern Schools of Anaesthesia
Send letter to journal:
|
I read with interest the recent original research and accompanying editorial regarding the use of sevoflurane for labour analgesia (1-3). As Yeo et al acknowledge, the mechanism by which sevoflurane is able to produce labour analgesia remains unclear (3), especially as sevoflurane has not been found to be analgesic in human laboratory studies(4). The authors postulate that the analgesic effect of sevoflurane in the labour setting may be due to the visceral nature of labour pain. Another hypothesis could be considered however, which may have important clinical implications. Sevoflurane has been shown to decrease both the amplitude and frequency of oxytocin induced contractions in isolated pregnant human myometrium (5,6), with the effect persisting to the lowest concentrations studied. Could it be possible therefore that it is through a reduction in the strength of uterine contractions that sevoflurane has its analgesic action? And if so would this tocolytic effect also have the potential to adversely affect the progress of labour? As Toscano et al point out in their pilot study into the use of sevoflurane in labour, the effect sevoflurane administration has on duration, force and frequency of contractions remains to be established (7). It seems important to investigate these areas prior to more widespread use of sevoflurane in the labour setting. References: 1.McClure J. Sevoflurane analgesia in labour (sevo’n’ox). Br J Anaesth 2007;98: 1-2 2.Yeo ST, Holdcroft A, Yentis SM, Stewart A. Analgesia with sevoflurane during labour: I. Determination of the optimum concentration. Br J Anaesth 2007; 98:105-9 3.Yeo ST, Holdcroft A, Yentis SM, Stewart A, Bassett P. Analgesia with sevoflurane during labour: II. Sevoflurane compared with Entonox for labour analgesia. Br J Anaesth 2007; 98:110-15 4.Janiszewski DJ, Galinkin JL, Klock PA. The effects of subanaesthetic concentrations of sevoflurane and nitrous oxide, alone and in combination, on analgesia, mood and psychomotor performance in healthy volunteers. Anesth Analg 1999;88: 1149-54 5.Yidiz K, Dogru K, Dalgic H, Seria IS. Inhibitory effects of desflurane and sevoflurane on oxytocin-induced contractions of isolated pregnant human myometrium. Acta Anaesthesiol Scand. 2005; 49: 1355-9 6.Yoo KJ, Lee JC, Yoon MH, Shin MH. The effects of volatile anesthetics on spontaneous contractility of isolated human pregnant uterine muscle: a comparison among sevoflurane, desflurane, isoflurane, and halothane. Anaesth Analg. 2006; 103: 443-7 7.Toscano A, Pancaro S, Giovannoni G. Sevoflurane analgesia in obstetrics: a pilot study, Int J Obstet Anaesth 2003; 12: 79-82 Conflict of Interest:None declared |
|||