Ultrasound technique for neuraxial procedures
Watford, UK
* E-mail: katnat36{at}hotmail.com
Editor—I read with interest the article about ultrasonic control of the puncture level for neuraxial block in obstetric anaesthesia.1 The authors should be congratulated for the timely publication of this article. However, I wish to comment on the study. In their discussion, they mentioned that they did not find increased BMI had a significant influence on the frequency of errors.
To my knowledge, the arbitary cut-off BMI>30 is not evidence-based in terms of anaesthetic morbidity. If the BMI is >25, it is classified as overweight. The mean BMI in this study was 28. Therefore, this study was carried out in overweight patients. If the study had been done in patients with a BMI>25, the frequency of errors might have been even higher than this study. The last CEMACH report has made recommendations to have local guidelines in the management of obese pregnant women.2 In this context, the NICE guidelines have recommended the use of ultrasound for epidural procedures.3 Therefore, it is time to consider this reliable, easy-to-use technique in the local guidelines in the management of obese patients, while facilitating the training in the use of this technique in obstetric anaesthesia.
Strasbourg, France
* E-mail: pierre.diemunsch{at}chru-strasbourg.fr
Editor—We thank Dr Kathirgamanathan for his interesting comments on our article.1 He raises the fact that the technique used in our study, performed in an overweight population (mean BMI=28), might minimize the frequency of errors in identification of the intervertebral level punctured. It is well known that morbidity and mortality increases in correlation with pre-pregnancy BMI,4 and we agree that a BMI of 30 does not represent a validated cut-off value for the definition of obesity in the obstetric population. Nevertheless, this value is generally accepted as the threshold value for the definition of obesity in the general population. The definition of obesity in the pregnant patient is not clear and the two factors usually evaluated are the pre-pregnancy BMI and the weight gain during the pregnancy.5
We did not aim to address the issue of body weight and BMI in terms of being overweight or obese; however, we are not convinced that a BMI>25 in pregnant women at term truly represents being overweight. Nevertheless, we looked for possible confounding factors during the determination of the lumbar puncture level and arbitrarily took the cut-off value for the definition of obesity in the general population as a surrogate for an ‘overweight threshold’ in the obstetric population at term.
We completely agree with Dr Kathirgamanathan about the growing place for the use of ultrasound in anaesthesia practice, and in particular for spinal procedures. Our study aimed to use the ultrasound technique to demonstrate that the usual anatomical landmarks are frequently misleading in the obstetric population. This, of course, highlights the possible advantages of using ultrasound for the performance of epidurals and spinals in both easy and difficult cases.6 7
References
1 Schlotterbeck H, Schaeffer R, Dow WA, Touret Y, Bailey S, Diemunsch P. Ultrasonographic control of the puncture level for lumbar neuraxial block on obstetric anaesthesia. Br J Anaesth (2008) 100:230–4.
2 Cooper GM, McClure JH. Anaesthesia chapter from Saving Mothers Lives: reviewing maternal deaths to make pregnancy safer. Br J Anaesth (2008) 100:17–22.
3 National Institute for Health and Clinical Excellence. Ultrasound Guided Catheterisation of the Epidural Space (2008) January.
4 Bhattacharya S, Campbell DM, Liston WA, Bhattacharya S. Effect of body mass index on pregnancy outcomes in nulliparous women delivering singleton babies. BMC Public Health (2007) 7:168.[CrossRef][Medline]
5 DeVader SR, Neeley HL, Myles TD, Leet TL. Evaluation of gestational weight gain guidelines for women with normal prepregnancy body mass index. Obstet Gynecol (2007) 110:745–51.[CrossRef][Web of Science][Medline]
6 Grau T, Leipold RW, Conradi R, Martin E. Ultrasound control for presumed difficult epidural puncture. Acta Anaesthesiol Scand (2001) 25:766–71.
7 Kawaguchi R, Yamauch M, Sugino S, Tsukigase N, Omote K, Namiki A. Two cases of epidural anesthesia using ultrasound imaging. Masui (2007) 56:702–5.[Medline]
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