Changes in Doppler velocimetry of uterine arteries during labour analgesia
London, UK
Email: felicity.reynolds{at}btinternet.com
Editor—I was interested to read the study by Chen and colleagues1 in which they measured uterine artery resistance during the course of labour and after delivery in 20 women who received epidural analgesia. The paper is called ‘The effects of continuous epidural analgesia on Doppler velocimetry of uterine arteries during different periods of labour analgesia’ and concludes ‘Continuous epidural analgesia with bupivacaine 0.075% increases the resistance of uterine artery and therefore possibly reduces uterine blood flow.’ This conclusion is, on the face of it, unlikely, given the probability of some sympathetic blockade affecting the region. Moreover, there is no way such a conclusion can be drawn from this study. There were no controls who laboured without epidural analgesia. What the study showed were changes in uterine artery resistance in the course of labour and after delivery in women all of whom happened to receive epidurals.
When considering maternal changes that might affect fetal welfare for one reason or another, it is also important to assess the actual neonatal outcome. Having no controls the authors were in no position to do this, but fortunately many studies have been conducted in which the effect on neonatal outcome of neuraxial has been compared with other types of analgesia and no analgesia. Meta-analysis has demonstrated clear neonatal benefit associated with epidural analgesia in improving Apgar score2 and, more importantly, reducing metabolic acidosis,3 the latter even in comparison to no analgesia.4
It is crucially important that such spurious adverse findings do not get into the hands of the many who campaign to minimize epidural use in obstetrics, thereby depriving mother and baby of the benefits that we as anaesthetists quite fail to publicize.
Taipei, Taiwan
* E-mail: wzsun{at}ntu.edu.tw
Editor—We would like to thank Professor Reynolds for helping elucidate the controversy in our manuscript.1 First, we agree that an additional group of parturients who laboured without epidural analgesia is the ideal control group. However, the essence of our study design was to compare Doppler velocimetric variables between uterine contraction and relaxation. All paturients must be measured sequentially along different time points (1, 2, 4 h) after epidural infusion and post-delivery. Furthermore, we also noted Doppler velocimetric measurements comparable to our pre-epidural control in a non-epidural control of Bhushan and colleagues.5 Thus, we believe that the pre-epidural insertion data (time 0) in our study design could also serve as an appropriate control.
Secondly, Dr Reynolds has precisely pointed out the limitation in velocimetric measurements of uterine artery and potentially misleading interpretation in our discussion. As with most previous investigations, we used RI, S/D ratio and PI to measure uterine artery resistance. Neither uterine nor umbilical blood flow was measured. Thus, our evidence is insufficient to conclude that epidural analgesia with bupivacaine 0.075% reduced uterine blood flow through enhancing the resistance of uterine artery. To further elucidate the impact on fetal circulation, we recently measured the Doppler velocimetry of umbilical arteries throughout different periods of labour analgesia. Our preliminary data confirm that continuous epidural analgesia increased uterine blood resistance, but did not alter umbilical blood flow throughout the labour course regardless of uterine contraction or relaxation (in preparation). The lack of influence on the fetal circulation substantiates Reynolds' assertion that epidural analgesia is associated with better neonatal outcome than no analgesia.3
References
1 Chen LK, Lin CJ, Huang CH, et al. (2006) The effects of continuous epidural analgesia on Doppler velocimetry of uterine arteries during different periods of labour analgesia. Br J Anaesth 96:226–30.
2 Halpern SH, Leighton BL, Ohlsson A, Barrett JFR, Rice A. (1998) Effect of epidural vs parenteral opioid analgesia on the progress of labor. JAMA 280:2105–10.
3 Reynolds F, Sharma S, Seed PT. (2002) Analgesia in labour and funic acid- base balance: a meta-analysis comparing epidural with systemic opioid analgesia. Br J Obstet Gynaecol 109:1344–53.
4 Schocket M, Garrison R, Wiley J, Sharma S. (2005) Epidural analgesia has a favorable effect on funic base excess compared to no analgesia during labor. Anesthesiology 102: SOAP abstract A-40.
5 Bhushan NL and Shafeek AA. (1999) Doppler velocimetry of uterine and umbilical arteries during pregnancy. Ind J Radiol Imag 9:119–25.
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