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Sir,

We read with interest the study by Jonsson et al.1 and wish to comment on the authors’ conclusions.

The authors correctly state in the introduction that the cardiovascular side effects of oxytocin are dose-related. However, the use of 5 iu oxytocin is recommended for patients undergoing caesarean delivery by a number of regulatory societies (National Collaborating Centre for Women’s and Children’s Health; National Institute for Health and Clinical Excellence; and the Royal College of Obstetricians and Gynaecologists).2 Further explanation is needed to justify the use of 10 iu oxytocin in this study, as Butwick et al. and Carvalho et al.3,4 have shown that oxytocin doses of less than 5 iu are effective in achieving adequate uterine tone during elective caesarean delivery.

The interim analysis indicated a high prevalence of ST depression (24%) in patients receiving 10 iu oxytocin. Why was the study not stopped at this time because of the observed adverse effects associated with this higher dose? In addition, the authors provide limited statistical data to validate their recruitment of an additional 50 patients following interim analysis. Their results indicate that the differences in proportion of patients with ST depression associated with oxytocin bolus between groups only barely met the criteria for statistical significance (P = 0.046).

Tachycardic responses resulting from the anticholinergic effects of atropine may have contributed to ST changes. Atropine use was relatively high in each group; however, no information of the timing of atropine administration is provided. Furthermore, the use of additional oxytocin doses and other uterotonics (in the 5-iu oxytocin group) also limits direct comparisons of ST changes between 5 and 10 iu oxytocin.

Peak effects on ST changes may have occurred earlier than reported in the study, as Dyer et al. and Svanstrom et al.5,6 have shown that peak peripheral vascular effects and electrocardiogram (ECG) changes are observed within 60 seconds of the administration of oxytocin.

Despite these apparent limitations, this study adds to current evidence supporting the use of a bolus of ≤5 iu oxytocin during elective caesarean delivery, so as to minimise cardiovascular oxytocin-related side effects. Future work should focus on investigating optimal oxytocin infusions for the maintenance of adequate uterine tone following oxytocin bolus administration. We question whether there is relevant scientific justification for further investigations of the administration of >5 iu oxytocin for patients undergoing elective caesarean delivery.

References

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  2. References
  • 1
    Jonsson M, Hanson U, Lidell C, Norden-Lindeberg S. ST depression at caesarean section and the relation to oxytocin dose. A randomised controlled trial. BJOG 2010;117:7683.
  • 2
    Wedisinghe L, Macleod M, Murphy DJ. Use of oxytocin to prevent haemorrhage at caesarean section--a survey of practice in the United Kingdom. Eur J Obstet Gynecol Reprod Biol 2008;137:2730.
  • 3
    Butwick AJ, Coleman L, Cohen SE, Riley ET, Carvalho B. Minimum effective bolus dose of oxytocin during elective Caesarean delivery. Br J Anaesth 2010;104:33843.
  • 4
    Carvalho JC, Balki M, Kingdom J, Windrim R. Oxytocin requirements at elective cesarean delivery: a dose-finding study. Obstet Gynecol 2004;104:100510.
  • 5
    Dyer RA, Reed AR, van Dyk D, Arcache MJ, Hodges O, Lombard CJ, et al. Hemodynamic effects of ephedrine, phenylephrine, and the coadministration of phenylephrine with oxytocin during spinal anesthesia for elective cesarean delivery. Anesthesiology 2009;111:75365.
  • 6
    Svanstrom MC, Biber B, Hanes M, Johansson G, Naslund U, Balfors EM. Signs of myocardial ischaemia after injection of oxytocin: a randomized double-blind comparison of oxytocin and methylergometrine during Caesarean section. Br J Anaesth 2008;100:6839.