Introduction: Postpartum haemorrhage is the leading cause of worldwide maternal morbidity and mortality. The most frequent cause for its occurrence (90 % of cases) is uterine atony or disfunctional uterine contraction. Carbetocin is an oxytocin receptor agonist, latest studies have shown its noninferiority, some even superiority in efficiency compared to the recommended uterotonic oxytocin. Electrohysterography is an objective, noninvasive method for monitoring uterine activity dinamics, it was extensively used in research of pregnancy and labour. Until now there is no known study estimating uterotonic efficiency on the postpartal contracting uterus using electrohysterography. The aim of our study was to compare changes in postpartum electrohysterogram in women after caesarean section after preventive uterotonic application, either oxytocin or carbetocin.
Methods: In our single center randomised study 64 healthy women with singleton pregnancy at term (⡥ 37 weeks of gestation) scheduled for caesarean section after a previous caesarean section were included. After the procedure, a blood sample was obtained for laboratory analysis (haemogram) and a 15-minute electrohysterogram was recorded. Women were randomised in two groups: the first received a single dose of 100 μg of carbetocin (Pabal®) intravenously, the second received 5 IU of oxytocin (Syntocinon®) intravenously. After uterotonic application a 30-minute electrohysterogram was obtained, followed by a third electrohysterogram two hours after therapy administration. While recording each electrohysterogram, we asked women to assess their pain using a visual analogue scale. Electrohysterograms were obtained using two pairs of bipolar electrodes placed on the abdominal wall, with a custom-made recording machine. On the electrohysterograms we visually identified burst like contractile elements (»pseudo bursts«). Each contractile element was analysed via Fourier transformation and a power density spectrum integral was obtained. We analysed the mean value of power density spectrum peak frequency, the mean value of power density spectrum peak amplitude, the frequency and duration of pseudo bursts.
Results: The change in power density spectrum peak frequency (from admission to two hours after uterotonic application) was statistically significantly lower in the oxytocin group compared to carbetocin (Median of change = 0,07 Hz (Interquartile range: 0,87 Hz) compared to Median of change = – 0,63 Hz (Interquartile range: 0.20 Hz); p = 0,004, Wilcoxon signed-rank test). A statistically significant difference was seen in power density spectrum peak frequency two hours after uterotonic, an increase was recorded in the oxytocin and a decrease in the carbetocin group (Median = 0,43 Hz (Interquartile range: 0,12 Hz) compared to Median = 0,39 Hz (Interquartile range: 0,08 Hz); p = 0,030, Mann-Whitney U test). No statistically significant differences were observed in other parameters. A statistically significant difference in change of haemoglobin and haematocrit 24 hours after caesarean section was not obtained. There were no statystically significant differences in assessment of pain using the visual analogue scale between the two groups, while similar unwanted effects were noted.
Conclusions: We found a significantly higher electrohysterographic parameter power density spectrum peak frequency two hours after oxytocin, compared to carbetocin application. Postpartal electrohysterography could represent an additional objective tool for uterotonic efficiency estimation.
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