F McDonagh, JCA Carvalho, S Abdulla et al.
Anaesthesia 2022, 77, 892–900. https://doi.org/10.1111/anae.15714
AIM OF STUDY
To compare effect of low- and high-dose carbetocin and low- and high-dose oxytocin on uterine tone intensity at elective C-section
DESIGN (& LOCATION)
Double-blinded randomised controlled non-inferiority trial at two centres in Ontario, Canada between May 2017 and Dec 2020
METHODOLOGY
Low risk elective c-sections were randomly allocated to 20mcg carbetocin, 100mcg carbetocin, 0.5 units oxytocin and infusion or 5 units oxytocin and infusion groups. Clinicians were blinded throughout. Uterine tone was assessed using a Verbal Numerical Rating Scale by the obstetrician at 2, 5 and 10 minutes after drug administration.
PRIMARY OUTCOME
Intensity of uterine tone on VNRS of 0-10 evaluated by obstetrician 2 minutes after administration of study drug
SECONDARY OUTCOMES
- Uterine tone VNRS at 5 and 10 minutes
- Use of additional uterotonics in operating theatres, and in first 24 hours post-op
- Adverse effects up to 2 hours after study drug injection
- Estimated blood loss
STATISTICS
95%CI for difference in the primary outcome between high- and low-dose groups was estimated using quantile regression
Non-inferiority implied if lower boundary of 95%CI of difference between groups was less than pre-determined margin of 1.2
Secondary outcomes compared using F-test for continuous variables, and Chi-squared for categorical variables
RESULTS
Lower boundary of 95% CI of difference between groups did not exceed non-inferiority margin of 1.2 for any of the study groups at 2, 5 or 10 minutes
CONCLUSIONS/DISCUSSION
20 mcg carbetocin was non-inferior to 100 mcg carbetocin and 5 IU oxytocin for primary and secondary outcomes of uterine tone intensity at 2, 5 and 10 minutes, and 0.5 IU oxytocin was non-inferior to 100 mcg carbetocin and 5 IU oxytocin for these outcomes
Low- and high-dose regimens for both drugs were associated with similar need for further uterotonics, bloods loss and adverse effects
STATED LIMITATIONS FROM STUDY
Subjective method of uterine tone assessment
Method of blood loss estimation based entirely on change in haematocrit
DISCUSSION FROM JOURNAL CLUB MEETING (? Change of practice)
Study does not provide a basis from which to change practice, but adds to weight of evidence favouring lower doses of both carbetocin and oxytocin within the defined population studied, and to the evidence of non-inferiority of carbetocin to oxytocin
The ED90 of both drugs is known to be significantly higher in obese patients who were excluded from this study, as where patients at increased risk of post-partum haemorrhage, limiting the applicability of the low dose regimens to wider practice
The need for consensus with obstetric colleagues when deciding on uterotonic doses has also limited use of lower doses in the past and their involvement will be important if changing practice.
Summary by Dr D Bailey. Journal Club Meeting 10th November 2022.
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