BACKGROUND
Volatile anaesthesia may increase blood loss because of the uterine-relaxing effect of the volatile anaesthetics during caesarean section under general anaesthesia.
RESULTS
We identified 26 585 women, including 19 320 in the volatile anaesthesia group (mean age = 32.9 ± 5.5 years) and 7265 in the TIVA group (mean age = 32.8 ± 5.5 years). The mean blood loss was 1113 ± 909 and 1136 ± 944 ml and the proportion of blood transfusion was 14.7 and 16.0% in the volatile and TIVA groups, respectively. With conventional regression analyses, volatile anaesthesia was associated with a slightly lower risk of bleeding: the adjusted mean difference for blood loss (95% CI) was −56.1 (−81.4 to −30.7). However, in the instrumental variable analysis, volatile anaesthesia was associated with a higher risk of bleeding: adjusted mean difference for blood loss (95% CI) was 154.3 (112.4 to 196.3) ml.
CONCLUSION
This large observational study with instrumental variable analyses suggested an increased bleeding risk associated with volatile anaesthesia, and the results were not identical to those in the conventional regression analyses.
KEY POINTS
- Is volatile anaesthesia associated with an increase in caesarean section bleeding because of its uterine-relaxing effect?
- In the conventional regression analyses, the volume of blood loss and proportion of blood transfusion were slightly lower in the volatile anaesthesia group than in the total intravenous anaesthesia group; however, the instrumental variable analyses showed that volatile anaesthesia was associated with an increased risk of bleeding.
- Using a nationwide observational database in Japan, our instrumental variable analyses suggested an association between volatile anaesthesia and increased risk of caesarean section bleeding, which is in line with its physiological mechanism of uterine relaxation.