Conversion of epidural labour analgesia to anaesthesia for Caesarean section: a prospective study of the incidence and determinants of failure

Background. The incidence of general anaesthesia (GA) has been used as a marker for the quality of obstetric anaesthesia care. Recent guidelines suggest the rate of GA for Caesarean section in parturients with pre-existing epidural analgesia for labour should be <3%. The primary purpose of this study is to determine whether or not this is an achievable standard in a university teaching hospital. We also wished to determine the factors influencing the incidence of inadequate anaesthesia. Methods. We studied a consecutive cohort of 501 patients who had a Caesarean section after epidural labour analgesia. The incidence of GA, the total incidence of failure, and the factors previously associated with failure were recorded. Factors shown to be significant with univariate analysis were used in a binary logistic regression to determine the independent risk factors for failure. Results. Twenty-one of 501 parturients required GA (4.1%, 95% confidence interval 2.6-6.3%), not significantly different from 3% (P=0.1). Fifteen of 21 (71%) of these occurred intraoperatively. The total rate of failure was 30/501 (5.9%, 95% confidence interval 4.0-8.4%). Maternal height and the number of clinician top-ups in labour were the significant independent risk factors for failure. Conclusions. Intraoperative conversion to GA may increase both maternal and fetal risks. Strategies to reduce the incidence may include early recognition of inadequate labour analgesia and reliable assessment of adequacy of surgical anaesthesia.