What is the failure rate in extending labour analgesia in patients with a body mass index ≥ 40 kg/m(2)compared with patients with a body mass index < 30 kg/m(2)? a retrospective pilot study

BACKGROUND: Early utilisation of neuraxial anaesthesia has been recommended to reduce the need for general anaesthesia in obese parturients. The insertion and management of labour epidurals in obese women is not straight-forward. The aim of this pilot study was to compare the failure rate of extension of epidural analgesia for emergency caesarean section, in pregnant women with a body mass index (BMI) ≥ 40 kg/m(2), to those with a BMI < 30 kg/m(2). The results will be used to calculate the sample size of a planned prospective study. METHODS: In this retrospective, (1:1) case–control pilot study, obese subjects and control subjects were selected from the obstetric database, if they delivered between January 2007 and December 2011. All subjects used epidural analgesia during labour and subsequently required anaesthesia for Category 1 or 2 Caesarean Section. Data was extracted from the patient medical record. Failure to extend was analysed using liberal and restrictive definitions. Chi-square or Fisher’s exact tests were used to detect differences between groups. Multiple logistic regression was used to examine variables predictive of extension failure. RESULTS: There were 63 subjects in each group. The mean BMI of the obese group was 45.4 (5.8) kg/m(2) and 23.9 (3.0) kg/m(2) in the control group. The odds ratio for failure to extend the existing epidural blockade (liberal definition) was 2.48 (95 % CI:1.02 – 6.03) for the obese group compared with the control group (adjusted for age, parity and gestation). Using the restrictive definition, the odds ratio for failure in the obese group was 6.78 (95 % CI:1.43 – 32.2). The combination of respiratory co-morbidity and gestational diabetes significantly predicted extension failure. Surgical time and epidural complications on labour ward were significantly greater in the obese group. CONCLUSIONS: In this small retrospective cohort, patients with a BMI ≥ 40 kg/m(2) were significantly more likely to fail epidural extension for caesarean section. The presence of respiratory co-morbidity and gestational diabetes were significant predictors of extension failure; their clinical relevance requires further evaluation.