Background: Early utilisation of neuraxial anaesthesia has been recommended to reduce the need for general\nanaesthesia in obese parturients. The insertion and management of labour epidurals in obese women is not\nstraight-forward. The aim of this pilot study was to compare the failure rate of extension of epidural analgesia for\nemergency caesarean section, in pregnant women with a body mass index (BMI) ââ?°Â¥ 40 kg/m2, to those with a\nBMI < 30 kg/m2. The results will be used to calculate the sample size of a planned prospective study.\nMethods: In this retrospective, (1:1) caseââ?¬â??control pilot study, obese subjects and control subjects were selected\nfrom the obstetric database, if they delivered between January 2007 and December 2011. All subjects used epidural\nanalgesia during labour and subsequently required anaesthesia for Category 1 or 2 Caesarean Section. Data was\nextracted from the patient medical record. Failure to extend was analysed using liberal and restrictive definitions.\nChi-square or Fisherââ?¬â?¢s exact tests were used to detect differences between groups. Multiple logistic regression was\nused to examine variables predictive of extension failure.\nResults: There were 63 subjects in each group. The mean BMI of the obese group was 45.4 (5.8) kg/m2 and 23.9\n(3.0) kg/m2 in the control group. The odds ratio for failure to extend the existing epidural blockade (liberal\ndefinition) was 2.48 (95 % CI:1.02 ââ?¬â?? 6.03) for the obese group compared with the control group (adjusted for age,\nparity and gestation). Using the restrictive definition, the odds ratio for failure in the obese group was 6.78 (95 %\nCI:1.43 ââ?¬â?? 32.2). The combination of respiratory co-morbidity and gestational diabetes significantly predicted\nextension failure. Surgical time and epidural complications on labour ward were significantly greater in the obese\ngroup.\nConclusions: In this small retrospective cohort, patients with a BMI ââ?°Â¥ 40 kg/m2 were significantly more likely to fail\nepidural extension for caesarean section. The presence of respiratory co-morbidity and gestational diabetes were\nsignificant predictors of extension failure; their clinical relevance requires further evaluation.
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