What is the failure rate in extending labour analgesia in patients with a body mass index ≥ 40 kg/m2compared with patients with a body mass index < 30 kg/m2? a retrospective pilot study

Abstract

BackgroundEarly 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/m2, to those with a BMI < 30 kg/m2. The results will be used to calculate the sample size of a planned prospective study.MethodsIn 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.ResultsThere were 63 subjects in each group. The mean BMI of the obese group was 45.4 (5.8) kg/m2 and 23.9 (3.0) kg/m2 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.ConclusionsIn this small retrospective cohort, patients with a BMI ≥ 40 kg/m2 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.

Does obesity complicate regional anesthesia and result in longer decision to delivery time for emergency cesarean section?

“…The failure rates of epidural top‐up have been shown to be greater compared to spinal anesthesia for cesarean delivery . Maternal obesity has been shown to increase the likelihood of failed epidural top‐up while single shot spinal anesthesia following an epidural top‐up may lead to extremely high spinal blocks …”

Epidural extension failure in obese women is comparable to that of non‐obese women

“…The effectiveness of epidural extension in obese women is important to know, as epidurals may be placed with the explicit intention of permitting extension for subsequent cesarean delivery if required 9, 10. Our previous retrospective pilot study found epidural extension was more likely to fail in women with BMI ≥ 40 kg/m 2 11. This study used a prospective cohort at two centers to validate that result.…”

“…We believe that this definition is pragmatic and reduces the influence of investigator bias. The extension failure rate used in the sample size calculation was also based on this definition 11. The non‐significant result may be due to a lower epidural extension failure rate found in the obese group, than was observed in the pilot study, with subsequent under‐powering of this study.…”

“…This liberal definition of extension failure was used in our pilot study11 and has been used previously 15. Regional anesthesia (RA) was defined as epidural extension or a new neuraxial technique being successfully used for the duration of surgery.…”

“…Based on a failure rate of 15.9%11 in the control group and using 2 : 1 matching of controls to participants, it was calculated that 100 obese participants and 200 control participants would detect an OR of at least 2.27 (α = 0.05 and β = 0.2). SPSS Version 22 was used for statistical analyses.…”