BJA Advance Access originally published online on November 25, 2005
British Journal of Anaesthesia 2006 96(1):106-110; doi:10.1093/bja/aei284
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Obese parturients have lower epidural local anaesthetic requirements for analgesia in labour
1 Division of Women's Anesthesia, Department of Anesthesiology, Duke University Medical Centre, Durham, NC 27710, USA. 2 Department of Anaesthesia, South Manchester University Hospital, Wythenshawe M23 9LT, UK
* Corresponding author: Department of Anesthesiology, University of Texas HSC Houston Medical School, 6431 Fannin St, Suite 5.020, Houston TX 77030, USA. Email: Moeen.K.Panni{at}uth.tmc.edu
Background. There are no studies comparing local anaesthetic requirements for obese and normal parturients. Obesity has been associated with a higher incidence of Caesarean section and higher levels of epidural block have also been found in obese obstetric patients, suggesting they may require less local anaesthetic. The aim of our study was to estimate the minimum local analgesic concentration (MLAC) of bupivacaine for obese and non-obese parturients.
Methods. Otherwise healthy parturients (n=32) requesting epidural analgesia were enrolled in this up–down sequential allocation study. Women were in active labour (3–6 cm cervical dilatation) with visual analogue pain scores (VAPS) >40/100 mm. Subjects with BMI >30 kg m–2 were allocated to the obese group and BMI 
30 kg m–2 were allocated to the normal group. The initial epidural dose for both groups was 20 ml 0.1% w/v bupivacaine (20 mg), with a dosing increment of 0.01% w/v VAPS 10/100 mm defined effective analgesia. The MLAC was estimated using up–down reversals and probit regression with P<0.05 as significant.
Results. Groups were similar except for BMI and weight (P<0.001). Local anaesthetic requirements were significantly (P<0.001) reduced by a factor of 1.68 (95% CI 1.32–2.29) in the obese group, with significantly higher initial level of block (P<0.001).
Conclusion. We found obese parturients to have significantly decreased epidural bupivacaine analgesic requirements. A contributing factor to obese patients having more difficult labours may be that relatively larger doses of local anaesthetic are administered than actually required. It may be worth considering lowering the concentrations and doses with which we initiate analgesia in obese parturients.
This work has been presented in abstract form only, at the annual meeting of the Society for Obstetric Anesthesiology, Palm Springs, CA, USA, May 4–7, 2005.
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