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Comparison of Isobaric and Hyperbaric Bupivacaine for Spinal Anesthesia in Patients Undergoing Postpartum Bilateral Tubal Ligation
Abstract Number: T2D-354
Abstract Type: Original Research
Background: Hyperbaric (HB) and isobaric (IB) bupivacaine have been used for spinal anesthesia in obstetric surgery. Past studies do not demonstrate superiority of one formulation over the other . The purpose of this retrospective study is to evaluate the efficacy and failure rates of spinal anesthesia with hyperbaric (0.75%) versus isobaric (0.5%) bupivacaine in patients undergoing postpartum bilateral tubal ligation (BTL).
Methods: The records of 100 HB and 100 IB patients who received postpartum BTL between June 2017 to August 2018 were collected. Demographics, spinal anesthetic variables, supplemental anesthetic medications, and conversion to general anesthesia were compared. Spinals were performed with the patient in the sitting position and followed by the supine position after injection. As per standard practice at our institution, 20mcg of fentanyl was added to the bupivacaine.
Results: There was no difference in patient demographics between the HB and IB groups (Table 1). Median dose of HB was 10mg and IB was 10.5mg with a range of 5 - 21mg. Patients receiving IB were more likely to receive supplemental medications such as fentanyl (40% HB vs 66% IB, p < 0.05), midazolam (84% HB vs 98% IB, p < 0.05), and propofol (4% HB vs 11% IB, p < 0.05). Rate of conversion to general anesthesia, constituting a failed spinal block, tended to be higher in patients receiving IB (4% HB vs 9% IB, p = 0.076).
Conclusion: The results showed that IB bupivacaine had an increased need for supplemental anesthetics despite similar doses of bupivacaine used in each group. This finding suggests IB bupivacaine is less effective than HB bupivacaine for tubal ligation procedure. There may also be an increased risk of failure with need for conversation to general anesthesia with IB bupivacaine. Possible explanations for these findings include differences in the density of block, rise of the block due to baricity, and operator unfamiliarity with IB dosing. 
 Sng BL, Siddiqui FJ, Leong WL, et al. Hyperbaric versus isobaric bupivacaine for spinal anaesthesia for caesarean section. Cochrane Database Syst Rev. 2016;9:CD005143.
 Uppal V, Retter S, Shanthanna H, et al. Hyperbaric Versus Isobaric Bupivacaine for Spinal Anesthesia: Systematic Review and Meta-analysis for Adult Patients Undergoing Noncesarean Delivery Surgery. Anesth Analg. 2017;125(5):1627-1637
 Beecroft, Christina. Spinal anaesthesia. Anaesth Intensive Care. 2015;16(11):563-565