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Intrathecal bupivacaine dose for cesarean delivery is not reduced in obese compared to non-obese parturients
Abstract Number: S-30
Abstract Type: Original Research
The optimal dose of local anesthetic for obese parturients undergoing spinal anesthesia for cesarean delivery (CD) is controversial due to concerns about exaggerated block spread with doses used in non-obese patients. Previous MRI studies have shown that obese patients have reduced lumbar cerebrospinal fluid volume, and that there is an inverse correlation between this reduced volume and the cephalad spread of neuraxial blockade (1,2). Other studies, however, examining the ED95 and ED50 of hyperbaric bupivacaine for CD in obese and non-obese patients do not seem to support concerns of high cephalad spread (3,4). The purpose of this study was to investigate the hypothesis that standard doses of hyperbaric bupivacaine for CD do not cause an increased risk of high spinal block in the obese parturient.
After IRB approval, we searched the perioperative database for women who underwent CD under spinal or combined spinal epidural anesthesia from 2003-2012. We included patients who received our standard doses of local anesthetic (1.4-1.6mL of 0.75% hyperbaric bupivacaine) with fentanyl 15mcg and morphine 0.1-0.2mg. Obesity was defined as BMI ≥ 30. Exaggerated cephalad block (high spinal) after initial spinal dose was the primary outcome. High spinal was defined as need to convert to general anesthesia within the first 20 minutes after initial block due to weakness, altered mentation or respiratory distress or recorded block height ≥ T1. Chi-square test was used to compare high spinal rate between obese and non-obese parturients. We also performed a multivariable regression analysis with high block as the outcome and age, height, weight, obesity, ethnicity, gestational age and hyperbaric bupivacaine dose as predictors.
4724 patients (1828 non-obese and 2896 obese) fulfilled the inclusion criteria and were included in the analysis. Except for higher weight and BMI in the obese group, there were no clinically significant differences between the groups in age, height, ethnicity, gestational age or dose of hyperbaric bupivacaine used. Overall, there were 28 high spinal blocks (0.6%) with no significant difference between obese and non-obese parturients (0.7% versus 0.4%, p=0.2). In two obese and one non-obese patient, general anesthesia was induced due to a high block. In the multivariable model, obesity was not a significant predictor of high block [adjusted odds ratio (95% confidence interval) = 1.1 (0.4-3.0)] nor was any of the other predictors.
At standard spinal doses of hyperbaric bupivacaine for CD, there is no significant difference between obese and non-obese patients in the risk of developing high spinal block. These findings confirm earlier ED95 and ED50 studies and suggest that spinal dose reductions are not required in this population.
1. Anesthesiology 1996; 84:1341-9
2. Anesthesiology 1998; 89:24-9
3. Rev Bras Anestesiol 2009; 59:674-83
4. Anesthesiology 2011; 114:529-35