The impact of body mass index on the risk of high spinal block in parturients undergoing cesarean delivery: a retrospective cohort study.

Abstract

To investigate the hypothesis that the risk of high spinal block is not increased in obese parturients undergoing cesarean delivery compared to non-obese parturients. This is a retrospective study at an academic center. We searched the perioperative database for women who underwent cesarean delivery under spinal or combined spinal epidural anesthesia with hyperbaric bupivacaine ≥10.5mg. A body mass index (BMI) ≥30kg/m2 was defined as obese. We categorized obesity into: obesity class I (BMI=30-34.9kg/m2), obesity class II (BMI=35-39.9kg/m2), obesity class III (BMI=40-49.9kg/m2), and super obese (BMI ≥50kg/m2). The primary outcome was high spinal block defined as need to convert to general anesthesia within 20min of spinal placement as a result of altered mental status, weakness, or respiratory distress resulting from the high block, or a recorded block height ≥T1. The analysis included 5015 women. High spinal blocks occurred in 29 patients (0.6%). The risk of high spinal was significantly different according to BMI (p=0.025). In a multivariate model, BMI (p=0.008) and cesarean delivery priority (p=0.009) were associated with high blocks. BMI ≥50kg/m2 was associated with greater odds of high block compared to BMI <30kg/m2 [odds ratio (95% confidence interval): 6.3 (2.2, 18.5)]. Scheduled cesarean delivery was also associated with greater odds of high block compared with unscheduled delivery. At standard spinal doses of hyperbaric bupivacaine used in our practice (≥10.5mg), there were greater odds of high block in those with BMI ≥50kg/m2.