The 90% Effective Dose of Intrathecal Hyperbaric Bupivacaine for Cesarean Delivery Under Combined Spinal-Epidural Anesthesia in Parturients With Super Obesity: An Up-Down Sequential Allocation Study

( Can J Anesth . 2024;71(5):570–578. doi:10.1007/s12630-024-02705-5) A greater number of obese parturients are giving birth through cesarean delivery (CD), in part due to rising rates of both obesity and CDs worldwide. To avoid various complications during a CD, the ideal option for anesthesia is a neuraxial technique, with either spinal or combined spinal-epidural (CSE) anesthesia. A sensory block at the T4 dermatome is achieved using intrathecal hyperbaric bupivacaine and opioids. Previous studies have reported the efficiency of intrathecal hyperbaric bupivacaine to be 95% when the dose is between 11 and 15 mg, however, these studies were performed mostly in patients who were not obese. In addition, magnetic resonance imaging has shown reduced levels of cerebrospinal fluid within the lumbar region, which has further been explained to cause excessive spread of the block cephalad. Thus, it has been suggested that reducing the dose of intrathecal bupivacaine within the obese population is essential to avoiding adverse effects across several systems of the body. However, various clinical trials contain data which suggest that this dosage reduction in obese woman is not necessary, although their data do not include individuals considered to be super obese (BMI ≥50 kg/m 2 ). Importantly, the dose of intrathecal bupivacaine should be high enough to create adequate surgical anesthesia, otherwise the use of general anesthesia may be employed, increasing the risk of morbidity. Since the field lacks a consensus on intrathecal hyperbaric bupivacaine dosage for patients with super obesity undergoing a CD under CSE, the authors sought clarification with this study. The hypothesized 90% effective dose (ED 90 ) was between 7.5 and 12 mg when administered with opioids.