Intrathecal Dosing for Cesarean Delivery in Obese and Nonobese Patients

To the editor: It has been proposed that the intrathecal dose of hyperbaric bupivacaine for spinal anesthesia should be reduced in morbidly obese patients undergoing cesarean delivery. This recommendation is consistent with the lower volume of cerebrospinal fluid observed in patients with high body mass index, but a lack of definitive evidence has been noted. Previously, Ginosar et al. reported the ED50 of intrathecal bupivacaine obtained in a prospective, randomized, doubleblind, and dose-finding study of healthy patients having elective cesarean delivery. Using the same experimental methods, Carvalho et al. repeated this experiment about 5 yr later at the same institution in patients with a body mass index of 40 or greater. Combining the data from the two studies on the success of the spinal block for operation, they used a quantal sigmoid Emax parametrization of the logistic model with nonlinear mixed effect model estimation using the NONMEM package (NONMEM version V [GloboMaxTM, Hanover, MD]),