Correlation of bupivacaine 0.5% dose and conversion from spinal anesthesia to general anesthesia in cesarean sections

Failed spinal anesthesia for cesarean sections may require conversion to general anesthesia. The aim of this study was to determine whether the administered spinal bupivacaine dose for performing a cesarean section under spinal anesthesia was related to the conversion rate to general anesthesia. Retrospective analysis was performed on 1252 electronic data and file of patients who underwent a cesarean section under spinal anesthesia between 2004 and 2011. In 15 patients, spinal anesthesia was converted into general anesthesia due to block failure. Patients in whom a bupivacaine dose of 8 mg or smaller was administered had significantly higher conversion rate (3/61 (4.9%) patients and 12/1191 (1.0%) patients, respectively; p < 0.05.). The relative risk of conversion with a 8 mg dose or lower is 4.88 (95% CI 1.41 - 16.85). This retrospective study shows that a low dose administration a bupivacaine 0.5% for spinal anesthesia in cesarean section patients elicits significantly more frequent conversion to general anesthesia.