The standard spinal preparation of bupivacaine contains a high concentration of glucose (80 mg ml). However, the addition of only a small amount of glucose (8 mg ml) to plain solutions of bupivacaine results in a solution which, although no more than marginally hyperbaric, produces a more predictable block when used for spinal anaesthesia in non-pregnant patients. However, bupivacaine 5 mg ml in glucose 8 mg ml has a density [1.00164 (SD 0.00008) at 37°C] which is relatively greater than that of the cerebrospinal fluid (CSF) of the pregnant patient at term (1.0003 at 37°C) because CSF density decreases during pregnancy. Therefore, a double-blind, randomized, controlled study was carried out to compare intrathecal bupivacaine (glucose 8 mg ml) with bupivacaine (glucose 80 mg ml) in 40 pregnant patients at term. Although there was no difference between groups in onset of sensory block, dose of ephedrine or patient satisfaction, patients receiving bupivacaine (5 mg ml) with glucose (8 mg ml) had persistently higher sensory blocks between 60 and 120 min after intrathecal injection, suggesting that the spread of spinal solutions in the pregnant patient at term is not dependent on density.
Connolly, C., McLeod, G. A., & Wildsmith, J. A. W. (2001). Spinal anaesthesia for Caesarean section with bupivacaine 5 mg ml–1 in glucose 8 or 80 mg ml–1. British Journal of Anaesthesia, 86(6), 805-807. https://doi.org/10.1093/bja/86.6.805