Effect of epidural volume extension on dose requirement of intrathecal hyperbaric bupivacaine at Caesarean section

Background. The technique of epidural volume extension (EVE) involves the injection of saline into the extradural space immediately following the intrathecal injection, as part of a combined spinal-epidural (CSE) anaesthetic. One of the suggested benefits of EVE is a reduction in local anaesthetic required. The aim of this study was to test this hypothesis by comparing the median effective doses (ED50) of hyperbaric bupivacaine with fentanyl 25 mg with and without EVE for Caesarean section. Methods. Sixty women were randomized to receive either CSE anaesthesia with EVE (EVE group) or no EVE (NEVE group). Using a double-blinded, up-down sequential technique, varying doses of bupivacaine with fentanyl 25 mu g were administered. ED50 was estimated from up-down reversals and probit regression. Results. The ED50 for bupivacaine was similar and not significantly different in the two groups (5.1 mg in the EVE and 6.1 mg in the NEVE group; difference 1.0 mg, 95% CI-0.12 to 2.2, P = 0.08). Conclusions. This study illustrates that whilst low doses of intrathecal bupivacaine can be effectively used for Caesarean section, at such doses EVE does not appear to offer reliable or clinically relevant reductions in dosing with intrathecal bupivacaine.