Spinal anaesthesia with hyperbaric bupivacaine: effects of concentration and volume when administered in the sitting position.

In a double blind study, solutions of 0.5% or 0.75% bupivacaine containing 8% dextrose were compared with regard to the effect of varying concentration and volume when administered intrathecally to patients in the sitting position. Ten patients received 3 or 4 ml of 0.5% bupivacaine or 2 or 3 ml of 0.75% bupivacaine. Nine patients received 0.5% bupivacaine 2 ml and another nine received 0.75% bupivacaine 1.3 ml. The use of the 10-mg dose of both solutions was abandoned after nine patients in each group because of insufficient cephalad spread. With both solutions, the smallest volumes (bupivacaine 10 mg) had significantly shorter durations of action than both the larger ones (15-20/22.5 mg), between which there were no significant differences.