Spinal anaesthesia with hyperbaric bupivacaine: effects of concentration and volume administered

A double-blind study was carried out using hyperbaric solutions of bupivacaine to compare the effects of varying the concentration of bupivacaine and the volume of solution administered intrathecally. Fifty-seven patients were studied. Ten patients received each volume of each concentration: 0.5% bupivacaine in 8% dextrose, 2 ml, 3 ml or 4 ml and 0.75% bupivacaine in 8% dextrose, 1.3 ml or 2 ml. A further seven patients received 3 ml of the 0.75% solution. Both solutions consistently produced good nerve blockade. With the 0.5% solution, increases in the volume administered had no effect on the spread of sensory loss, whereas with the 0.75% solution, increasing the volume administered resulted in a significantly greater cephalad spread. The use of 3 ml of this solution was abandoned after seven patients had received it because of the excessive spread. With both solutions, increasing the volume produced a longer duration of action. The use of a 0.75% solution of hyperbaric bupivacaine for spinal anaesthesia did not appear to confer any advantage over the 0.5% solution.