Effects of baricity and mass of bupivacaine solutions in spinal anesthesia

We studied the effects of three different solutions of bupivacaine, injected intrathecally. Each solution had a volume of 3 ml and differed from the others by its mass or its baricity. Sixty-five patients, divided into three groups, remained in the sitting position for one minute after injection of the tested solutions. Group 1 received 10 mg of hyperbaric bupivacaine, group 2 received 10 mg of isobaric bupivacaine and group 3 received 15 mg of isobaric bupivacaine. Groups 1 and 2 showed no statistical difference in maximal extension of analgesia (T 11 and T 10), nor in mean duration of analgesia (155 and 159 min.). The motor block was similar in both groups (score less than 2 using the Bromage scale 0-3). Group 3 had a higher level of maximal cephalad extension and a longer mean duration of analgesia (186 min.). The motor block was more pronounced after 30 min. (85% score 3) compared to the two other groups. The decrease in mean arterial pressure was moderate and similar in the three groups. In view of the results of this study, we suggest the use of 3 ml of 0.5% isobaric bupivacaine injected intrathecally.