THE EFFECT OF CEREBROSPINAL-FLUID DILUTION OF ISOBARIC 0.5-PERCENT BUPIVACAINE USED FOR SPINAL-ANESTHESIA

A prospective study was conducted to see the effect on spinal anaesthe sia of the dilution of isobaric 0.5% bupivacaine with cerebrospinal fl uid. Sixty patients were randomly allocated to three groups. In group 1, patients received 3 ml isobaric 0.5% bupivacaine intrathecally with out cerebrospinal fluid. In groups 2 and 3, cerebrospinal fluid 1 ml a nd 2 ml was aspirated respectively and mixed with 3 ml isobaric 0.5% b upivacaine. A total volume of 4 ml in group 2 and 5 ml in group 3 was administered. Thus, the volume of cerebrospinal fluid remained unchang ed. Pinprick analgesia and motor block was evaluated from induction un til recovery. No differences in onset time, duration and 'two segments regression' were noticed. The only statistical difference was the tim e to reach complete motor block, which was shorter in group 1 as compa red to group 2 and 3 (6.9 SD 1.4 min versus 11.3 SD 3.0 and 13.5 SD 3. 9 min respectively). The mean value of maximum decrease in systolic bl ood pressure was small, being less than 15% of the pre-operative value for each group. In conclusion, the effect of diluting isobaric 0.5% b upivacaine with cerebrospinal fluid, 1 ml and 2 ml, is minimal and it is an unnecessary procedure with limited clinical effect.