Spinal analgesia using bupivacaine 0.5% plain. Variation in the extent of the block with patient age.

Bupivacaine 0.5% plain solution was used to produce spinal analgesia on 63 occasions. In 33 patients a fixed dose of 4 ml injected at the L2/3 interspace at 0.5 ml/second produced an extent of analgesia which was directly related to patient age (p les than 0.005). The latency was 17.3 minutes (SD 8 . 4) and duration of action was 286 minutes (SD 62). A second group receiving only 1 ml of solution had a much shorter duration of action (mean 154 minutes, SD 30). In 90% of patients the analgesia obtained was fully sufficient for surgery to be performed and no form of analgesic supplementation was given. On two occasions no analgesia occurred at all. Bupivacaine 0.5% plain proved to be an effective agent for subarachnoid block. The extent of analgesia was, however, poorly predictable, and even with low doses unacceptably high level of block were sometimes achieved.