Spread of spinal anaesthesia with plain 0.5% bupivacaine: influence of the vertebral interspace used for injection.

Three millilitre of plain 0.5% bupivacaine was injected intrathecally at two different levels in two groups of 20 patients. Injection at the L2/3 space produced a significantly higher spread of analgesia (mean T7 (SD 3.9)) than injection at L4/5 (T11(1.8)). The range of the cephalad spread of the block was less in the L4/5 group (P less than 0.001 at 60 min). The spread of anaesthesia continued beyond 30 min in both groups. In all patients anaesthesia sufficient for surgery of the knee and the foot was achieved. One patient had a final block level of T1 after injection at L2/3, accompanied by transient arterial hypotension.