Influence of the lumbar interspace chosen for injection on the spread of hyperbaric 0.5% bupivacaine.

Forty patients undergoing elective Caesarean section were allocated randomly to receive hyperbaric 0.5% bupivacaine 2.5 ml at either the L2-3 (n = 20) or L4-5 (n = 20) interspace. Spinal injection was performed with a 29-gauge needle in 38 patients and a 25-gauge needle in two. The onset time to analgesia at T10 and T6 was significantly faster and the level of analgesia at 5 and 10 min after injection significantly higher after injection at L2-3. Maximum height and range of analgesia, the level of analgesia at 15 and 20 min after injection and the number of episodes of hypotension were not significantly different between the two groups. One case of post-dural puncture headache was recorded after use of a 29-gauge needle. Overall, the choice of lumbar interspace influenced the rate of onset of analgesia, but not the final dermatomal level (mean and range) of analgesia achieved.