Spinal anaesthesia with 0.5% bupivacaine 3 ml: comparison of plain and hyperbaric solutions administered to seated patients.

In a double-blind study, 0.5% bupivacaine 3 ml in plain (n = 10) or hyperbaric (n = 10) solution was injected intrathecally to 20 patients who were in the sitting position, to produce spinal anaesthesia for transurethral resection of prostate. No statistically significant differences were found in time to maximum cephalad spread of analgesia nor in the level reached. However, the plain solution produced a smaller scatter around the mean level than the hyperbaric solution. The duration of analgesia was not significantly different between two groups. There was no difference in the incidence of complete motor block, but a longer duration of lesser degrees of motor block was found with the plain solution (P less than 0.05). The plain solution produced a more predictable level of blockade.