The effect of extradural ketamine on onset time and sensory block in extradural anaesthesia with bupivacaine

In a randomised, double blind study of 30 patients, we have compared two regimens for extradural anaesthesia: 20 ml bupivacaine 0.5%, 25 mg (0.5 ml) ketamine, 1 in 200,000 adrenaline; and 20 ml bupivacaine 0.5%, 0.5 ml 0.9% saline, 1 in 200,000 adrenaline. The main outcome measures were onset time to acceptable bilateral anaesthesia and postoperative analgesic duration. The time to onset of anaesthesia was reduced by 8 min in the bupivacaine-ketamine group compared with the bupivacaine alone group. In addition, the anaesthetic levels were two segments higher in the bupivacaine-ketamine group (T7 versus T9). Side effects were similar in both groups and there was no significant difference in postoperative analgesic requirements between the two groups. The addition of ketamine to bupivacaine given epidurally appears to be useful in the reduction of onset time to blockade.