Warming the epidural injectate improves first sacral segment block: a randomised double-blind study

This study investigated the effect of local anaesthetic temperature on block of the first sacral segment. Twenty-four patients undergoing lumbar epidural anaesthesia at L2-3 or L3-4 were randomly divided in double-blind fashion into two groups to receive 22 ml of lignocaine 2% with adrenaline 1:200,000, sodium bicarbonate and fentanyl, at either 21 degrees C (cold group) or 37 degrees C (warm group). The sensory block was assessed by loss of sensation to pinprick and the pain threshold after repeated electrical stimulation at L2, S1 and S3 dermatomes. Motor block was evaluated using the modified Bromage scale. Patient characteristics were comparable between the groups. Onset of block at the first sacral segment (S1) was faster in the warm group than in the cold (10 vs. 17.5 minutes, P < 0.001). The pain threshold at S1 was significantly higher in the warm group. We concluded that epidural lignocaine 2% with adrenaline 1:200,000, sodium bicarbonate and fentanyl injected at 370C hastens SI block within 10 minutes of administration.