Caudal analgesia for perianal surgery. A comparison between bupivacaine and diamorphine.

Seventy-three patients undergoing elective perianal surgery were randomly divided into a control group, a group who received a caudal injection of 20 ml bupivacaine 0.5% plain and a group who received diamorphine 2.5 mg in 10 ml normal saline by caudal injection; a comparison was then made of postoperative analgesia requirements. The bupivacaine group had better analgesia than the control group for the first 8 hours, after which there was no difference. The diamorphine group had better analgesia than the control group for the first 24 hours postoperatively. Side effects were less in the diamorphine group than the control, or the bupivacaine group. In particular, 41% of the bupivacaine group complained of some degree of urinary retention and one patient required temporary catheterisation. It is concluded that caudal diamorphine gives good postoperative analgesia for perianal operations, particularly when motor blockade is not wanted by the surgeon.