Effect of diluent volume on post-operative analgesia and sedation produced by epidurally administered midazolam

We have studied the optimal diluent volume for post-operative analgesia and sedation produced by epidurally administered midazolam after upper abdominal surgery. Sixty patients were randomly allocated to four groups of 15 patients. When patients complained of pain after surgery, epidural midazolam 0.05 mg kg-1 in 3 mL saline (Group A), in 5 mL saline (Group B), in 10 mL saline (Group C) or in 15 mL saline (Group D) were injected as a bolus. The sedation was better and lasted longer in groups B and C than in the other two groups. Groups B and C also had significantly more extensive areas of analgesia than groups A and D from 30 min after the administration of midazolam. The interval to the second request for an analgesic was significantly shorter in Group D than in the other three groups. Memory retention of the pin-prick examination was reported by four patients in Group A. The present results indicate that 5-10 mL saline is the optimal volume for epidural injection when using midazolam 0.05 mg kg-1 for post-operative analgesia following upper abdominal surgery.