Epidural diamorphine infusions with and without 0.167% bupivacaine for post-operative analgesia

Forty patients who underwent upper or mid-abdominal surgery were randomly allocated to receive a post-operative epidural infusion of 0.083 mg ml-1 of diamorphine in either 0.167% bupivacaine or 0.9% NaCl solution. The nursing staff, who were unaware of which solution was being infused, managed the patients' pain according to a standardized scheme. They adjusted the epidural infusion rates to 3, 5 or 7 ml h-1 according to the patient's hourly reports of pain on a four point verbal rating scale (none, mild, moderate or severe), aiming to use the lowest allowed infusion rate to prevent or reduce any pain that was more than mild. Additional analgesia was given as diclofenac 75 mg intramuscularly if the patients report moderate pain while on the highest infusion rate. The nurses were instructed to summon anaesthetic help if pain relief was still unsatisfactory after diclofenac, but this was never necessary. Diclofenac was needed by six patients receiving diamorphine in saline and one receiving diamorphine in bupivacaine (P < 0.05). The range of average hourly epidural infusion rates was constrained by design to between 3 and 7 ml h-1 but the median of these values was 5 ml h-1 in the diamorphine-saline group and 3.35 ml h-1 in the diamorphine-bupivacaine group (P < 0.02). In patients receiving diamorphine in saline, a median of 6 (range 0-16) of the 24 h reports were of more than mild pain, whereas in the diamorphine-bupivacaine group, the corresponding figures were 2 (range 0-13) (P < 0.02)).(ABSTRACT TRUNCATED AT 250 WORDS)