Dose response to intrathecal diamorphine for elective caesarean section and compliance with a national audit standard

BackgroundThis double-blind randomised controlled trial investigated the most appropriate dose of intrathecal diamorphine to use with high-dose diclofenac as part of a multimodal analgesic regimen for caesarean section under subarachnoid block. We also wished to establish whether it was possible to satisfy the Royal College of Anaesthetists postoperative pain audit recommendation for this patient group.MethodsOne hundred and twenty patients presenting for elective caesarean section under subarachnoid block were recruited and divided into four groups. Treatment was standard except that patients were given either placebo or one of three different doses of intrathecal diamorphine (100 μg, 200 μg or 300 μg). All patients were given regular paracetamol, high-dose diclofenac and an hourly subcutaneous diamorphine regimen for breakthrough pain.ResultsThere was a dose-dependent improvement in analgesia with intrathecal diamorphine. Only 37.9% of patients given 300 μg of intrathecal diamorphine had a visual analogue pain score of 3/10 or less throughout the study. There was a dose-dependent increase in the incidence of itching with intrathecal diamorphine although the incidence of nausea and vomiting was similar between groups.ConclusionsWe found that for elective caesarean section under subarachnoid block with high dose diclofenac, analgesia was optimal with 300 μg of intrathecal diamorphine. Even the highest dose of intrathecal diamorphine did not achieve the Royal College of Anaesthetists postoperative audit target that 90% of patients should have a pain score of no more than 3/10. We believe that this target is too arduous.