Do some operations still need more diamorphine?

The systematic review and meta-analysis by Grape et al. [1] suggests that there is no evidence of benefit to doses of intrathecal diamorphine exceeding 0.2 mg. Their systematic review identified 12 trials (712 patients), 11 of which included only patients undergoing orthopaedic or obstetric procedures. There was a single trial including 30 patients having inguinal hernia repair, lower limb arterial or transurethral surgery [2].

A review of 20 major general surgical procedures in our department from the last 2 months (bowel resections, open, and laparoscopic and robot assisted laparoscopic cystectomies) where we use intrathecal diamorphine for analgesia rather than as a sole technique, found a median (IQR [range]) intrathecal diamorphine dose of 0.73 mg (0.50–0.85 [0.40–1.00]). Such dosing has been typical for years and has produced good results. Recognising the significant evidential shortcomings of a small 20 patient retrospective cohort, 17 out of 20 had nil or mild pain, and moderate pain was only found in those with below average dosing. In total, 90% of patients did not experience nausea or vomiting in the post-anaesthesia care unit, none needed naloxone and there were no unplanned ICU admissions or need for chlorphenamine for pruritus.

The included article by Abuzaid et al. detailed general surgical and vascular operations and was published in 1993 [2]. We are concerned it may not represent the current patient cohort for whom single-shot spinal analgesia is administered specifically to cover long and complex abdominal surgeries. There have been substantial developments in surgical practice since 1993; the growth of laparoscopic and robotic surgery, along with enhanced recovery pathways has meant that operations that might historically have used a thoracic epidural, are now having intrathecal opioid administration. Epidurals are known to have a failure rate of around 30% and can cause hypotension and leg weakness [3]. Anecdotally, there is a fear that they will reduce patient mobilisation postoperatively and prolong hospital stay. Single-shot spinals are a middle ground, providing good analgesia in the immediate postoperative period but allowing patients to mobilise with full leg strength the next day, unencumbered by syringe pumps.

Considering this systematic review, we acknowledge that further dose-finding trials could be conducted. However, it is unlikely that we will convince our colleagues to reduce their dose of intrathecal diamorphine for major abdominal procedures.