Accidental Administration of Mega-Dose-Morphine Intrathecally.

Abstract

Dear Editor, Intrathecal opioid administration is a common practice in major abdominal surgery, to facilitate postoperative pain management and lower total opioid consumption (1). We report a case of accidental administration of mega-dose-morphine intrathecally. A 64-year-old patient of 84 kg weight and 172 cm height presented to the OR to undergo an elective sigmoidectomy due to malignancy. His medical record was significant for Paget’s disease under no medication. For his postoperative analgesia, an intrathecal administration of ropivacaine 15 mg and morphine 100 mcg in total volume of 3 ml was planned, using an atraumatic needle of 25 G. Immediately after, anesthesia induction was facilitated with propofol 2 mg/kg, fentanyl 250 mcg and rocuronium 0.6 mg/kg. Anesthesia was maintained with sevoflurane. The procedure lasted for two hours and was uneventful. Toward the end, medication syringes were checked prior to discard, to discover that, instead of 100 mcg, 1 mg of morphine had been administered due to wrong dilution. The standard practice is to dilute 1 ampule (10 mg) in 10 ml syringe and then aspirate 1 ml and perform a second dilution in another 10 ml syringe. In this case, the second dilution was omitted. The patient was easily recovered from anesthesia and transferred to PostAnesthesia Care Unit (PACU), where he was started on naloxone drip 0.5 mcg/kg/h, under monitoring and continuous O2 administration via nasal canula. 8 h later, he was transferred to general ward under close monitoring for 24 h. The analgesic result was excellent, with the patient reporting pain on Numerical Rate Scale (NRS) equal to 0 for the first 24 h, with the naloxone drip withdrawn afterwards. Notably, the patient did not experience any of the commonest opioid related adverse events, i.e., respiratory depression, somnolence and nausea (2). Similar intrathecal morphine doses have been described in the literature, followed by naloxone infusion, to override the adverse events of morphine. Rebel et al. have reported 10-fold higher doses of naloxone than the one used in our case, with sustained analgesic results (3). The combination of opioid agonist-antagonist has been used even per os, to alleviate the nausea and constipation in managing both acute and chronic pain (4). To conclude, incorrect dosage administration, attributed to human factor, is common. A thorough checking of the dugs must always precede their administration and local protocols to manage such an unfortunate event should be established.