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Epidural Opioid Side Effects — FRCA Final MCQ

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ModeratePain MedicineEpidural Opioid Side EffectsFRCA Final

A 48-year-old woman (ASA II, 65 kg) undergoes an open cholecystectomy. Post-operatively she has a thoracic epidural infusion providing excellent pain relief at rest (1/10) but she has nausea scored 7/10 and moderate pruritus. The epidural contains 0.125% bupivacaine with fentanyl 4 mcg/mL at 8 mL/hr. What is the most likely cause of the nausea and pruritus?

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Correct answer: C — Surgical complication – bowel obstruction

Both nausea and pruritus are common side effects of epidural opioids (fentanyl, diamorphine, morphine). Fentanyl at 4 mcg/mL × 8 mL/hr = 32 mcg/hr epidural fentanyl, which provides excellent analgesia but causes opioid-mediated nausea (via chemoreceptor trigger zone stimulation and central opioid effects) and pruritus (via central mu-receptor activation, not histamine). Management: reduce the fentanyl concentration to 2 mcg/mL, add ondansetron 4 mg IV for nausea, and consider low-dose naloxone infusion for pruritus. If symptoms are severe, the epidural can be changed to local anaesthetic only (without opioid).

Reference: RCOA – 2023 – Acute pain management; Faculty of Pain Medicine – 2022 – Epidural analgesia guidelines