Intrathecal Analgesia

Intrathecal Opioid

  • Lowest effective dose (usually 100-150µg; less than 300µg) should be used
  • Respiratory monitoring should occur for at least 18-24 hours following a single dose
  • Intrathecal morphine and fentanyl prolong spinal anaesthetic block
  • Morphine is the most commonly studied drug
    Typically 100-500µg used
    • Generally higher doses used in cardiac or thoracic surgery
    • No benefit seen in exceeding 300µg
    • No strong-dose response relationship demonstrated in meta-analyses
  • Quality of analgesia:
    • Similar to epidural for liver resection
    • Duration of ~18-24 hours
      • Reduction in morphine use may extend up to 48 hours
    • Prolongs duration of intrathecal anaesthesia
    • High degree of patient satisfaction, despite side effects
  • Complications include:
    • Nausea/Vomiting
    • Pruritus
      10-15%.
      • Amenable to subcutaneous naloxone
    • Urinary retention
    • Respiratory depression
      • May be:
        • Hypoxic or hypercapnoeic with an normal respiratory rate
        • ↓ respiratory rate with normal gases
        • Pupil size does not correlate with degree of respiratory depression
      • Typically biphasic
        Second peak is delayed, occurring at 8-12 hours.
      • NNH 15-84
        More common compared to PCA.

Intrathecal Adjuncts

  • Intrathecal clonidine improves duration of analgesia and anaesthesia
  • Intrathecal adrenaline improves duration of analgesia and anaesthesia when used with local anaesthetics

References

  1. Schug SA, Palmer GM, Scott DA, Alcock M, Halliwell R, Mott JF; APM:SE Working Group of the Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine (2020), Acute Pain Management: Scientific Evidence (5th edition), ANZCA & FPM, Melbourne.