GasGasGas - The FRCA Primary Exam Podcast GasGasGas - Neuraxial Opiates for the FRCA Primary
Jun 2, 2025
Dive into the world of neuraxial opiate pharmacology as James unpacks the fascinating journey of opioid molecules in the epidural space. Discover why these opioids are administered, how they differ from systemic options, and the anatomical nuances that affect their behavior. Learn about the comparison between morphine, fentanyl, and diamorphine regarding onset and side effects. Gain insights into managing common issues like nausea and pruritus, and see why understanding their kinetics is vital for optimal clinical decision-making.
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Why Neuraxial Opioids Work
- Neuraxial opioids concentrate drug at spinal dorsal horn receptors for effective analgesia.
- This can reduce systemic side effects but does not eliminate risks like respiratory depression.
Epidural Space Anatomy Shapes Drug Fate
- The epidural is a fat-rich cylinder bounded by bone, ligament and meninges with veins that lack valves.
- Fat, Batson's venous plexus and segmental arteries shape drug distribution and systemic uptake.
The Journey To The Dorsal Horn
- A neuraxial opioid must diffuse across fat, veins, dura, arachnoid and CSF to reach dorsal horn neurons.
- Physicochemical properties determine how well it completes that journey.