GasGasGas - Anaesthetic Science for Anaesthesia! Local Anaesthetics Quiz: FRCA Primary Viva Practice Questions
Aug 22, 2025
Dive into the intriguing world of local anaesthetics in a quiz format! Explore how sodium channel blockade works and learn about the susceptibility of different nerve fibers. Discover the chemical structures of amide versus ester agents and their unique metabolic pathways. Compare lidocaine and bupivacaine, along with the advantages of levobupivacaine. Find out how infection affects anaesthetic effectiveness and why bicarbonate can speed up onset. Plus, get tips on managing systemic toxicity. It's both educational and entertaining!
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How Local Anaesthetics Work
- Local anaesthetics act on the internal side of voltage-gated sodium channels after crossing the nerve membrane in their unionised form.
- They then re-ionise inside the nerve and preferentially bind open channels producing a use-dependent block.
Myelination Determines Blockade Order
- Fibre susceptibility depends mainly on myelination rather than size alone, with unmyelinated fibres being most susceptible.
- Heavily myelinated motor fibres take longer to block than sensory or autonomic fibres due to their myelination and conduction speed.
Amphipathic Structure Explains Behavior
- Chemically local anaesthetics are amphipathic molecules with a lipophilic aromatic ring and a hydrophilic amine linked by an ester or amide.
- This dual nature allows membrane crossing in the unionised form and receptor binding in the ionised form.