Flashcards in Local anaesthetics Deck (68)
What is general anaesthesia?
Total loss of sensation.
What is local anaesthesia?
Absence of sensation in a specific part of the body.
What are the main methods of local anaesthesia?
-irreversible (ethanol, surgery, etc)
What is a local anaesthetic?
A drug that:
-REVERSIBLY prevents nerve transmission
-to REGION applied
-WITHOUT affecting consciousness
Where along an axon does a local anaesthetic work?
Anywhere along the axon.
-3 neuron chain
What is the mechanism of action of local anaesthetics?
Block voltage-gated Na channels >> no depolarisation/AP.
Where do local anaesthetics bind to Na channels?
Inside cells - has to cross membrane.
What state are local anaesthetics in when they cross the membrane and bind to Na channels?
NON-IONISED when they cross cell membrane
IONISED when they bind to Na channels
What are individual nerve fibres surrounded by?
What are nerve bundles surrounded by?
What is the outermost layer surrounding nerve fascicles called?
What are the layers surrounding nerves? (3)
ENDONEURIUM - surrounds individual nerve fibres
PERINEURIUM - surrounds nerve bundles
EPINEURIUM - outermost, surrounds fascicles
Which part of the nerve are local anaesthetics injected into?
Injected into the area around nerves, not into the nerve.
What layers must local anaesthetics pass through to enter the nerve?
-causes delayed numbness
What are the main types of local anaesthetics?
-LOCAL INFILTRATION (skin incisions)
-NERVE BLOCK (around nerve)
-EPIDURAL BLOCK (around spinal cord)
What are the ideal characteristics of local anaesthetics? (4)
-Good therapeutic index
What is therapeutic index?
-ratio of amount of therapeutic agent that causes therapeutic effect to amount that causes harm
Are local anaesthetics ever injected into nerves for quick action?
Do local anaesthetics produce reversible conduction block?
What was used as the first local anaesthetic?
-Freud noticed numbness around lips
-Koller introduced it
What is the general structure of local anaesthetics? (3)
Aromatic residue + intermediate chain + substituted amino chain.
What are the 2 types of local anaesthetics based on structure?
What are the structural differences between esters and amides?
What is the difference between the naming of ester and amide local anaesthetics?
AMIDES - 'i' before -caine
ESTERS - no 'i' before -caine
Is prilocaine an ester or an amide?
-'i' before -caine
Did Sigmund Freud first used cocaine clinically?
What are the different characteristics between local anaesthetics?
-Onset of action
-Duration of action
What is the effect if pKa (anaesthetic) = pH (body)?
Ionised and non-ionised forms of LAs are equal.
>> quicker onset
What is the effect if pKa > pH?
Ionised form > unionised form.
- delayed onset