Local Anaesthetics Flashcards
LA (a) blocks (b) when applied to a (c) area of the body
HINT:
(a) reversibly/irreversibly?
(b)
(c) large/restricted?
(a) reversibly
(b) nerve conduction
(c) restricted
LA reversibly blocks nerve conduction when applied to a restricted area of the body
Which type of neurone detects pain?
nociceptors - sensory neurone
Which chemical structures from LA?
- aromatic ring
- amine group
- linkage
What property does the aromatic ring provide?
makes LA lipid soluble
Which structural group can be ionised if it picks up H+?
amine group
What is the significance of the linkage group?
site of metabolism:
enzymes breaks down LA at the linkage group
What type of chemical group is the linkage?
Can be esters or amides
Will a LA with an ester linkage group break down faster or slower than a LA with an amide linkage group?
quicker
Which of the following have an ester linkage?
procaine, lidocaine (lignocaine), prilocaine, bupivacaine
procaine
lidocaine, prilocaine + bupivacaine have an amide linkage
Which of the following have a long duration?
procaine, lidocaine (lignocaine), prilocaine, bupivacaine
bupivacaine
Which of the following have a medium duration?
procaine, lidocaine (lignocaine), prilocaine, bupivacaine
lidocaine
prilocaine
Which of the following have a short duration?
procaine, lidocaine (lignocaine), prilocaine, bupivacaine
procaine
LA are (weak)/(strong) (acids)/(bases)
What determines its ionisation state?
weak bases
pH determines ionisation state
If the environment is alkaline, will there be more unionised/ionised LA molecules
more unionised
Which is the more common state of LA molecules at a physiological pH?
unionised + ionised bother present
BUT ionised > unionised
Which LA molecules are lipid soluble?
ie, ionised/unionised
unionised molecules are lipid soluble
How does LA stop detection of pain?
- anaesthetic present outside the neurone
- unionised LA molecules pass across neurone membrane + enter axon
- unionised LA molecules inside the neurone become ionised
- ionised LA molecules block open Na+ voltage gated channels
- = AP can’t be generated/propagated + signal isn’t transmitted
LA gives rise to use dependant block. What does this mean?
ionised LA molecules block open Na+ channels
channels only open if stimulus is present to generate AP
—> more painful stimulus = more open channels
= blocked by ionised LA
DEGREE OF BLOCK PROPORTIONAL TO RATE OF STIMULATION
Why does acidity reduce effectiveness of LA?
eg, during inflammation/infection
increased acidity = more LA molecules ionised
= few unionised molecules enter the axon
= fewer molecules available to block to Na+ channels
If a patient does have an infection, should the procedure be done?
better to give antibiotics to remove the infection/inflammation and increase effectiveness of LA
Which nerves are more sensitive to LA? Wider/narrower?
narrower
C type neurones + A delta neurones = nociceptors
motor neurones = wider neurones
Are C type neurones myelinated?
no
Where is topic anaesthesia administered? How effective is it?
Applied to the skin
Not very effective
- skin has multiple layers = hard for LA to diffuse across
Where is infiltration anaesthesia administered?
When is it administered?
injected into skin
eg, when getting stitches/tooth extraction
