EXAM #3: LOCAL ANESTHESIA Flashcards
What are the types of local anesthesia?
1) Topical
2) Perineural Infiltration
3) Nerve Block
4) Spinal Block
5) Epidural block
What is the difference between a spinal block and an epidural block?
Spinal= injection into subarachnoid space
- More reliable
- Irreversible
Epidural= injection into the extradural space
- Less reliable
- More reversible
Outline the path of a pain signal to the brain.
1) Nociceptor
2) Sensory afferent
3) Dorsal horn
4) Spinothalamic tract
5) Somatosensory cortex
What is the result of blocking Na+ channels on primary sensory afferents?
Inhibition of firing i.e. less pain signals going to the brain
What is the difference between protonated and non-protonated LAs?
- Non-protonated (LA) are more lipophilic
- Protonated (LAH+) binds to the Na+ receptor and inhibits it
What are the three sites of action on a Na+ channel?
1) Extracellular side of receptor
2) Intracellular side of receptor*
3) Embed in the lipid bilayer and disrupt the geometry of receptor–impedes function*
Most drugs do a combination of these two*
What are the two broad categories of local anesthetics?
Amides
Esters
What two portions of amides and esters are conserved?
Aromatic ring
Tertiary amine
What is the difference between amides and esters?
Intermediate chain of the chemical structure
What is the mnemonic for telling the difference between amides and esters?
Amides= 2x "i" Esters= 1x "i"
Generally, is the important clinical difference between the amides and esters?
Amides= longer half-life/ duration of action
Esters= short half-life/ duration of action
Why is there a difference in metabolism between amides and esters?
- Amides are metabolized in the liver
- Vs. esters that are metabolized in the blood
What enzyme metabolizes esters?
Butyrylcholinestersase
What is Cm?
Minimum anesthetic concentration: minimum concentration for a standard block
What is the relationship between fiber size and Cm?
Bigger fiber= bigger Cm