Local Anesthetics

Question 1

Does a person lose memory with local anesthesia

Answer 1

No - pt remains conscious - drug doesn’t make it to the brain - so no memory loss

Question 2

What is a local anesthetic (LA)

Answer 2

drug that when applied locally can inhibit perception of sensation and prevent movement

Question 3

primary mechanism of action for LA

Answer 3

blocking sodium channels (can bind to other receptors)

can block Na+ channels on any type of fiber - including in heart

Question 4

Nerve bundle

Answer 4

sensory nerves don’t travel on their own but as a bundle

Question 5

What does blocking peripheral sodium channels do

Answer 5

prevents propagation of AP -> prevents release of glutamate and substance p -> prevents ascending pathway = no pain

Question 6

What is a nerve block

Answer 6

inject LA near location of nerve where you want to block sensation. Inject in periphery -> if you inject too near/in spinal cord, it can bind to sensory fibers in spinal cord - will be epidural/spinal block then.

Question 7

Uses/administration of LA

Answer 7

oral nerve block
peripheral nerve block
epidural block
spinal (intrathecal) block

Question 8

Oral nerve block

Answer 8

inject into nerve bundle rather than individual nerve to get stronger block -> will numb entire area where bundle runs

Question 9

Peripheral nerve block

Answer 9

block nerve bundle in periphery

Question 10

Epidural

Answer 10

route of administration
drug released outside of dura mater
drug has to cross dura mater, enter CSF, and come into contact with nerve cord fibers
Most common method -> NOT puncturing dura mater so less chance of infection

Question 11

Spinal (intrathecal)

Answer 11

puncture dura mater, drug directly into CSF
slightly more potent than epidural
Can be used to treat central pain at cell body in spinal cord (intrathecal catheter/pump)

Question 12

What drugs can you give via intrathecal

Answer 12

opioids, alpha-2 agonists, etc

Question 13

LA bind to sodium channels that are

Answer 13

open or inactive (refractory)

Question 14

Degree of inhibition of sodium channels is dependent upon

Answer 14

frequency of action potentials - infrequent AP won’t be inhibited as much as frequent AP

Question 15

Why do you want LA to bind to open or refractory confirmation

Answer 15

b/c once channel is closed, it will reopen and fire an AP. If you can block channel when it’s open or refractory, it prevents closing and thus prevents AP

Question 16

Tonic inhibition

Answer 16

occurs in low frequency firing of AP -> long time btwn AP so LA will dissociate and not block the AP -> limited nerve fiber inhibition

Question 17

example of tonic nerve fiber

Answer 17

nerve bundles in mouth -> this is why oral LA take a while to work

Question 18

Phasic inhibition

Answer 18

occurs in high frequency AP. LA constantly bound to sodium channel b/c it does not have a chance to dissociate before another AP is fired.

Question 19

Does phasic firing of AP indicate pain

Answer 19

Yes -> very active nerve fiber, this is why epidurals in active labor work so well.

Question 20

What can lead to increase in frequency of AP firing

Answer 20

tissue injury or trauma -> LA will block nociceptive fibers or CNS axons better, leading to greater pain inhibition compared to tonic state

Question 21

Do you want a strong, moderate, or weakly hydrophobic LA

Answer 21

moderate is best (wide range of moderate)

Question 22

Why are poorly hydrophobic drugs not effective

Answer 22

cannot cross cell membrane and enter intracellular space, which is where binding site/ sodium channel is

Question 23

why are strongly hydrophobic drugs not effective

Answer 23

will get trapped in lipid bilayer and not cross into intracellular space

Question 24

Moderately hydrophobic LA

Answer 24

procain
tetracain
cocaine
lidocaine
prilocaine
bupivacaine

Question 25

Procaine

Answer 25

Novocain
short acting, low hydrophobicity -> thus rapidly removed and not sequestered in tissue for long
common in dental procedures

Question 26

Tetracaine

Answer 26

long-acting, highly potent
highly hydrophobic
able to remain in tissue near injection for extended period of time
hydrophobicity responsible for high potency
used for epidural and spinal anesthesia.
also used topically

Question 27

Cocaine

Answer 27

medium acting, medium potency
low hydrophobicity
can block catecholamine transporters and act as vasoconstrictor at local site
rarely used in certain eye procedures

Question 28

Lidocaine and Prilocaine

Answer 28

medium duration, moderately potent agen
moderate hydrophobicity
can be used with epinephrine to increase duration of action
MOST commonly used LA
often paired with Epi -> vasoconstricts -> keeps drug at site longer

Question 29

Bupivacaine

Answer 29

highly hydrophobic, long duration of action
epidural, spinal, and peripheral blocks
can be cardiotoxic at high dose
drug can move towards lower end of spinal cord causing “short fusing” effect -> pt has sudden urge to walk around
encourage pt to move around after injection to prevent