L21 local anesthetics

Question 1

General mechanism of local anesthetics

Answer 1

Bind to sodium channels in the nerves to block nerve transmission

Question 2

differences between myelinated and non-myelinated nerves

Answer 2

myelinated you only need to block about 3 nodes of ranier while unmyelinated the length that must be blocked is longer - they are more difficult to block

Question 3

Core vs. Mantle fibers block

Answer 3

core is on the inside of a peripheral nerve and mantle fibers surround. Nerves going to peripheral never are more towards the core therefore the anesthetic needs to penetrate deeper to reach them. onset begins proximal and moves distal

Question 4

Fiber class A

Answer 4

myelinated fibers - larger fibers making them more difficult to block (A alpha is the biggest)

Question 5

Fiber class B

Answer 5

myelinated fibers- very small - the easiest to block

pre-ganglionic sympathetic

blocked with all anesthetics (sympathetic blockade)

Question 6

Fiber class C

Answer 6

unmyelinated fibers- more difficult to block

visceral pain - generalized dull slow pain

Question 7

A alpha fibers do

Answer 7

largest and hardest to block are responsible for motor

Question 8

A beta fibers

Answer 8

tactile, proprioception, touch

Question 9

A delta

Answer 9

pain, cold, temperature, smallest easiest of A group

fast, instant pain

Question 10

order of blockage difficulty

Answer 10

sympathetics>pain>motor

Question 11

3 states of sodium channels

Answer 11

1. resting - M-gate closed, H-gate open
2. Open - M-gate and H-gate open
3. Inactivated- M-gate open, H-gate closed

Question 12

where do local anesthesics bind

Answer 12

on the sodium channels on the inside of the cell- must be lipophilic.

Question 13

frequency dependent blockade

Answer 13

in active nerves (fire more often) will be more quickly blocked by local anesthetic

bind more easily to open or inactivated Na+ channels

Question 14

2 groups of local anethetics

Answer 14

esters

amides

Question 15

molecular structure of local anesthetics

Answer 15

all have benzene rings and tertiary amine groups allowing for a lone electron pair that can accept or donate electrons (give a charged and uncharged forms)

most are weak bases (except benzocaine)

% charged depends on pH and pKa

charged molecule bind to the sodium channel better but only the uncharged can cross the lipid bilayer

Question 16

why add sodium bicarbonate

Answer 16

faster onset time for local anesthetics because increasing the pH around the anesthetic molecules increases the number in the uncharged form which is easier to cross membranes into cells

Question 17

onset time primary determinants

Answer 17

pH and pKa

higher pH and lower pKa speeds up the onset time bc you get more molecules in the uncharged form

Question 18

primary determinant of potency

Answer 18

lipid solubility - more soluble = more potent (need less)

Question 19

protein binding affects

Answer 19

duration (theses are not blood proteins) More binding=longer lasting

anesthetics bind proteins on the nearby tissues creating a sink that can be slowly released to the nerve

Question 20

why would you add epinephrine to a local anesthetic

Answer 20

for vasoconstriction - reduces blood flow - keeps the anesthetic closer to the nerve

more important for drugs that are not very highly protein bound

also helps confirm that the drug is not being injected into the blood stream (if in blood vessel it will increase HR)

Question 21

neuraxial anesthesis

Answer 21

sinal and epidural- indications for a surgery chest or below\
do your injection around L4/L5

Question 22

where does the spinal cord end

Answer 22

adult - L1

infant- L3

Question 23

spinal vs epidural

Answer 23

spina- inject around the caudal equina (L3-L4) the anesthetic will diffuse up and everything below that point will be blocked

epidural - block at nerve roots, can be done at any level, outside the dural and CSF. some will spread up and down and the nerves around the site will be blocked but there is sparing of the nerves below

Question 24

respiratory affects with LAs

Answer 24

block of sympathetics lowers BP (arterial and venal dilation) and if it decreases too low than you could have decreased blood to the brain which could lead to a respiratory arrest

Question 25

CV affects with a local anesthetic

Answer 25

sympathectomy- arterial dilation and venodilation reduces BP

bradycardia- unopposed vagal stimulation of heart

Question 26

order of absorption

Answer 26

intercostal>caudal>epidural

must be very careful with intercostal bc there is the greatest change of overdose

highly protein bound or lipophilic can become sequestered decreasing absorption

pt caracteristics

Question 27

high blood flow affect on local anesthetics

Answer 27

higher blood flow = more absorption

Question 28

Elimination of esters

Answer 28

metabolized in the plasma by plasma cholinesterase (same as succ)

Question 29

amides elimination

Answer 29

metabolized in the liver

Question 30

max recommended dose of bupivacaine

Answer 30

3mg/kg in adults and 2.5 mg/kg in infants

Question 31

max recommended dose of lidocaine

Answer 31

5 mg/kg plain
7 mg/kg with epi

bc epinephrine vasoconstricts to increase absorption of drugs that are not highly protein bound

Question 32

neurotoxicity

Answer 32

excitatory lightheadedness, numbness can lead to seizures worsened by acidosis (less protein binding and more blood flow to brain)

Question 33

Cardiovascular toxicity

Answer 33

usually happens after neurotoxicy (4X-2X the concentration) (or too large of a load given so both happen at the same time)

the heart has the same voltage gated sodium channels as the nerves

direct vasodilation
inhibition of normal sympathetic nervous symptom responses
cocaine- arrhythmias

heart block, slurred QRS,

Question 34

ways to prevent CV toxicity

Answer 34

aspirate on needle before injection to make sure not in a blood vesicle

inject with epi

Question 35

if CV toxicity occurs

Answer 35

ABCs
no lidocaine
stop seizures

specific antidote– intralipid (very lipophilic can absorb anesthetics out of the blood stream)

Question 36

posterior puncture headaches

Answer 36

common complication
worse standing than laying
do a blood patch

Question 37

esters

Answer 37

Cocaine HCl
Procaine HCl
Tetracaine HCl
Benzocaine (only one that is not a weak base)

Question 38

Amides

Answer 38

Lidocaine HCl (only one that can be given IV)
Mepivacaine HCl
Bupivacaine HCl
Ropivacaine