L10: Local Anesthetics (Garcia)

Question 1

chars. of amides

Answer 1

• stable in solution
• enzymatic degradation in the liver
• no p-Aminobenzoic acid metabolite

Question 2

chars. of esters

Answer 2

• unstable in solution
• metabolized in plasma (cholinesterase enzymes)
• p-Aminobenzoic acid metabolite (allergic rxns)

Question 3

amide drugs (DNK)

Answer 3

lidocaine
bupivacaine
mepivacaine
ropivacaine
EMLA

Question 4

ester drugs (DNK)

Answer 4

cocaine
benzocaine
procaine
tetracaine

Question 5

chars. of lidocaine

Answer 5

• must have high plasma conc. before causes toxicity

- short half-life; metabolized quickly

Question 6

bupivacaine chars.

Answer 6

• very lipid soluble; will get highest plasma conc. quickest (easier to get toxicity)
• can cause CNS, CV side effects if given IV

Question 7

which safer: bupivacaine or ropivacaine

Answer 7

ropivacaine (lidocaine safer than ropivacaine)

Question 8

only local anesthetic absorbable into cornified skin

Answer 8

EMLA

-expensive

Question 9

factors that affect onset***

Answer 9

lipophilicity
pKa
conc.
dose and volume
proximity to nerve (closer –> faster onset)
type of nerve (thinner, myelinated nerves easier to block)

Question 10

how does pKa affect onset?***

Answer 10

(pH at which drug will be 50/50 ionized and non-ionized form)
-must be non-ionized to go through membrane, so in an acidic env. of infection/inflamm., even more in ionized form and will have harder time getting into membrane

Question 11

factors that affect duration***

Answer 11

vascular effect: closer to vascular bed will have faster effect
tissue blood flow
vasoconstrictor (will caused prolonged duration)
dose
affinity to Na receptor

Question 12

MOA of local anesthetic***

Answer 12

• Na channel blocker
• acts on neuron axon
• affects depolarization
• decreases n. conduction
• affects both sensory and motor neurons
• may cause vasodilation

Question 13

factors affecting action

Answer 13

pH/pKa (lower the pH, less the drug works)
proximity
dose
volume 
spread (related to volume)

Question 14

CS of neurologic toxicity from local anesthetics

Answer 14

tremor
nervousness
seizures
CC/CNS ratio (higher better; want drugs that have high conc. in serum for CV collapse compared to CNS effect; don’t want cardiotoxic effects to occur until much higher concs.)

Question 15

CS of CV toxicity from L.A.

Answer 15

bradycardia
sinus arrest
fibrillation
bupivacaine

Question 16

infiltration

Answer 16

• injection at the surgical site
• blockage of nociceptive input
• dose

Question 17

Ring Block

Answer 17

Rule of 2-2: 2 blocks on palmar side (dorsal br. of ulnar n. and median n.) and 2 blocks on medial side (radial n. and median n.)
only 3 blocks total!!

Question 18

Bier block

Answer 18

• IV block with lidocaine
• good for toe amputations
• use tourniquet so IV injection doesn’t dilute, and to reduce bleeding (don’t keep on >1hr)

Question 19

epidural

Answer 19

between Co-1 and 2 on horse

-blocks perineal area in standing horse

Question 20

femoral compartmental block

Answer 20

• substitute epidural
• goes into psoas major m. at L4/5
• less invasive than epidural
• only blocks one limb instead of bilateral block
• can be tricky to do right

Question 21

sciatic block

Answer 21

another substitute epidural

Question 22

brachial plexus block

Answer 22

• block of innervations to front limb
• C6-T2 spinal nerves
• C6, radial art, tip of shoulder
• excellent accuracy with U/S