Local Anesthetics

Question 1

Esters:

• short duration
• long duration
• surface action

Answer 1

short duration: procaine

long duration: tetracaine

surface action: benzocaine, cocaine

Question 2

Amides:

• medium duration
• long duration

Answer 2

medium duration: lidocaine, mepivacaine

long duration: bupivacaine, ropivacaine

Question 3

Local Anesthesia: definition

Answer 3

sensory transmission from a localized area to the CNS is blocked

Question 4

Local Anesthetics: MOA

Answer 4

• block voltage dependent Na channels of excitable membranes
• reduce influx of Na ions
• prevent depolarization of the membrane
• block conduction of AP

Question 5

Role of nonionized (uncharged) and ionized (charged) forms in the MOA

Answer 5

nonionized: reaching the receptor site (penetrates the tissue)
ionized: cause the effect (active drug)

Question 6

What can be added to the local anesthetics to accelerate the onset of action?

Answer 6

sodium bicarbonate (enhances intracellular access)

Question 7

What can be added to short acting local anesthetics to prolong duration?

Answer 7

alpha agonist sympathomimetic vasoconstrictor (epinephrine)

Question 8

Why do we add epinephrine to shorter acting local anesthetics?

Answer 8

duration of action is limited unless blood flow to the area is reduced (higher sustained local tissue concentrations)

E will prolong the duration

Question 9

Where are esters metabolized?

Answer 9

bloodstream by plasma cholinesterases (very rapid)

Question 10

Where are amides metabolized?

Answer 10

liver (higher risk of toxicity w/ liver dysfunction)

Question 11

Which fibers are blocked most easily?

Answer 11

small (vs large)
myelinated (vs unmyelinated)
peripheral (vs core)
type B (vs type C)

Question 12

What are the effects of central neuraxial techniques and their ADEs?

Answer 12

motor paralysis (impaired respiratory activity)

autonomic nerve blockade (hypotension)

Question 13

What are some cases in which motor paralysis would be disadventageous?

Answer 13

may limit the ability to bear down during delivery (obstetrical labor)

can hamper ability to ambulate w/o assistance –> falls

may interfere w/ bladder function –> urinary retention

Question 14

Orderly evolution of block components

Answer 14

sympathetic transmission –> temperature –> pain –> light touch –> motor block

Question 15

What qualifies successful surgical anesthesia?

Answer 15

ablation of pain AND loss of touch

Question 16

What tissues should we not inject with anesthesia+vasoconstrictor?

Answer 16

fingers
nose 
penis
toes
earlobes

Question 17

Which epidural anesthesia was banned by the FDA in obstetrics and why?
What is the antidote?

Answer 17

bupivacaine
ADE: cardiotoxicity

antidote: lipid resuscitation

Question 18

A alpha nerve fibers

Answer 18

proprioception (muscle sense), motor

Question 19

A beta nerve fibers

Answer 19

touch, pressure

Question 20

A delta nerve fibers

Answer 20

pain, temperature

Question 21

C nerve fibers

Answer 21

pain, temperature, itch

Question 22

Amides: ADEs

Answer 22

CNS:

• excitation
• seizures

CV:

• vasodilation
• hypotension
• arrhythmias (bupivacaine)

Question 23

Cocaine: MOA

Answer 23

blocks Na channels
and
intrinsic sympathomimetic actions

Question 24

Esters: pharmacokinetics

Answer 24

rapid metabolism via plasma esterases – short half lives

Question 25

Esters: ADEs

Answer 25

CNS:

• excitation
• seizures

Question 26

Cocaine: ADEs

Answer 26

when abuse:
HTN
seizures
cardiac arrhythmias

Question 27

What conditions would cause delayed metabolism and decreased elimination of lidocaine?

Answer 27

impaired hepatic blood flow (CHF)

Question 28

Toxicity (CNS and CV)

Answer 28

CNS:
lightheadedness/sedation
restlessness
nystagmus
tonic clonic convulsions 

CV:
vasodilator
heart block
arrhythmias
hypotension

Question 29

Prilocaine: unique effect

Answer 29

metabolized to o toluidine (can convert hemoglobin to methemoglobin)

Question 30

Ester type metabolized products: unique effect

Answer 30

can cause antibody formation

Question 31

Treatment for Toxicity

Answer 31

no antidote

manage convulsions w/ IV diazepam

Question 32

EMLA cream:

• what is it
• MOA
• uses

Answer 32

lidocaine + prilocaine

penetrates keratinized layer of skin –> localized numbness

peds venipuncture, IV catheter placement