Local Anesthetics

Question 1

Describe the progression of blocking achieved with local anesthetics (i.e. what gets blocked first)

Answer 1

1) transmission of autonomic impulses blocked first
2) somatic sensory block
3) somatic motor block

Question 2

Compared to procaine, lidocaine causes a more _____, ______, and _____ _____ conduction blockade

Answer 2

more rapid, intense, and longer-lasting

Question 3

Which portion of the local anesthetic chemical structure confers anesthetic activity

Answer 3

lipophilic group

Question 4

Describe the MOA of local anesthetics

Answer 4

targets Na channels (plugs them) so Na cannot penetrate the cell membrane and cause depolarization

Does NOT change RMP or threshold

Question 5

LAs preferentially bind Na channels in what configuration?

Answer 5

inactivated-closed state

Question 6

Depth of blockade generated by LAs increases with?

Answer 6

AP frequency (frequency-dependent blockade)

more active nerves will be most sensitive

Question 7

Which has a LOWER Cm (minimum concentration)

1) motor nerves
2) sensory nerves

Answer 7

sensory (motor fibers’ Cm is 2x as much)

Question 8

At least ___ needs to be blocked in order to inhibit conduction

Answer 8

1cm of nerve (3 successive nodes of ranvier)

Question 9

Order of conduction blockade concerning sensations lost

Answer 9

pain/temp > touch > joint > deep sensation

Question 10

Concerning the Ester local anesthetics, which:

1) has the fastest onset
2) strongest potency
3) lasts longest (highest degree of protein binding)

Answer 10

1) Chloroprocaine
2) Tetracaine
3) Tetracaine

Question 11

Concerning the Amide LAs, which:

1) 3 have the greatest potency
2) has the fastest onset
3) 3 have the highest degree of protein binding (last longest)

Answer 11

1) Etidocaine, Bupivacaine, Ropivacaine
2) Lidocaine
3) Etidocaine, Bupivacaine, Ropivacaine

Question 12

How does pH affect ionization of LAs?

Answer 12

HIGHER pH (more alkaline) increases the amount of NON-IONIZED drug present–>increases penetration into tissue, thus increasing efficacy

Question 13

This drug is short acting due to it’s strong stimulation of vasodilation

Answer 13

Lidocaine

Question 14

Though Etidocaine and Bupivacaine cause similar levels of vasodilation, why does Etidocaine have less systemic absorption?

Answer 14

it’s more lipid soluble, so it can be sequestered in tissues

Question 15

Which drugs are impacted by lung extraction? (3)

Answer 15

Lidocaine
Bupivacaine
Prilocaine

Question 16

What factor affects placental transfer of drug? Which drug would cross the least? Most?

Answer 16

degree of protein binding

Least transfer–>Bupivacaine (95% bound)

Most–> Prilocaine (55% bound)

Question 17

Why don’t ester LAs undergo placental transfer?

Answer 17

undergo rapid hydrolysis

Question 18

How are ester LAs metabolized? Exception?

Answer 18

hydrolysis via plasma cholinesterases

Exception: Cocaine (hepatic)

Question 19

Metabolite generated with ester LA metabolism? Significance?

Answer 19

Paraaminobenzoic acid–can cause allergic reaction

Question 20

How are amide LAs metabolized?

Answer 20

hepatic metabolism via microsomal enzymes

Question 21

Which LA does NOT induce vasodilation?

Answer 21

Ropivacaine

Question 22

Which site of injection poses the greatest risk of systemic toxicity and why?

Answer 22

Intercostal injection–high degree of vascularity

Question 23

Signs of toxicity occur in what system first?

Answer 23

CNS

Question 24

Which drug has the greatest potential for causing cardiotoxicity? Least potential?

Answer 24

Bupivacaine

Lidocaine (least risk)

Question 25

For which clinical use of LAs is tetracaine contraindicated?

Answer 25

peripheral nerve block anesthesia

slow onset, high risk of toxicity