Exam 11: Local Anesthetics

Question 1

Which part of local anesthetics’ structure is important for their entry into the axon?

Answer 1

Lipophilic domain

Question 2

Which part of local anesthetics’ structure is important for their action at Na+ channels?

Answer 2

Hydrophilic domain

Question 3

What are the two types of local anesthetics?

Answer 3

Amides (lidocaine)

Esters (procaine)

Question 4

How are Amide local anesthetics metabolized?

Answer 4

Liver (microsomal enzymes)

Question 5

How are Ester local anesthetics metabolized?

Answer 5

Plasma cholinesterase

Question 6

How do the half-lives of Amides compare to Esters?

Answer 6

Amides have longer half-lives because they’re metabolized by liver enzymes as opposed to Esters, which are metabolize by cholinesterase in the plasma

Question 7

Which chemical form of local anesthetics enters the cell?

Answer 7

Unprotonated (LA)

Question 8

Which chemical form of local anesthetics is “active” in inhibiting the Na_ channels?

Answer 8

Protonated (LAH+)

Intracellular pH is lower than extracellular

Question 9

What is the order of neuron sensitivity to nerve block?

Answer 9

Most to least sensitive:
C (pain)
B (autonomics)
A' (pain/temp)
A (motor)
A+ (motor)

Question 10

How can you numb an entire limb?

Answer 10

Intravenous regional anesthesia
Put a tourniquet on and inject LA IV
Only useful up to 2 hours

Question 11

Spinal vs Epidural: Which needs more LA

Answer 11

Epidural

Question 12

Spinal vs Epidural: Which is more intense of a block?

Answer 12

Spinal

Question 13

3 Advantages of Epidural over spinal anesthesia

Answer 13

1. Not limited to below L2
2. No dural puncture = no post-dural puncture headache
3. You can leave a catheter in for long-term pain reduction and fine tune the dosage from there

Question 14

Purpose of giving Epinephrine injection with local anesthetics

Answer 14

Causes vasoconstriction and decreasing absorption

Prolongs duration of effect and reduces the amount of LA needed

Question 15

2 cautions with epinephrine injection

Answer 15

1. Can cause vasodilation at skeletal muscle beds, increasing toxicity
2. Dont use it at peripheral sites (nose, fingers, scrotum, ears)

Question 16

Where can local anesthetics distribute?

Answer 16

Everywhere (cross BBB)
Amides are taken up in fat, brain, kidney, liver, muscle, gut.
Esters are metabolized too fast to be redistributed

Question 17

What does CSF lack?

Answer 17

Cholinesterase

Question 18

Local anesthetic side effects at low doses

Answer 18

Sleepiness, dizziness, restlessness

Lidocaine can cause euphoria

Question 19

Local anesthetic side effects at high doses

Answer 19

Nystagmus, shivering, CNS depression, respiratory failure, convulsions

Question 20

Treatment for local anesthetic toxicity

Answer 20

Benzos and barbiturates

Question 21

Only local anesthetic with intrinsic vasoconstrictive properties

Answer 21

Cocaine

the rest are vasodilators

Question 22

Which local anesthetic is the most cardiotoxic?

Answer 22

Bupivacaine

Question 23

Which 2 local anesthetics can cause methemoglobinemia?

Answer 23

Prilocaine

Benzocaine

Question 24

2 Amide Local Anesthetics

Answer 24

Lidocaine
Bupivacaine
Ropivacaine
Articaine

Question 25

2 Ester Local anesthetics

Answer 25

Benzocaine | Cocaine

Question 26

What is the most widely used Local Anesthetic today?

Answer 26

Lidocaine

Question 27

Lidocaine

Answer 27

Amide Local anesthetic Widely used (including spinals, epidurals, IV) Excellent diffusions and penetration

Question 28

Bupivacaine

Answer 28

Amide Local Anesthetic Long Duration of Action!!! Not recommended for IV injection due to cardiotoxicity

Question 29

Caution with Bupivicaine

Answer 29

Dont inject IV | Cardiotoxic

Question 30

Ropivacaine

Answer 30

New Amide local anesthetic Useful for procedures where you don't want motor block (labor anesthesia) because it's less lipophilic than bupivacaine Reduced CNS/Cardio toxicity Pure enantiomer

Question 31

Articaine

Answer 31

Amide Local Anesthetic | Safer than prilocaine because it metabolized by plasma carboxyesterase (less metabolized in liver)

Question 32

Benzocaine

Answer 32

Ester local anesthetic Used topically (skin/mucus membranes) FDA warning for use in children due to methemoglobinemia

Question 33

Cocaine!!!

Answer 33

Topical use only Only Local anesthetic with inherent vasoconstrictive action No need to co-administer with epi, this could increase toxicity