Local anesthetics

Question 1

metabolized by tissue and blood butyrylcholinesterase (peudocholinesterase) (short T1/2 <1min)
Examples (4)

Answer 1

Esters

Cocaine
Procaine
Tetracaine
Benzocaine

Question 2

metabolized by liver amidase
( long T1/2 1.5-2h), and liver diseases affect
Examples (5)

Answer 2

Amides (“i” before “caine”)

Lidocaine
Bupivacaine
Mepivacaine
Etidocaine
Prilocaine

Question 3

if pt is allergic to procaine, which one do you use for anesthesia?

Answer 3

Amides

Question 4

MOA of local anesthetics

Answer 4

Inhibit fast-sodium channel and depolarization of nerve

Question 5

Why do ester anesthetics have allergy

Answer 5

they are metabolized to Paraaminobenzoic acid (PABA) derivatives

Question 6

What are the advantage to add a vasoconstrictor to a LA?

Answer 6

1. Decr. systemic absorption due to local vasoconstriction (Higher local concentration of LA)
2. Decr. systemic toxicity (Decr. blood level up to 1/3)
3. Decr. local bleeding (improve visualization of surgical field)
   Caution in end arteries! (ischemic necrosis)

Question 7

Which LA is most cardiac toxic?

Answer 7

Bupivacaine is most cardiotoxic, contraindicated in epidural anesthesia in Obstetrics

Question 8

How do you treat cardiac arrest after LA?

Answer 8

lipid emulsion treats cardiotoxicity

Question 9

All LA are vasodilators or vasoconstrictors?

Exception

Answer 9

All LA are vasodilators (block symp. nerve) – hypotension

except Cocaine – inhibit NE reuptake- vasoconstriction

Question 10

CNS side effects of LA toxicity (after entering circulation)

Answer 10

Circumoral, tongue numbness, metallic taste - earliest sign
Nystagmus, muscle twitching
Seizures
Depression / Loss of Consciousness

Question 11

How do you treat CNS toxicity of LA?

Answer 11

Diazepam/Midazolam/Propofol (for seizures), succinylcholine, O2

Question 12

MOA of cardiotoxicity caused by LA?

Answer 12

blockade of Na+ channels in heart - depresses cardiac conduction – ventricular arrhythmias, A-V blockage, decreased ventricular contraction, asystol, cardiac arrest, CV collapse

Question 13

oxidation of iron in hemoglobulin?

a. What is this lol
b. Caused by which LA?
c. how do you treat?

Answer 13

a. methemoglobinemia
b. Prilocaine and benzocaine
c. Treated with ascorbic acid or methylene blue (reducing agents)

Question 14

Which nerve fiber most sensitive to blockade?

Answer 14

smaller diameter and have high firing rate (so more inactivated sodium channel) - state and use dependent

Also: Fiber position in the nerve trunk
Myelination ( nerve with myelination is blocked more fast)