Local Anesthetics

Question 1

local anesthetics

Answer 1

reversibly block the propagation of electrical impulses along nerves

Question 2

effect of local anesthetics on nerve conduction physiology

Answer 2

prevent stimuli from reaching the threshold, NOT lowering the resting state

Question 3

Main MOA of local anesthetics?

Answer 3

block voltage-gated sodium channels

Question 4

Order of the Differential Blockade

Answer 4

1. Vasodilation
2. Loss of sensation of temperature
3. Loss of sharp pain
4. Loss of feeling of light touch
5. Loss of motor activity

Question 5

Why does the differential blockade occur the way that it does?

Answer 5

dependent on type of nerve fiber - less or non-myelinated axons will be the first susceptible to anesthetic

Question 6

Critical Length

Answer 6

anesthetic must block 3 OR MORE NODES OF RANVIER to stop the impulse from propagating (otherwise it could jump and continue down the nerve)

Question 7

3 Parts of the Chemical Structure of a Local Anesthetic

Answer 7

1. lipophilic benzene ring
2. intermediate chain (ester or amide)
3. hydrophilic amine group

Question 8

What intermediate chain do we see more of - esters or amides?

Answer 8

amides (they are metabolized by the liver)

Question 9

4 Main Properties Influencing Local Anesthetic Activity

Answer 9

1. Molecular Weight
2. pKa (MOST IMPORTANT)
3. Lipid Solubility
4. Degree of protein binding

Question 10

pKa effect on speed of onset

Answer 10

higher pKa = slower onset

Question 11

physiologic pH

Answer 11

7.4

Question 12

pKa of local anesthetic and physiologic pH

Answer 12

the pKa which is closer to physiologic pH will have a faster onset

Question 13

effect of lipid solubility on speed of onset

Answer 13

higher lipid solubility = delayed onset (there’s fat in lots of places in the body so it will go there instead)

Question 14

effect of protein binding on duration of action

Answer 14

higher protein binding will INCREASE the duration of action

Question 15

What drug is pharmacologically active - free or bound?

Answer 15

free

Question 16

Nocita

Answer 16

encapsulated bupivacaine to slow release

Question 17

Do local anesthetics work in inflammation?

Answer 17

no, because the pH is so low (6.0)

Question 18

order of absorption of local anesthetics
brachial plexus - sciatic/femoral - intercostal - epidural

Answer 18

1. Intercostals (HIGHLY VASCULAR)
2. Epidural
3. Brachial Plexus
4. Sciatic/Femoral

Question 19

True or False: Local anesthetics are the only analgesics that stop transduction or transmission of nociception.

Answer 19

TRUE

Question 20

Adverse effects of local anesthetics are mainly caused by?

Answer 20

HUMAN ERROR (inadvertent IV injection or too high of a dose)

Question 21

What two systems will be adversely affected if a local anesthetic is overdosed?

Answer 21

1. CNS (at two times the safe dose)
2. Cardiovascular (at ten times the safe dose, and can be fatal)

Question 22

Best treatment if overdosed?

Answer 22

IV lipid emulsion (aka le bacon) and SUPPORTIVE CARE

Question 23

Lidocaine

Answer 23

most versatile, intermediate acting, MAC sparing

can be given IV

Question 24

Mepivacaine

Answer 24

similar to lidocaine, lasts a little longer, more commonly used in our horses

Question 25

Bupivicaine

Answer 25

slow onset, long acting, highly cardiotoxic; good for differential blockade

Question 26

Short Acting Ester Local Anesthetic?

Answer 26

procaine (won’t really see used clinically)

Question 27

3 Common Uses of Local Anesthetics

Answer 27

1. Peripheral Nerve Blocks (dentistry, ortho, incisional blocks)
2. Epidural (tail amps, C-sections)
3. Topical (IV catheter placement)