07 - Local Anesthetics

Question 1

Local anesthetics work by causing the loss of

Answer 1

sensory
motor
autonomic function

Question 2

The resting potential of a cell membrane is due to _______. Voltage gated Na and K channels depolarize the membrane, leading to

Answer 2

Na-K-ATPase

action potentials

Question 3

LA enter the cell and bind to

Answer 3

Voltage-gated Na channels to prevent Na influx and slows conduction
May bind to other channels as well (K, Ca, NMDA)

Question 4

How many types of nerve fibers are there? List them in order from smallest to largest.

Answer 4

3

C < B < A

Question 5

What is a differential block?

Answer 5

= Autonomic (C and B) -> Sensory (C and A) -> Motor (A)

Question 6

Nerve fibers are surrounded by ____ and bundled into ______ which are surrounded by

Answer 6

endoneurium
fascicles
perineurium

Question 7

Groups of fascicles surrounded by epineureum?

Answer 7

Axons

Question 8

Nerves can be surrounded by a

Answer 8

myelin sheath

Question 9

LAs don’t fight their way through the myelin, they bind at ____ between the myelinated segments

Answer 9

Nodes

Question 10

Myelinated fibers (B) are ____ to LA than nonmyelinated fibers (A, C)

Answer 10

more sensitive

Question 11

The generalized notion that LA block the smallest fibers first or most is

Answer 11

CLEARLY WRONG

According to Miller

Question 12

Small fibers (C) are ____ to LA than large fibers (A)

Answer 12

more susceptible

Question 13

What is the sequence of a differential block?

Answer 13

B -> C -> A

Question 14

What is the sequence of loss for sensory fibers?

Answer 14

Temp -> pain -> touch -> deep pressure -> proprioception

Question 15

Local anesthetics are ____. How do they become charged?

Answer 15

Weak bases

Accepting a proton on the amine

Question 16

The protonated species of a LA is

Answer 16

More potent

Question 17

pKa of amides

Answer 17

7.6-8.1

Question 18

pKa of esters

Answer 18

8.2-9.0

Question 19

The ability of an LA to penetrate membranes depends on its

Answer 19

lipid solubility, charge, size

Question 20

Adding HCO3 with an LA ____ onset, but can cause

Answer 20

speeds

precipitation (bupivicaine)

Question 21

The density of a block depends on

Answer 21

concentration - need enough drug to saturate binding sites and prevent transmission of AP
volume - need to block a critical length of nerve fiber

Question 22

The duration of action of a block correlates with

Answer 22

lipid solubility

Question 23

LAs are rapidly absorbed through _____ but poorly through

Answer 23

Mucous membranes (conjunctiva, trachea, oropharynx)
Intact skin

Question 24

What is EMLA cream?

Answer 24

Stands for Eutectic Mixture of Local Anesthetics - eutectic mixture of equal quantities by weight of lidocaine and prilocaine.

Question 25

What is the onset of EMLA cream and its depth of penetration?

Answer 25

1 hour | 3-5 mm

Question 26

EMLA cream can cause?

Answer 26

Methemoglobinemia

Question 27

Systemic absorption of LA is proportional to ______ and

Answer 27

Vascularity, vasoconstriction IV > tracheal > intercostal > caudal/epidural > peripheral nerves > subcutaneous

Question 28

Avoid epi on

Answer 28

fingers, toes, penis, nose

Question 29

The only local anesthetic that causes vasoconstriction is

Answer 29

COCAINE!!!

Question 30

Vasoconstriction with LA causes increased ____ and decreased _____. This is less pronounced with

Answer 30

Neuronal uptake Redistribution Bupivicaine

Question 31

Which LA are esters and which are amides?

Answer 31

Esters have one i and amides have two i

Question 32

How are esters metabolized?

Answer 32

Ester hydrolysis by pseudocholinesterase | Excreted in urine

Question 33

There is no pseudocholinesterase in

Answer 33

CSF

Question 34

Procaine/benzocaine can cause formation of PABA (4-aminobenzoic acid) which can cause

Answer 34

allergic reaction

Question 35

Which ester is partially metabolized in the liver?

Answer 35

COCAINE

Question 36

Amides are metabolized in the

Answer 36

liver

Question 37

T or F. Metabolization of esters is faster than amides.

Answer 37

True, ester hydrolysis is rapid

Question 38

Toxicity of LA is treated by

Answer 38

Benzos (caution with thiopental, propofol)

Question 39

Toxicity spectrum of LA

Answer 39

Circumoral/tongue numbess, dizziness, tinnitus, blurred vision Restlessness, agitation, nervousness, slurred speech, drowsiness, LOC Muscle twitching, seizures

Question 40

Lidocaince can ____ CBF and minimize increase of ____ with intubation

Answer 40

decrease | ICP

Question 41

A lidocaine infusion can decrease MAC by

Answer 41

40%

Question 42

What are the effects of COCAINE?

Answer 42

euphoria, restlessness, tremors, convulsions, respiratory failure

Question 43

Repeated doses of lidocaine and tetracaine can cause

Answer 43

Cauda equina syndrome

Question 44

What can be used to treat ventricular arrhythmias?

Answer 44

IV lidocaine

Question 45

LA can sometimes cause cardiac arrest. The cardiotoxicity is reversed by

Answer 45

Intralipid

Question 46

This LA rapidly blocks Na channels and can be difficult to resuscitate

Answer 46

IV bupivicaine

Question 47

Are esters or amides more likely to cause allergic reaction? Why?

Answer 47

Esters They are derived from PABA PABA = procaine and benzocaine allergy

Question 48

How does cocaine work?

Answer 48

Prevent NE reuptake

Question 49

Methemoglobinemia is commonly caused by ______. What do you use to treat it?

Answer 49

Prilocaine and benzocaine, sometimes lidocaine Methylene blue Met Hgb >10% Met Hgb > 50% is severe