24 Local Anesthesia

Question 1

What are the key differences of local anesthetics from general anesthesia?

Answer 1

nerve blockade to eliminate SENSORY and MOTOR response to a surgical stimulus

Question 2

What are the 2 classifications of local anesthetics?

Answer 2

Amide and ester

Question 3

Where are the amides metabolized?

Answer 3

liver

Question 4

Where are the esters metabolized or by what?

Answer 4

plasma esterases

Question 5

Cocaine and benzocaine are used as what in local anesthesia?

Answer 5

topical esters

Question 6

Amides have what in their name to help give you a clue?

Answer 6

an I before the caine

Question 7

T-F–local anesthetics are more potent when they are lipid soluble?

Answer 7

true

Question 8

Is procaine high potency?

Answer 8

No, low

Question 9

Is mepivacaine and lidocaine intermediate potency?

Answer 9

Yes

Question 10

Is tetracaine and bupivicaine low potency?

Answer 10

No, high

Question 11

T-F–local anesthetics are protonated as a weak acid?

Answer 11

False–protonated but are weak bases

Question 12

Where doe the protonated local anesthetic act?

Answer 12

Binds to the voltage gated Na channel from the intracellular space

Question 13

Na influx is important for what in the nerve?

Answer 13

Initiation of action potential,

Question 14

Small doses of lidocaine can give a good block?

Answer 14

False, need huge doses

Question 15

A lot of locations for lidocaine on a nerve causes what?

Answer 15

scrambles the conduction

Question 16

T-F–Esters pKa are lower that amides?

Answer 16

False

Question 17

As tissue pH decreases the amount of local anesthetic in the nonionized form _________?

Answer 17

decreases

Question 18

T-F–local anesthetics differ in duration of action>

Answer 18

True

Question 19

How well do local anesthetics work in acidotic tissue? Outcome?

Answer 19

not very well

Drug cannot enter intracellular space and this is when toxicity can be a major concern

Question 20

What is the henderson hasselbach equation as it relates to local anesthetics?

Answer 20

pH=pKa+log LA/LA+

[LA+=local anesthetic protonated]

Question 21

What is the fraction of neutral local anesthetic to local anesthetic protonated of a drug at pH6.4 and a pka of 7.4?
What about a pH of 8.4?

Answer 21

LA/LA+ = 1/10

LA/LA+=10

Question 22

T-F–local anesthetic drugs bind the extracellular Na channel portion blocking the depolarization and sensory/motor signals.?

Answer 22

False-intracellular

Question 23

Which subclass [2] of nerve fibers are less sensitive (1/2 sensitive) to local anesthetics? What do they do?

Answer 23

Csymp–>autonomic functions

Csens–>pain, temp, touch

Question 24

Nerve subclasses below have what functions?
Aalpha=?
Abeta?
Agamma?
Asigma?
B?

Answer 24

alpha=motor/proprioception
beta=motor/proprio/touch
gamma=muscle tone
sigma=pain/temp/touch
B=autonomic functions

Question 25

Is B or C symp nerve subclass preganglionic sympathetics?

Answer 25

B is. C is postganglionic sympathetics

Question 26

With increasing plasma concentrations, what are the signs and symptoms of local anesthetic toxicity? [There are several, try climbing the latter]

Answer 26

``` Numb Tongue Lighthead vis/aud disturb Unconsciousness Convulsions Coma Respiratory Arrest Cardiac Toxicity ```

Question 27

Does cardiac toxicity come before or after coma in regards to local anesthetic toxicity?

Answer 27

After

Question 28

What type of administration technique of local anesthetic creates the highest plasma concentration levels and subsequently leads to greatest risk of toxicity?

Answer 28

Intercostal | [Then epidural and then subcutaneous]

Question 29

What is used in conduction with local anesthetics to lower the systemic plasma concentration of the drug?

Answer 29

Epinephrine because of its vasoconstrictive actions

Question 30

For local anesthetic toxicity what drugs do we give? [2]

Answer 30

Intralipid-intravenously | Also, barbiturates or benzodiazepines for seizures

Question 31

Are esters or amides local anesthetics more likely to give an allergic reaction to ? [what are the major or more common culprits though?]

Answer 31

Esters [Others are the EPI/preservatives and other drugs used]

Question 32

Ester local anesthetics such as benzocaine for baby teeth have shown what dangerous side effect in children?

Answer 32

methemoglobinemia

Question 33

What local anesthetic is most used for starting IV and minor surgeries?

Answer 33

1% lidocaine intra or subQ

Question 34

What is the Bier Block?

Answer 34

Intravenous injection of anesthetic into extremity that has a tourniquet more proximal to injection [surgeries up to 2 hours, may be useful for chronic pain]

Question 35

How do we find the nerve for a femoral nerve blockade?

Answer 35

electrical stimulator

Question 36

What are the 2 major peripheral nerve blockade for leg surgery?

Answer 36

Femoral and sciatic

Question 37

What is the major toxicity/side effect we must always be concerned about with cocaine?

Answer 37

vasoconstrict--->MI

Question 38

Is ropivacaine the s-isomer or r-isomer of a racemic mixture?

Answer 38

S

Question 39

What is a common additive to increase basicity or create heaviness?

Answer 39

8.5% Dextrose

Question 40

If epinephrine has a 1 to 200,000 ratio, what does this mean?

Answer 40

1 gram to 200,000ml

Question 41

If I wanted to convert an epinephrine 1:200,000 to mcg/ml what would it be?

Answer 41

5mcg/ml [1g/200,000ml--->1,000,000mcg/200,000ml--->5mcg/ml]

Question 42

1% solution of lidocaine contains what g/ml? mg/ml?

Answer 42

1g/100ml 10mg/ml