Lecture 07_Fall

Question 2

Of the three types of nerve fibers (A,B,& C) ___ nerve fibers are the smallest and slowest and __ are the biggest and fastest.

Answer 2

C nerve fibers are the smallest and slowest and A are the biggest and fastest.

Question 3

The action of local anesthetics includes loss of ____, ____, and ___ function

Answer 3

sensory, motor, and autonomic

Question 4

Which nerve fibers are responsible for pain and cold temperature?

Answer 4

A-delta, and C

Question 5

How do LAs work?

Answer 5

They enter the cell and bind to voltage-gated Na channels, prevent the influx of Na, which slows conduction

Question 6

Which fibers are unmyelinated?

Answer 6

only C fibers (Sensory - dull pain, temp, touch)

Question 7

What is the sequence of the differential blockade?

Answer 7

Autonomic -> Sensory -> Motor

B->C->A

Question 8

Nerve fibers are surrounded by ____ and bundled into _____ which are surrounded by _______. ____ are groups of fascicles are surrounded by ______.

Answer 8

endoneurium, fascicles, perineurium, Axons, epineurium

Question 9

LAs bind at the ____ in between myelinated segments

Answer 9

nodes

Question 10

Do LAs have faster onset with myelinated or non-myelinated fibers?

Answer 10

myelinated

Question 11

Do LAs have faster onset with small fibers or large fibers?

Answer 11

small

Question 12

T or F. Recovery from LAs is usually in the opposite order of onset.

Answer 12

True.

Usually you lose B
(Autonomic) -> C (Sensory) -> A (Motor)

And they return in the opposite order:
A (Motor) ->C (Sensory) -> B (Autonomic)

Question 13

List the order you lose your senses in with a local block.

Answer 13

Temp (cold -> hot) -> pain -> touch -> deep pressure -> proprioception

Question 14

_ fibers are mostly motor, _ fibers are mostly autonomic, and ___ fibers are mostly sensory

Answer 14

A, B, C

Question 15

Local anesthetics are weak ____ that become charged by accepting a proton on the _____.

Answer 15

Bases, amine

Question 16

What are the two groups of LAs?

Answer 16

Esters and Amides

Question 17

How does an acidic environment effect the onset of LAs?

Answer 17

Acidic environment -> more charged species -> slower onset

Question 18

Onset of action of LAs depends on ___, ___, and ___.

Answer 18

lipid solubility, charge, and size.

Question 19

Systemic absorption of local anesthetics is proportional to ____ and inversely proportional to ____.

Answer 19

vascularity, vasoconstriction

Question 20

T or F. EMLA cream can cause methemoglobinemia.

Answer 20

true

EMLA cream is lidocaine and prilocaine

Question 21

Although LAs primarily bind to ___ channels, they may bind to ___, ___, and ___ channels as well.

Answer 21

Although LAs primarily bind to Na channels, they may bind to K, Ca, and NMDA channels as well.

Question 22

LAs are made up of a benzene ring, link and amine group. Which part of this structure indicates whether it is an ester or amide?

Answer 22

the link is either an ester or an amide

Question 23

T or F. LAs block the smallest nerve fibers first/most.

Answer 23

False - it depends on myelination. Myelinated fibers may actually be more sensitive to LAs than non-myleinated fibers.

Question 24

T or F. LAs with a pKa closer to physiologic pH will have a faster onset.

Answer 24

True. LAs with a pKa closer to physiologic pH will have a faster onset because the concentration of nonionized form is higher - and that is the form that is lipid soluble

Question 25

The density of a block depends on ___ and ___.

Answer 25

concentration and volume

Question 26

Duration of LA action correlates with ____.

Answer 26

lipid solubulity

Question 27

Place the following areas in order (from greatest to least) for systemic absorption of LAs

peripheral nerves, tracheal, caudal/epidura, IV, subcutaneous, intercostal

Answer 27

IV > tracheal > intercostal > caudal/epidural > peripheral nerves > subcutaneous

Question 28

What effect does adding epi to LAs have? What about NaHCO3?

Answer 28

Adding epi will decrease the amount of systemic absorption because it causes vasoconstriction, but it also makes the environment more acidic which will slow the onset of action.

If you also add bicarb, it will speed the onset of action. With the combination of the two, you will improve the quality of the block and prolong the duration of blockade.

Question 29

Which areas of the body should use of epi in the LA be avoided?

Answer 29

fingers, toes, penis, nose

Question 30

What is the only LA that causes vasoconstriction?

Answer 30

cocaine

Question 31

Is metabolism of ester or amide LAs faster? How are they each metabolized?

Answer 31

Esters are faster - they are rapidly metabolism by pseudocholinesterase (ester hydrolysis)

Amides - Metabolized in liver – much slower than with esters

Question 32

T or F. There is no pseudocholinesterase in CSF and therefore the duration of a block with ester LAs and the termination of action depends on their absorption into the bloodstream.

Answer 32

true

Question 33

Why is it important to know if your patient has abnormal pseudocholinesterase activity?

Answer 33

They would be at increased risk of LA toxicity with ester LAs

Question 34

Which group of LAs (esters or amides) is an allergic reaction more common? Which 2 LAs in that group is it most common with?

Answer 34

Esters. Esters are derived from PABA – can be allergic to the production of this metabolite

Procaine/benzocaine -> PABA -> allergic reaction

Question 35

What are the CNS signs of LA toxicity?

Answer 35

Circumoral / tongue numbness, dizziness, tinnitus, blurred vision

Restlessness, agitation, nervousness, slurred speech, drowsiness, loss of consciousness

Muscle twitching, seizures

Question 36

How do you treat the CNS signs of LA toxicity?

Answer 36

Treat with benzodiazepines (caution with thiopental, propofol)

Question 37

cauda equina syndrome is associated with what?

Answer 37

Repeated doses of intrathecal lidocaine or tetracaine

Question 38

What is TNS and what is it associated with?

Answer 38

TNS (transient neurologic symptoms) with intrathecal 5% lidocaine - Slight to severe pain in buttocks and legs starting within 24 hours after anesthesia, lasting up to 10 days

Question 39

What are the Cardiovascular signs of LA toxicity?

Answer 39

Depress contractility, automaticity, conduction velocity

Also causes smooth muscle relaxation -> hypotension - Can lead to cardiac arrest

Question 40

How do you treat cardiovascular signs of LA toxicity?

Answer 40

Treat: ACLS, pressors - Avoid lidocaine, limit epi -

Intralipid to reverse cardiotoxicity - May require CPB (bypass)

Question 41

Which LA is considered most cardiotoxic?

Answer 41

IV bupivacaine – it avidly blocks cardiac Na
channels – difficult resuscitation

Can also cause vasodilation and inhibition of sympathetic reflexes

Question 42

Methemoglobinemia: Most common with ___ or ___ metabolites, but possible with ____.

Answer 42

prilocaine or benzocaine but possible with lidocaine

Question 43

What symptoms indicate met-Hgb >10%?

Answer 43

shortness of breath, cyanosis, mental status changes, headache, fatigue,
dizziness, loss of consciousness

Question 44

What symptoms indicate met-Hgb >50%?

Answer 44

dysrhythmias, seizures, coma and death

Question 45

What is used to treat methemoglobinemia?

Answer 45

methylene blue

Question 46

Symptoms of methemoglobinemia are more common in patients with what comorbidities?

Answer 46

anemia, cardiovascular disease, lung disease, sepsis, or other Hgb abnormalities hemoglobin species

Question 47

What is the max dose of marcaine?

Answer 47

Marcaine = Bupivacaine

Max dose in (mg/kg)
2 w/o epi
3 w/ epi

Question 48

What is the max dose of lidocaine?

Answer 48

Max dose in (mg/kg)
4.5 w/o epi
7 w/ epi

Question 49

What is the max dose of Naropin?

Answer 49

Naropin = Ropivacaine

Max dose in (mg/kg)
2 w/o epi
3 w/ epi