Local anesthesia

Question 1

what are the disadvantages of spinal block?

Answer 1

time limited, no titration, not reversible

Question 2

where is a spinal block administered?

Answer 2

into CSF in lumbar subarachnoid space to reach spinal roots

Question 3

what are the advantages of an epidural block?

Answer 3

not time limited, can be used 4-7 days post-op, titratable

Question 4

what is the disadvantage of an epidural block?

Answer 4

less reliable block compared to spinal

Question 5

what is the primary mechanism of action of local anesthetics?

Answer 5

blockage of voltage gated sodium channels - inhibits depolarization and repolarization

Question 6

biotoxins act at what site?

Answer 6

external sodium channel

Question 7

lidocaine acts at what site?

Answer 7

internal sodium channel

Question 8

benzocaine acts at what site?

Answer 8

embed in lipid bilayer in vicinity of receptor and disrupt geometry of lipid bilayer - causes receptor to lose conformation and function

Question 9

local anesthetics exist in what two forms?

Answer 9

protonated and non-protonated form

Question 10

which form of local anesthetics get through the membrane?

Answer 10

non-protonated

Question 11

which form of local anesthetics bind to the internal portion of the sodium receptor?

Answer 11

protonated

Question 12

how are local anesthetics characterized chemically?

Answer 12

weak bases

Question 13

what are the amide local anesthetics?

Answer 13

1. lidocaine
2. articaine
3. bupivacaine
4. ropivacaine

have two “i”s

Question 14

what are the ester local anesthetics?

Answer 14

1. cocaine
2. procaine
3. benzocaine
4. tetracaine
5. chloroprocaine

have one “i”

Question 15

what is the most active form of local anesthetic at the sodium receptor?

Answer 15

cationic (protonated)

Question 16

which has a longer half life - amide or ester local anesthetics? why?

Answer 16

amides - metabolized in liver

Question 17

what are the factors that influence LA onset and recovery?

Answer 17

1. fiber size
2. site of deposition
3. pH
4. nerve stimulation rate
5. calcium concentration

Question 18

which fiber size is most sensitive?

Answer 18

small

Question 19

are myelinated or nonmyelinated fibers more sensitive?

Answer 19

myelinated

Question 20

in terms of blocking, which fibers are blocked first? last?

Answer 20

first - beta fibers

last - A alpha

Question 21

how does pH influence minimum anesthetic concentration?

Answer 21

high pH - lower Cm

Question 22

which nerve frequency is more sensitive - high or low?

Answer 22

high

Question 23

how does calcium influence minimum anesthetic concentration?

Answer 23

increased calcium concentration - increased Cm

Question 24

which drug is used as a vasoconstrictor to reduce systemic absorption and increase duration of LA action?

Answer 24

EPI

Question 25

what are the factors that affect reversal of LA?

Answer 25

1. dilution by ECF 2. absorption into circulation 3. redistribution to other areas 4. use of vasoconstrictors

Question 26

what is the most important factors affecting reversal of LA?

Answer 26

absorption into circulation

Question 27

where are amide LAs metabolized?

Answer 27

liver

Question 28

where are ester LAs metabolized?

Answer 28

plasma

Question 29

amide LAs are metabolized to what chemical compound?

Answer 29

inactive metabolite

Question 30

ester LAs are metabolized to what chemical compound? what is the clinical significant?

Answer 30

inactive metabolite - PABA moiety prone to allergic reactions

Question 31

patients who are allergic to ester LAs are actually allergic to what specific compound?

Answer 31

methylparaben (perservative)

Question 32

are amide or ester LAs more prone to systemic toxicity? why?

Answer 32

amides - circulate in blood until metabolism in liver (longer half life too)

Question 33

which LA has systemic toxicity that targets the heart?

Answer 33

bupivicaine

Question 34

what is the treatment for LAST (LA toxicity)? what does it do?

Answer 34

IV lipid emulsion (IntraLipid) - forms a lipid sink to absorb circulating lipophilic toxin

Question 35

which amide LA can be given both topically and IV?

Answer 35

lidocaine

Question 36

what are the main clinical uses for bupivicaine?

Answer 36

1. epidural transfusion used for labor analgesia and post-op pain 2. excellent spinal anesthetic

Question 37

what is the primary use for articaine?

Answer 37

dental anesthetic

Question 38

what is the main clinical use of cocaine?

Answer 38

topical anesthetic for ENT procedures

Question 39

what is the primary use for benzocaine?

Answer 39

topical use only due to enhanced lipid solubility

Question 40

what are the clinical uses for chloroprocaine? why?

Answer 40

epidural for labor anesthesia (C-section) due to lower risk of systemic toxicity or fetal exposure

Question 41

what is exparel-liposome?

Answer 41

encased bupicicaine that provides relief for up to 72 hours

Question 42

what is EMLA?

Answer 42

eutectic mixture of LA mixture of high concentration of LAs in oil-water emulsions - lidocaine and prilocaine use - topical anesthetic on intact skin

Question 43

what is TAC? what is the use?

Answer 43

tetracaine - adrenalin - cocaine topical in pediatric ERs