Local anesthesia Flashcards
what are the disadvantages of spinal block?
time limited, no titration, not reversible
where is a spinal block administered?
into CSF in lumbar subarachnoid space to reach spinal roots
what are the advantages of an epidural block?
not time limited, can be used 4-7 days post-op, titratable
what is the disadvantage of an epidural block?
less reliable block compared to spinal
what is the primary mechanism of action of local anesthetics?
blockage of voltage gated sodium channels - inhibits depolarization and repolarization
biotoxins act at what site?
external sodium channel
lidocaine acts at what site?
internal sodium channel
benzocaine acts at what site?
embed in lipid bilayer in vicinity of receptor and disrupt geometry of lipid bilayer - causes receptor to lose conformation and function
local anesthetics exist in what two forms?
protonated and non-protonated form
which form of local anesthetics get through the membrane?
non-protonated
which form of local anesthetics bind to the internal portion of the sodium receptor?
protonated
how are local anesthetics characterized chemically?
weak bases
what are the amide local anesthetics?
- lidocaine
- articaine
- bupivacaine
- ropivacaine
have two “i”s
what are the ester local anesthetics?
- cocaine
- procaine
- benzocaine
- tetracaine
- chloroprocaine
have one “i”
what is the most active form of local anesthetic at the sodium receptor?
cationic (protonated)
which has a longer half life - amide or ester local anesthetics? why?
amides - metabolized in liver
what are the factors that influence LA onset and recovery?
- fiber size
- site of deposition
- pH
- nerve stimulation rate
- calcium concentration
which fiber size is most sensitive?
small
are myelinated or nonmyelinated fibers more sensitive?
myelinated
in terms of blocking, which fibers are blocked first? last?
first - beta fibers
last - A alpha
how does pH influence minimum anesthetic concentration?
high pH - lower Cm
which nerve frequency is more sensitive - high or low?
high
how does calcium influence minimum anesthetic concentration?
increased calcium concentration - increased Cm
which drug is used as a vasoconstrictor to reduce systemic absorption and increase duration of LA action?
EPI
what are the factors that affect reversal of LA?
- dilution by ECF
- absorption into circulation
- redistribution to other areas
- use of vasoconstrictors
what is the most important factors affecting reversal of LA?
absorption into circulation
where are amide LAs metabolized?
liver
where are ester LAs metabolized?
plasma
amide LAs are metabolized to what chemical compound?
inactive metabolite
ester LAs are metabolized to what chemical compound? what is the clinical significant?
inactive metabolite - PABA moiety
prone to allergic reactions
patients who are allergic to ester LAs are actually allergic to what specific compound?
methylparaben (perservative)
are amide or ester LAs more prone to systemic toxicity? why?
amides - circulate in blood until metabolism in liver (longer half life too)
which LA has systemic toxicity that targets the heart?
bupivicaine
what is the treatment for LAST (LA toxicity)? what does it do?
IV lipid emulsion (IntraLipid) - forms a lipid sink to absorb circulating lipophilic toxin
which amide LA can be given both topically and IV?
lidocaine
what are the main clinical uses for bupivicaine?
- epidural transfusion used for labor analgesia and post-op pain
- excellent spinal anesthetic
what is the primary use for articaine?
dental anesthetic
what is the main clinical use of cocaine?
topical anesthetic for ENT procedures
what is the primary use for benzocaine?
topical use only due to enhanced lipid solubility
what are the clinical uses for chloroprocaine? why?
epidural for labor anesthesia (C-section) due to lower risk of systemic toxicity or fetal exposure
what is exparel-liposome?
encased bupicicaine that provides relief for up to 72 hours
what is EMLA?
eutectic mixture of LA
mixture of high concentration of LAs in oil-water emulsions - lidocaine and prilocaine
use - topical anesthetic on intact skin
what is TAC? what is the use?
tetracaine - adrenalin - cocaine
topical in pediatric ERs