Local Anesthetics Flashcards
Describe the mechanism of local anesthetic action in regional anesthesia. Classify local anesthetics based upon their chemical structure. Describe determinants of local anesthetic effects, compare/contrast the clinical effects of local anesthetics, and describe the impact of physiochemical properties of local anesthetics on local anesthetic potency, duration of action, and toxicity. Describe systemic and regional clinical manifestations of local anesthetic toxicity.
MOA of local anesthetics
bind to sodium channels to reduce na+ permeability and prevent attainment of APs
intermediate potency.short duration LA
chloroprocaine
low potency/intermediate duration LA
lidocaine
high potency/long duration LA
tetracaine
intermediate potency/long duration LA
bupivacaine
three main chemical components of LA
lipophillic (aromatic ring), linking hydrocarbon chain and ionizable component (possible amine)
amides
(2 “i”s) lidocaine, etidocaine, mepivicaine, bupvicane, ropivacaine
esters
only one “i” cocaine, chloroprocaine, tetracaine, cocaine
major uses of regional anesthesia
topical, local, peripheral nerve blocks, regional, major neuraxial blockade
chemical determinants of clinical effects
lipid solubility, protein binding, pKa,
primary determinnt of LA potency
lipid solubility
major determination of duration of action
lipid solubility
minor determination of LA duration
protein binding ability
LAs must be ____ to penetrate nerve membrane, but _____ to block Na+ channel
un-ionized/ionized
relation of pKa to onset speed
high pKa = slow onset. low pKa = faster onset
increased dose causes _____ duration,and intenstity, and _____ onset time
increased, decreased
reason for addition of vasoconstrictors to LA
slow onset, prolong duration by slowing distribution
nerves that are acted upon faster by LAs
smaller, mylerinated
types of nerves acted upon (in order)
pain -> temp -> touch -> pressure
additive to LA that shortens onset and prolongs duration
bicarb. facilitates diffusion through membranes by increasing extracellular pH and decreasing intracellular pH
continum of LA toxicity
tounge/periorbital numbness –> audio/visual disturbances –> muscle twitching and seziures - > CV collapse and death
last major sign of LA toxicity
CNS excitatiion followed by CV/CNS depression
dependant factors in LA toxicity
potency of drug, rate of injection, acid base status, site of administration (major site worse than minor)
decreases seizure threshold in LA toxicity
hypercarbia/acidocis
LA toxicity: which comes first? CNS tox or CV tox?
CNS
causes CNS tox long before CV tox
lidocaine
causes CV tox shortly after CNS tox
bupivacaine
increases suceptibility to bupivacaine tox
pregnancy
chemical type more likely to cause allergic reactions
amino-esters
reason amino-esters cause allergic reactions
metabolized to PABA derivatives
reported to cause lubmbosacral nerve root irritation
lidocaine and mepivacaine
risk factors for cauda equina syndrome from LA tox
high lidocaine concentrations and microbore spinal catheters
lidocaine may be no longer appropriate for ____ use
spinal use
used to treat LA toxicity
intralipid
Procaine uses
infiltratio and differential spinal anesthesia - used to diagnose pain sydromes
chloroprocaine uses
epidurals
problems with chloroprocaine
preservitives may cause neuro deficits or back pain
tetracaine use
spinal and topical anesthestic
LA that can be toxic bcause of rapid absportion w/topical dosing
tetracaine
benzocaine use
topical anesthesia only
cocaine use
potent vasoconstrictor (used in nasal procedures)
SE of cocaine
sympathetic ANS stimulation
Lidocaine use
topical, infiltration, nerve blocks, major blockade
mepivacaine use
infiltration, peripheral nerve block, major blockade
LA contraindicated in PB use because it slows fetal metabolism
mepivacaine
common dental anesthetic
mepivicaine
comminly used LA for OB use
bupivacaine
advantage of bupivicane in OB use
analgesia WITHOUT motor block
uses of ropivacaine
Labor, infiltration, peripheral nerve blockade, epidural
advantage of ropivicaine over bupivacaine
lower cardiac toxicity
LA that exists in pure S isomer
ropivacaine
