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
