local anesthetics Flashcards
local anesthetics are drugs that ____ block the conduction of electrical impulses along nerve fibers
reversibly
axolemma
cell membrane surrounding an axon
axoplasm
intracellular contents
schwann cells
produce myelin sheath, support and insulation
myelinated
have electrically insulating layer
Nodes of Ranvier
gap in myelin sheath, speeds propagation of action potentials, do not contain myeline.
saltatory conduction
the propagation of action potentials along myelinated axons from one node to the next, increasing conduction velocity of action potential. jumping node to node
fasciculi
bundle of axons (nerve fibers
endoneurium
layer of delicate connective tissue around the myelin sheath of each fiber
perineurium
middle layer, consists of layers of flattened, overlapping cells, binds a group of fascilices together
epineurium
outermost layer, made of connective tissue, holds fasiculli together
myelinated vs unmyelinated
myelinated are larger, conduct impulses faster, and are more difficult to block with LA than unmyelinated
order of layers inner to outer
endo, peri, epi
resting potential voltage?
-70MV
Na reverses membrane potential to
+35mv
resting membrane potential is restored by
active removal of intracellular Na+ by the Na/K pump (3/2)
local anesthetics ___ action potential
slow down
a-b-c
A is biggest, then B, then C
the only unmyelinated fibers
C fibers
C fibers are for pain and temp,
smallest and slowest
where are receptors for LA’s located
intracellular side of cell membrane
the receptors have a greater affinity for what form of the local anesthetics?
charged, ionized
to first penetrate the cell membrane, must be
non-ionized, uncharged state. weak bases
La are ___ in the physiologic pH and ___ inside the cell
basic, acidic
the sodium channel exists in what 3 ways
resting (closed) , activated (open) , inactivated
LA binds more easily to Na channel when it is
activated (open) or inactivated
the ___ portion of the LA is what makes them different and have implicates for metabolism and allergic potential
linkage
esters and amides have ___ structure which helps maintain lipophilicity
ring
the ____ all have the letter I in them
amides
change in ____ = change in duration of action
lipid solubility
LA with a pKa closest to physiologic ph will have a ___ concentration of non-ionized form that can readily pass thru the nerve cell membrane
higher
ion trapping
weak base in a very acidic environment will convert and become ionized and not be able to pass into the axon
ion trapping happens with injection into
acidic, infected tissues
acidosis resulting from hypoxia may increase the ionized fraction of LA accumulation in
fetal circ
highly lipid soluble = ___ duration of action
longer. fat likes fat. less likely to be cleared by blood flow
onset of action isnt super variable among the LA’s but ___ is
duration
1% solution =
1g/100ml
all LA have ____ effects except for cocaine
vasodilatory
the higher the concentration of drug injected that remain in the area of the nerves to be blocked, the ____ the onset of action
faster
systemic absorption ___ from the tissue injection site results in the offset and termination of drug effect
AWAY
the closer an LA is injected to a site of blood flow, the ___ it will discipate
faster
the more fatty the area, the ___ the duration of action
longer
you can add in a vasoconstrictor like epi to decrease
vascular absorption. (limits side effects, prolongs duration, enhances quality, increases nerve cell uptake)
vasodilation from an LA ___ blood flow to the surrounding tissue where the drug is deposited
increases
vasodilatory effects cause ___ absorption, ____ duration of action, and ___ toxicity
increased , reduced, increased
greatest reservoir for LA?
muscle mass
esters are metabolized by ____
pseudocholinesterase
pseudocholinesterase do what
rapidly break down esters into water soluble metabolites that are excreted in urine (hydrophilic, ionized, kicked out by kidneys)
esters and allergic reactions!!!!
procaine and benzocaine are metabolized to PABA (p-aminobenzoic acid)
how are pt’s with genetically abnormal pseudocholinesterase at risk?
build up, longer duration, higher tox
how are amides metabolized
CYP 450 enzymes in liver
esters are metabolized ___ than amides
faster
rate of metabolism of amides
prilo > lido > mevicao, > ropiva > bup. (pink lads move ropes best)
decrease in liver function will reduce metabolism and increase toxicity of
amides
risk of amides
prilocaine metabolites covert hb to methemoglobin.
treat methemoglobinemia with
methylene blue
methemoglobinemia causes
grey cyanotic, met acidosis, reduced o2 carrying capacity, significant in anemic or heart failure patient
what two things influence toxicity greatly
absorption and metabolism
the ___ a local is absorbed into the vascular space, the ___ likely that high blood levels and CNS toxicity will occur
slower, less
what can you add to LA’s
opiates, sodium bicarb, epi
what causes systemic toxicity?
inadvertent intravascular injection, administration of excessive dose
cardiocirc tox.. first you see
htn tachy (matching vasodilatory effects)
cardiocirc tox.. second you see
brady, extrasystoles, hypotension
cardiocirc tox.. lastly you see
asystole
cerebral tox.. first you see
psych abnormal
cerebral tox.. second you see
confusion, dizziness, tinnitus, metalic taste
cerebral tox.. last you see
seizures
which system is more resistant to tox of LA
CV
all LA ___ myocardial automaticity and ____ duration of refractory period
depress, reduce
high blood levels of LA will __ contractility and conduction
depress
LA’s produce smooth muscle ___ and arteriolar ____
relaxation, vasodilation
which drug is known for cardio tox
bupivacaine
what can you give for cardio tox
lipid rescue 10-30% solution, binds up with other lipids
dysesthsia, burning, pain and aching in lower extremity and buttocks associated with
lido
eutectic mixture
topical , on intact skin. lipophilic
EMLA
lido and prilo. takes 1 hr
why shouldn’t you put topicals on thin mucous membranes or areas with lot of bloodflow
cause damage, tox, increased absoption
cocaine is used for
vasoconstriction for ENT cases
a fibers
large, myelinated, motor function and proprioception. not as sensitive.. need more LA.
B fibers
pregang autonomic nerves
C fibers
small, unmyelinated, slow. most susceptible to LA.
