local # 2 Flashcards
structure of local anesthetic
aromatic end, intermediate chain, amine end
amide
0=c-n-r
ester
0=c-or
infiltration long and short acting
bupivicaine long acting, tetracaine short acting
peripheral block long and short acting
short-lidocaine, long- bupivicaine
SAB long and short acting
short- idocaine/procaine, long- bupivicaine or tetracaine with epi
epidural long and short acting
long- bupivicaine or ropivicaine with epi, short chloroprocaine
mechanism of action of locals
inhibit na+ influx through na specific ion channels in neuronal cell membrane.
what must locals be to cross cell membrane and exert action?
non-ionized and lipophilic,then ionized binds to sodium channel
pka procaine and onset
8.9 onset- slow
tetracaine pka
8.6 slow onset
bupivicaine and ropivicaine pka
8.1, moderate onset
pka chloroprocaine
9.1, but fast onset
lidocaine/etidocaine pka
7.7, fast onset
mepivicaine pka
7.6 fast onset
decreased pka =
fast onset
problem with local toxicity is when
local gets into plasma
higher absorption
intercostal>caudal>epidural>brachial plexus>sciatic nerve
elimination of locals
prilocaine>etidocaine>lidocaine>mepivacaine>bupivacaine
what can be excreted ionized or unionized
unionized are not excreted
liver disease and metabolism locals
decreased blood flow, increased metabolism time
increased extracellular calcium does what to LA
antagonizes
what does increased extracellular potassium lead to
increased action locals
protein binding and bupivicaine, lidocaine and procaine
bupivicaine- 95%
lidocaine- 65%
procaine- 6%
protein binding deals with duration. greater protein binding, greater duration
cns signs early to late
circumoral numbness tongue paresthesia tinnitus blur vision/dizziness agitation slurred speech/unconcious seizures respiratory arrest/death
cardiovascular effects locals
depression of myocardial automaticity, abnormal pacer activity, decreased excitability, decreased contraction and conduction and arterial dilation
if sodium channels are completely closed what happens
absolutely nothing
which local is most toxic
bupivicaine
what is treatment for bupivicaine toxicity
lipids
respiratory effects of local
respiratory depression, decrease hypoxic drive, relaxation of smooth muscle, blok bronchospasm during intubation
allergies with amides
very rare- due to methylparaben (preservative)
allergies to esters
more common, due to PABA
what do you do if there is an allergic reaction
d/c drug, 100% o2, epi 0.01-0.5 iv/im fluids 1-2L benadryl hydrocortisone intubation
what can prilocaine levels greater then 10mg cause?
methemoglobinemia
cauda equina from
lidocaine spinal- neuronal damage
what channel is responsible for depolarization of neuronal cells?
voltage gated sodium channels
local anesthetics work
on inside of cell, no action on outer
weak bases will have more drug available
at ph higher then physiological, bases love bases
1% lidocaine
10mg/ml
2% lidocaine
20mg/ml
1:100,000 epi
10mcg/ml
1:200,000 epi
5mcg/ml
.1% lidocaine
1mg/ml
local anesthetic with pka closer to physiologic ph will have
greater concentration of nonionized base that can pass through nerve cell membrane and rapid onset
what must la be to cross membrane
uncharged to penetrate membrane, then ionized to chared binds
pka
50% unionized, 50% unionized at that ph
if ph is lower then pk
more ionized then unionized
if ph is higher then pka
more unionized
decreased ph equals
greater h+ concentration
