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Local Anesthetics
Local Anesthetics
85
Medical
Graduate
08/07/2015

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Term
how are ester local anesthetics eliminated
Definition
via metabolism by plasma cholinesterase. Except for cocaine which is eliminated in the liver.
Term
The most toxic ester LA is? Why?
Definition
Tetracaine is most toxic b/c it is metabolized the slowest out of all the esters
Term
Which lcoal anesthetic is least toxic? Why
Definition
Chloroprocaine since it is eliminated the FASTEST.
Term
When should chloroprocaine, tetracaine and procaine not be administered to apatient
Definition
Since all these ester LA are eliminated via plasma cholinesterase then anyone with a deficiency in plasma cholinesterase should not get them.
Term
which ester LA is not eliminated via plasma choilnesterase
Definition
cocaine
Term
what is the local agent that produces vasoconstriction
Definition
cocaine
Term
How are amides eliminated
Definition
via liver metaboilsm
Term
What the least toxic amide local anesthetic
Definition
prilocaine
Term
What is the max dose of lidocaine for a 70 kg patient without epi
Definition
500 mg
Term
which amide is most cardiotoxic and why
Definition
Bupivacaine is most cardiotoxic. R/T its more intense binding to gated Na channels.
Term
what is the difference of ropivicaine and bupivicaine
Definition
ropivicaine and bupivicaine are both long acting, similar pKa, protein bindnig, potency, and clinical use. The difference is that ropivicaine is less cardiotoxic and produces LESS motor block. (which makes ropivicaine better for labor patients)
Term
what is pKa
Definition
the pKa is the pH at which 50% of a weak acid or weak base is ionized and 50% is un-ionized.
Term
The local anesthetics are prepared as what kind of salts
Definition
hydrochloride salts
Term
Are local anesthetics weak acids or weak bases
Definition
weak bases
Term
what LA with this kind of pKa ___ be the most IONIZED at physiological pH of 7.4
Definition
a high pKA will be mostly ionized at a pH of 7.4.
Term
typically LA injected into body are in the ionized or un-ionized form?
Definition
Ionized! B/c Most pKas are higher than the body's pH therefore they become ionized.
Term
if LA is injected into an aeaa of trauma or infection will its onset increase or decrease or no effect? Why?
Definition
Decrease onset b/c prevailing acidosis increases the ionization of the LA.
Term
how does adding bicarb to LA increase its onset
Definition
bicarb is alakaline and addign it to local makes more un-ionized LA. This form of LA will be more likely to cross axon membranes to produce its affects.
Term
How does a local anesthetic work
Definition
They produce a conduction blockade of neural impulses in the affect nerve. This is accomplished by preventing passage of Na ions through ion-selective Na channels. By slow the rate of depolarization you prevent threshold from being reached.
Term
what state of the Na-Ion channel do Local anesthetics have the highest affinity to bind to
Definition
1. activated state
2. inactivated states.

Those conformations are most susceptible to LA binding.
Term
what is myelin (which surrounds the nerves) made up of
Definition
myelin is made from specialized schwanna cells that wrap around the axon. Myelin's purpose is:
1. insulation
2. increases speed of conduction.
Term
How many Nodes Ranvier are needed to be blocked in order for an effected LA administration
Definition
3x nodes of Raniver
Term
which is more sensitivt to LA
1. myelinaed nerves
or
2. unmyelinated
Definition
Myelinated nerves are more sensitive than nonmyelinated like C fibers
Term
which LA seems to be more selective for motor blockade versus sensory
Definition
etidocaine
Term
Most local Anesthetics have pKa that are
Definition
>7.4
Term
the primary determinant of potency for local anesthetics is
Definition
its lipid solubility
Term
in order from highest to lowest, what is the realtive order of peak plasma concentrations at
1. intercostal
2. sciatic/femoral
3. brachial plexus
4. caudal
5. epidural
Definition
Intercostal > caudal > epidural > brachial plexus > sciatica/femoral.
Term
What are the INITIAL manifestations of LA toxicity
Definition
1. circumoral numbness
2. facial tingling
3. restlessness
4. vertigo
5. tinnitus
6. slurred speech
Term
what are two mechanisms of action on how LA may cause hypotension
Definition
1. direct depression to the myocardium
2. relaxation of the peripheral smooth muscle
Term
what changes on the ECG may you see with LA toxicity
Definition
increase conduction time therefore increase PR and increase QRS. BC lidocaine is a class Ib antidys which causes early repolarization.
Term
what properties of bupivicaine that makes it a long acting LA
Definition
Its fast in, but slow out.
Term
the maximum recommended concentration of bupivicaine for epidural aneshtesia in obstetrics is
Definition
0.5% because 0.75 is associated with more s/e
Term
which local is associated with methemoblobinemia
Definition
prilocaine, lidocaine and benzocaine
Term
how do you treat methemoglobinemia
Definition
methylene blue
Term
what is transient neurologic symptoms (TNS)
Definition
is a syndrome of pain/dysesthesia in the lower back, posterior thighs, or buttocks that generally occurs within 24 hours of recovery from a spinal anesthetic.
Term
Is TNS associated with sensory loss, motor weakness or bowel or bladder dysfunction?
Definition
NOOOOOOOOOO this is not cauda equina syndrome
Term
Name the three risk factors for transient neurologic symptoms TNS
Definition
1. lidocaine use
2. lithotomy position
3. outpatient status
Term
cauda inquina syndrome is the result of damage to
Definition
nerve roots caudal to the conus.
Term
describe the SX of cauda equina syndrome
Definition
1. perineal sensory loss
2. bowel dysfunction
3. bladder dysfunction
4. lower extremity muscle weakness
Term
what are the chances for a true allergic reaction to local anesthetic
Definition
<1 %!! SO RARE for a true allergic reactions.
Term
IF true allergic reactions are rare to LA than why do people have reactions
Definition
RX TO metabolites.
Term
Why do ester LA have higher incidence of allergic reactions
Definition
due to metabolite known as PABA. Para-aminobenzoic acid
Term
what perservativie in LA may cause allergic reactions
Definition
preservative methylparaben
Term
the ester with the least potency
Definition
procaine
Term
least toxic ester and why
Definition
chloroprocaine since it is eliminated faster than all other local anesthetics.
Term
cocaine is an ester of what group?
Definition
benzoic acid
Term
why is bupivicaine most cardiotoxic
Definition
binds to gated sodium channels with great intensity.
Term
does ropivicaine or bupivicaine produce less motor blockade
Definition
ropivicaine. So better choice for pregnant people in labor.
Term
when would you expect a decrease in clearance of amide local anesthetics
Definition
1. decrease liver blood flow states
2. inhibtion of hepatic cytochrome p450 system.
Term
what is EMLA cream?
Definition
a combination cream made up of lidociane 2.5% and prilocaine 2.5%
Term
local anesthetics are prepared as what kind of salts
Definition
hydrochloride salts. lidocaine hydrochloride as an example.
Term
target range for local anesthetics is
Definition
7.6 to 9.1
Term
are local anesthetics weak bases or weak acids
Definition
weak bases
Term
do locals become more or less ionized as the pH increases.
Definition
Local are weak bases. AS pH goes up then Base + base = non-ionized.
Term
what local anesthetics, those with high pKa or low Pka are most ionized at physiological pH (7.4)
Definition
Those with Highest pKa are most ionized at pH of 7.4
Term
if a local is injected into an area of infection will it speed or slow onset
Definition
SLOW bc acidosis increases ionization of local
Term
what are some drugs that may decrase clearance of amide local anesthetics? Remember how do amides get cleared?
Definition
Amides are cleared via oxidation and the P450 system in the liver. Drugs such as
1. volatiles
2. propanolol
3. Cimetidine

ALL INHIBIT P450 or reduce blood flow and therefore increase duration of amide locals.
Term
why are preservative contianing solutions of local anesthetics not used for neuroaxial anesthesia
Definition
First of all preservatives in LA such as paraben family are highly culpable in allergic reactions. Secondily if used for neuraxial anesthesia they ARE NEUROTOXIC
Term
which two local anesthetics are administered as racemic mixtures?
Definition
bupivicaine and mepivcaine.
Term
what are the three stages of fast, voltage gated sodium channels
Definition
1. closed
2. open
3. inactivated
Term
what part of the nerve cell is actually the site of action for local anesthetics
Definition
THE AXON. Thats whats lined with Fast, voltage gated Na receptors. The soma and nerve endings is different.
Term
Since lipid solubility determines potency of a local anesthetic then what characteristic of the local is making it more lipid soluble
Definition
More carbon atoms than MORE lipid soluble THEN more POTENT.
Term
What six factors determine the absorption of local anesthetic into the surrounding vasculature and therefore increasing blood levels
Definition
1. Total Dose
2. pH
3. Use of vasoconstrictor
4. Amt of blood flow to that area
5. Lipid solubility of the agent
6. Protein binding of agent.
Term
What kind of pH would influence MORE local anesthetic levels in blood (toxicity)
Definition
The higher the pH means more non-ionized local. = more local getting absorbed into blood stream and causing toxicity.
Term
The greater or lower lipid solubility will result in faster blood levels and toxicity
Definition
Lower solubility b/c less drug in lipophilic tissues and instead will go into hydrophillic which is blood.
Term
which local anesthetic has the least protein binding
Definition
Chloroprocaine. HEnce why its so fast acting b/c none of it remains on proteins to slowly come off and keep localizing the area.
Term
speed of onset of a local anesthetic is determined by?
Definition
degree of ionization.
Term
what is the max dose of epi for use with a local anesthetic for infiltration, brachial plexus, epidural, caudal or intrapleural anesthesia
Definition
200-250 mcg
Term
the opitmal epi concnetration in a local anesthetic is
Definition
1:200,000
Term
1:100,000 is how many epi per mL
Definition
10 mcg epi PER 1 mL
Term
1:200,000 of epi is how much epi per mL
Definition
5 mcg epi per 1 mL
Term
how does prilocaine convert Hb to methemoglobin
Definition
prilocaine, an amide local anesthetic, is metabolized to orthotoluidine. Orthotouidine is an oxidizing agent capable of converting Hb tgo methemoglobin.
Term
what is methemoglobin
Definition
Oxidization of Hb which really means oxidizing of the Fe 2+ component to Fe 3+ makes it incapable of carrying oxygen.
Term
name two active metabolites of lidocaine
Definition
1. monoethylglycinexylidide (MEGX)
2. glycine xylidide (GX)
Term
The most susceptible fibers to local anesthetic blockade are?
Definition
Type B
Term
What is the menumonic for what sensory / motor elements are blocked by LA in order
Definition

ATP, TP, MVP ATP:

or AUdrey TEll PAul TO PRay for MOre VIagra PRoducts 

 

Autonomic - Temperature - Pain TP: Touch - Pressure MVP: Motor - Vibratory - Propioception.

Term
Name the three main chemistry components of a local anesthetics
Definition
Aromatic ring - intermediate linkage which is either an amide or ester - terminal amine.
Term
metabolism of esters result in what metabolite
Definition
PABA
Term
name in order where LA get absorbed the fastest in what tissue areas
Definition
tracheal > intrapleural > intercostal > caudal > epidural >
brachial (or other major nerve) plexus > intradermal > spinal
Term
A faster onset would be expected from a pKa of a LA that is closer or futher from physiologic pH
Definition
closer. so pKa of 7.9 would be faster onset than a pKa of 8.4.
Term
pKa of LIdocaine, chloroprocaine, and bupivicaine
Definition
1. lidocaine 7.9
2. Chloroprocaine 8.7
3. Bupivicaine 8.1
Term
Main determinant of duration of action of a LA is? Second component of DOA of action of LA is?
Definition
1. Protein binding #1
2. Lipid solubility #2
Term
name long acting LA
Definition
you can BET on them
Bupivicaine
Etidocaine
T: Tetracaine
Term
what local has a respiratory side effect of blunting ventilatory drive to hypoxemia
Definition
lidocaine
Term
early Sx of digoxin toxicity are? What should the therapuetic levels be?
Definition

Early Sx of digoxin toxciity are Anorexia, nausea, and vomiting. 

 

Digoxin levels should be < 0.5ng/L 

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