24 Local Anesthesia Flashcards
What are the key differences of local anesthetics from general anesthesia?
nerve blockade to eliminate SENSORY and MOTOR response to a surgical stimulus
What are the 2 classifications of local anesthetics?
Amide and ester
Where are the amides metabolized?
liver
Where are the esters metabolized or by what?
plasma esterases
Cocaine and benzocaine are used as what in local anesthesia?
topical esters
Amides have what in their name to help give you a clue?
an I before the caine
T-F–local anesthetics are more potent when they are lipid soluble?
true
Is procaine high potency?
No, low
Is mepivacaine and lidocaine intermediate potency?
Yes
Is tetracaine and bupivicaine low potency?
No, high
T-F–local anesthetics are protonated as a weak acid?
False–protonated but are weak bases
Where doe the protonated local anesthetic act?
Binds to the voltage gated Na channel from the intracellular space
Na influx is important for what in the nerve?
Initiation of action potential,
Small doses of lidocaine can give a good block?
False, need huge doses
A lot of locations for lidocaine on a nerve causes what?
scrambles the conduction
T-F–Esters pKa are lower that amides?
False
As tissue pH decreases the amount of local anesthetic in the nonionized form _________?
decreases
T-F–local anesthetics differ in duration of action>
True
How well do local anesthetics work in acidotic tissue? Outcome?
not very well
Drug cannot enter intracellular space and this is when toxicity can be a major concern
What is the henderson hasselbach equation as it relates to local anesthetics?
pH=pKa+log LA/LA+
[LA+=local anesthetic protonated]
What is the fraction of neutral local anesthetic to local anesthetic protonated of a drug at pH6.4 and a pka of 7.4?
What about a pH of 8.4?
LA/LA+ = 1/10
LA/LA+=10
T-F–local anesthetic drugs bind the extracellular Na channel portion blocking the depolarization and sensory/motor signals.?
False-intracellular
Which subclass [2] of nerve fibers are less sensitive (1/2 sensitive) to local anesthetics? What do they do?
Csymp–>autonomic functions
Csens–>pain, temp, touch
Nerve subclasses below have what functions? Aalpha=? Abeta? Agamma? Asigma? B?
alpha=motor/proprioception beta=motor/proprio/touch gamma=muscle tone sigma=pain/temp/touch B=autonomic functions
Is B or C symp nerve subclass preganglionic sympathetics?
B is. C is postganglionic sympathetics
With increasing plasma concentrations, what are the signs and symptoms of local anesthetic toxicity? [There are several, try climbing the latter]
Numb Tongue Lighthead vis/aud disturb Unconsciousness Convulsions Coma Respiratory Arrest Cardiac Toxicity
Does cardiac toxicity come before or after coma in regards to local anesthetic toxicity?
After
What type of administration technique of local anesthetic creates the highest plasma concentration levels and subsequently leads to greatest risk of toxicity?
Intercostal
[Then epidural and then subcutaneous]
What is used in conduction with local anesthetics to lower the systemic plasma concentration of the drug?
Epinephrine because of its vasoconstrictive actions
For local anesthetic toxicity what drugs do we give? [2]
Intralipid-intravenously
Also, barbiturates or benzodiazepines for seizures
Are esters or amides local anesthetics more likely to give an allergic reaction to ? [what are the major or more common culprits though?]
Esters
[Others are the EPI/preservatives and other drugs used]
Ester local anesthetics such as benzocaine for baby teeth have shown what dangerous side effect in children?
methemoglobinemia
What local anesthetic is most used for starting IV and minor surgeries?
1% lidocaine intra or subQ
What is the Bier Block?
Intravenous injection of anesthetic into extremity that has a tourniquet more proximal to injection
[surgeries up to 2 hours, may be useful for chronic pain]
How do we find the nerve for a femoral nerve blockade?
electrical stimulator
What are the 2 major peripheral nerve blockade for leg surgery?
Femoral and sciatic
What is the major toxicity/side effect we must always be concerned about with cocaine?
vasoconstrict—>MI
Is ropivacaine the s-isomer or r-isomer of a racemic mixture?
S
What is a common additive to increase basicity or create heaviness?
8.5% Dextrose
If epinephrine has a 1 to 200,000 ratio, what does this mean?
1 gram to 200,000ml
If I wanted to convert an epinephrine 1:200,000 to mcg/ml what would it be?
5mcg/ml
[1g/200,000ml—>1,000,000mcg/200,000ml—>5mcg/ml]
1% solution of lidocaine contains what g/ml? mg/ml?
1g/100ml
10mg/ml
