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Anesthesia Pharmacology > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

What is the mechanism of local anesthetics?

A

LA block voltage gated sodium channels preventing the influx of sodium ions, thus preventing an action potential

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2
Q

Local anesthetics bind Na channels in the _______ state

A

activated

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3
Q

How do local anesthetics affect resting and threshold potentials?

A

not altered

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4
Q 
Which nerves are more easily blocked?
Myelinated or unmyelinated?
small or large fibers?
resting or rapidly firing channels?
proximal or distal?
A 
Easier:
Myelinated
Small
rapidly firing
proximal
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5
Q

What are the three groups in the LA molecule?

A

Lipophilic group (benzene ring) and hdyrophilic group (tertiary amine) linked together with either an ester or amide

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6
Q

Name the amide LAs

A 
Lidocaine
mepivacaine
Prilocaine
Bupivacaine
Ropivacaine
Etidocaine
i before the caine
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7
Q

Name the ester linked LAs

A 
Procaine 
Chloroprocaine
tetrocaine
cocaine
benzocaine
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8
Q

Where are the amides metabolized?

A

liver

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9
Q

Where are esters metabolized? Exception?

A

esters are metabolized by plasma cholinesterases, except cocaine which is met in liver

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10
Q

Which are more potent, esters or amides? What determines potency?

A

Esters are more potent. Potency determind by lipid solubility

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11
Q

what properties determine onset?

A

lipid solubility and pKa

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12
Q

What is the measure of local potency for LA that is similar to MAC?

A

Cm

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13
Q

What factors determine the absorption of LA?

A 
Dosage
Site of injection
Drug-tissue binding
Local blood flow
vasoconstrictors
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14
Q

What side effect can metabolites of prilocaine and benzocaine have?

A

methemoglobinemia (ortholuidine)

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15
Q

What is the metabolite of esters that may cause an allergic rxn?

A

para aminobenzoic acid (PABA)

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16
Q

What is the physiologic effect of methemoglobinemia?

A

decreases O2 and CO2 carrying capacity of hemoglobin

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17
Q

Which group of pts have a higher risk for methemoglobinemia?

A

neonates due to fetal hemoglobin

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18
Q

What is normal methemoglobinemia?

A

<1%

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19
Q

What are the S & S of methemoglobinemia?

A

SOB
cyanosis
chocolatey-brown arterial blood
pulse ox that always reads 85%

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20
Q

What is the treatment for methemoglobinemia?

A

1-2 mg/kg methylene blue

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21
Q

Does addition of vasoconstrictors affect onset of LA?

A

no

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22
Q

Vasoconstrictors _________ duration of LA by limiting systemic _________ and maintaining the drug concentration at the _______.

A

increases
absorption
nerve

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23
Q

Addition of epi (increases/decreases) the chance of systemic toxicity?

A

decreases

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24
Q

What is concentration of epi used with LA?

A

1:200,000 or 5 mcg/ml

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25
How much does epi prolong the effect of bupivicaine?
epi has very little effect with bupivicaine
26
what factors influence the possibility of absorption leading to systemic toxicity?
Dose Vascularity of site presence of epi properties of the drug
27
Subcutaneous, intravenous, sciatic, tracheal, intercostal, brachial plexus, caudal, epidural paracervical. Arrange from most to least vascular
intravenous>tracheal>intercostal>caudal>paracervical>epidural>brachial plexus>sciatic>subcutaneous
28
What effects does systemic toxicity have on CNS?
Circumoral numbness Restlessness slurred speech siezure
29
What effects does systemic toxicity have on the cv system?
Hypotension Decreased cardiac conduction Ventricular arrythmias
30
Which has worse effects on the CV system? lidocaine or bupivicaine?
bupivicaine
31
What is the limit for dosages for lidocaine?
5mg/kg/ without epi | 7mg/kg with epi
32
What is the limit of the dose of bupivicaine?
2.5 mg/kg
33
What is the method of action of cocaine?
aside from its local effect cocaine also blocks reuptake of dopamine and norepi
34
How is cocaine used clinically?
mostly in ENT surgery for the nose due to its vasoconstrictive and local effects
35
What is the peak time of intranasal cocaine?
30-45 minutes
36
What are the adverse effects of cocaine?
increased HR, ventricular arrhythmias, and coronary vasoconstriction
37
How do you treat the toxicity of cocaine?
Supportive treatment | nitroglycerine
38
Is ephedrine a good choice for a chronic cocaine user?
No. Norepi stores will be depleted so ephedrine won't work
39
How long does lidocaine last in a spinal?
<1.5 hours
40
What is the side effect of lidocaine in a spinal?
transient neurological symptoms
41
What is a usual concentration of lidocaine for a spinal?
5% with 7.5% dextrose
42
How long does bupivicaine last in a spinal?
2-2.5 hours
43
What is a usual concentration of bupivicaine used for a spinal?
0.5% and 0.75% with or without dextrose
44
How long does tetracaine last in a spinal?
2-3 hours up to 5 with epi
45
What is the usual concentration of tetracaine used for a spinal?
1% solution, can be mixed with 10% dextrose
46
When and how does epidural anesthesia during deliveray become a problem for the neonate?
When the baby is in distress, it will become acidotic which traps the drug. toxicity may become a problem, esp with lido
47
What is the differences in volume used for epidural vs spinal?
Spinal usually uses 1-2 ml (up to 3-4 with bupivicaine according to the chart in the notes) while epidurals require 15-30ml
48
How is the duration of a bier block determined?
tourniquet time
49
How much 5% lidocaine or prilocaine would you use for a bier block?
50 cc
50
Which has a lower plasma concentration in a bier block at the same dose, prilocaine or lidocaine?
prilocaine
51
How much bupivicaine do you use for a bier block?
don't use bupivicaine for a bier block, more likely to cause cardiac effects when tourniquet is deflated
52
The _______ of the drug determines the amount of local anesthetic that exists in the nonionized form in the tissue
pKa
53
Which drugs are used for topical anesthesia?
prilocaine,cocaine, lidocaine (w/ oxymetazoline
54
What is local infiltration?
Extravascular placement of local anesthetic in the area to be anesthetized
55
What anesthetic is in hurricane spray?
benzocaine
56
Name a procedure where nebulized lidocaine may be used?
awake bronchoscopy
57
What is emla?
eutectic mixture of local anesthetic (a cream that is put on the skin and held there with a tegaderm)
58
What is the impediment that makes it difficult for local anesthesia to cross skin
keratin in the skin
59
How long is the onset and duration of emla?
1 hour, duration ~ 2 hrs
60
What is the dose for emla?
1-2 gram/10cm2 area of skin
61
Which patient is contraindicated for emla?
<1mo
62
Can a patient use an emla if they are susceptible to methemoglobin?
yes, just don't use prilocaine or benzocaine in the preparation
63
How much EMLA do you use for broken skin?
Don't use on broken skin
64
Which drugs are considered short acting for infiltration anesthesia?
procaine-20-30 min | Chloroprocaine 15-30 min
65
Which drugs are considered moderate duration for infiltration anesthesia?
Lidocaine-30-60 min Mepivacaine 45-90 min prilocaine 30-90
66
Which drugs are long acting for infiltration anesthesia?
Bupivacaine 120-240 min | Endocaine 120-180 min
67
What are the first 4 symptoms of local anesthetic toxicity?
circumoral numbness tinnitius lightheadedness visual disturbances
68
What are the last 5 symptoms of LA toxicity?
``` Muscle twitching Unconsciousness convulsions Respiratory depression cardiovascular collapse ```

Anesthesia Pharmacology (25 decks)

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