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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
Q

How much does epi prolong the effect of bupivicaine?

A

epi has very little effect with bupivicaine

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26
Q

what factors influence the possibility of absorption leading to systemic toxicity?

A

Dose
Vascularity of site
presence of epi
properties of the drug

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27
Q

Subcutaneous, intravenous, sciatic, tracheal, intercostal, brachial plexus, caudal, epidural paracervical. Arrange from most to least vascular

A

intravenous>tracheal>intercostal>caudal>paracervical>epidural>brachial plexus>sciatic>subcutaneous

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28
Q

What effects does systemic toxicity have on CNS?

A

Circumoral numbness
Restlessness
slurred speech
siezure

29
Q

What effects does systemic toxicity have on the cv system?

A

Hypotension
Decreased cardiac conduction
Ventricular arrythmias

30
Q

Which has worse effects on the CV system? lidocaine or bupivicaine?

A

bupivicaine

31
Q

What is the limit for dosages for lidocaine?

A

5mg/kg/ without epi

7mg/kg with epi

32
Q

What is the limit of the dose of bupivicaine?

A

2.5 mg/kg

33
Q

What is the method of action of cocaine?

A

aside from its local effect cocaine also blocks reuptake of dopamine and norepi

34
Q

How is cocaine used clinically?

A

mostly in ENT surgery for the nose due to its vasoconstrictive and local effects

35
Q

What is the peak time of intranasal cocaine?

A

30-45 minutes

36
Q

What are the adverse effects of cocaine?

A

increased HR, ventricular arrhythmias, and coronary vasoconstriction

37
Q

How do you treat the toxicity of cocaine?

A

Supportive treatment

nitroglycerine

38
Q

Is ephedrine a good choice for a chronic cocaine user?

A

No. Norepi stores will be depleted so ephedrine won’t work

39
Q

How long does lidocaine last in a spinal?

A

<1.5 hours

40
Q

What is the side effect of lidocaine in a spinal?

A

transient neurological symptoms

41
Q

What is a usual concentration of lidocaine for a spinal?

A

5% with 7.5% dextrose

42
Q

How long does bupivicaine last in a spinal?

A

2-2.5 hours

43
Q

What is a usual concentration of bupivicaine used for a spinal?

A

0.5% and 0.75% with or without dextrose

44
Q

How long does tetracaine last in a spinal?

A

2-3 hours up to 5 with epi

45
Q

What is the usual concentration of tetracaine used for a spinal?

A

1% solution, can be mixed with 10% dextrose

46
Q

When and how does epidural anesthesia during deliveray become a problem for the neonate?

A

When the baby is in distress, it will become acidotic which traps the drug. toxicity may become a problem, esp with lido

47
Q

What is the differences in volume used for epidural vs spinal?

A

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
Q

How is the duration of a bier block determined?

A

tourniquet time

49
Q

How much 5% lidocaine or prilocaine would you use for a bier block?

A

50 cc

50
Q

Which has a lower plasma concentration in a bier block at the same dose, prilocaine or lidocaine?

A

prilocaine

51
Q

How much bupivicaine do you use for a bier block?

A

don’t use bupivicaine for a bier block, more likely to cause cardiac effects when tourniquet is deflated

52
Q

The _______ of the drug determines the amount of local anesthetic that exists in the nonionized form in the tissue

A

pKa

53
Q

Which drugs are used for topical anesthesia?

A

prilocaine,cocaine, lidocaine (w/ oxymetazoline

54
Q

What is local infiltration?

A

Extravascular placement of local anesthetic in the area to be anesthetized

55
Q

What anesthetic is in hurricane spray?

A

benzocaine

56
Q

Name a procedure where nebulized lidocaine may be used?

A

awake bronchoscopy

57
Q

What is emla?

A

eutectic mixture of local anesthetic (a cream that is put on the skin and held there with a tegaderm)

58
Q

What is the impediment that makes it difficult for local anesthesia to cross skin

A

keratin in the skin

59
Q

How long is the onset and duration of emla?

A

1 hour, duration ~ 2 hrs

60
Q

What is the dose for emla?

A

1-2 gram/10cm2 area of skin

61
Q

Which patient is contraindicated for emla?

A

<1mo

62
Q

Can a patient use an emla if they are susceptible to methemoglobin?

A

yes, just don’t use prilocaine or benzocaine in the preparation

63
Q

How much EMLA do you use for broken skin?

A

Don’t use on broken skin

64
Q

Which drugs are considered short acting for infiltration anesthesia?

A

procaine-20-30 min

Chloroprocaine 15-30 min

65
Q

Which drugs are considered moderate duration for infiltration anesthesia?

A

Lidocaine-30-60 min
Mepivacaine 45-90 min
prilocaine 30-90

66
Q

Which drugs are long acting for infiltration anesthesia?

A

Bupivacaine 120-240 min

Endocaine 120-180 min

67
Q

What are the first 4 symptoms of local anesthetic toxicity?

A

circumoral numbness
tinnitius
lightheadedness
visual disturbances

68
Q

What are the last 5 symptoms of LA toxicity?

A 
Muscle twitching
Unconsciousness
convulsions
Respiratory depression
cardiovascular collapse

Anesthesia Pharmacology (25 decks)

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