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► Med Misc 44 > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

Local Anesthetics:

what is the determinant for the speed of onset?

A

amount of LA in NON-Ionized form

AKA– the pKa

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2
Q

Local Anesthetics: Onset (pKa)
agents w/ ______ pKa are MORE NON-Ionized at a pH of 7.4. (the more non-ionized the faster it penetates the lipid bilayer.

A

LOWER

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3
Q

Local Anesthetics: Onset (pKa)

Agents w/ a high pKa have a _______ onset

A

slower onset

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4
Q

Local Anesthetics: Onset (pKa)

Agents with a low pKa have a _____ onset

A

faster

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5
Q

Local Anesthetics: Onset (pKa)

why is it that a lower pKa has a faster onset

A

bc if you remember the line and place the pKa on it it will be more non-ionized.
Also if pH is 7.4 and pKa is 9 then obviously less than 50% is non-ionized, but if pKa is 7.4 then 50% is non-ionized

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6
Q 
Local Anesthetics: Onset (pKa)
place these in order from slowest onset to fastest onset
Drug        pKa 
Procaine 8.9
Mepivacaine 7.6
Lidocaine 7.7
Tetracaine 8.6
Etidocaine 7.7
Ropivacaine 8.1
Bupivacaine 8.1
Chloroprocaine 9.1
A 
onset           % non-ionized (just to visualize)
Procaine 8.9       3        
Tetricaine 8.6      14
Bupivacaine 8.1    17
Ropivacaine 8.1    17
Chloraprocaine 9.1 2 (the one exception) fastest
Lidocaine 7.7        24
Etidocaine 7.7       33
Mepivacaine 7.6   39
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7
Q

Local Anesthetics: Onset (pKa)
in general, the LOWER the pKa of the LA, the greater the proportion of LA in the NON-IONIZED form at pH=7.4, and the _______ the onset of the conduction block.

A

faster

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8
Q

LA block nerve conduction by blocking (impairing) propagation of the action potential along axons. the block is accomplished by directly acting on _______ channels and inhibiting ____ influx

A

Sodium Channels

Na++

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9
Q

the ____ of the LA determines the speed of onset?

A

pKa

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10
Q

A LA that has a HIGH lipid solubility is very ____. Lipophilic LA more readily cross nerve membranes

A

potent

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11
Q

Local anesthetics the are highly ____ ____ will have a prolonged duration of action.

A

Protein Bound

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12
Q

pKa relates the what?
Lipid solubility relates to what?
Protein binding relates to what?

A

pKa - onset (low pKa fast onset)
Lipid solubility - potency (more lipid soluble more potent)
Protein binding - duration (more bound longer duration)

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13
Q

what is the determinant for potency?

A

lipid solubility

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14
Q

Local Anesthetics: Lipid Solubility (potency)

what is a good measure of lipid solubility?

A

oil:water partition coefficient

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15
Q

Local Anesthetics: Lipid Solubility (potency)

the greater the oil:water partition coefficient the ____ the lipid solubility

A

greater

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16
Q 
Local Anesthetics: Lipid Solubility (potency)
place in order from least to most potent
LA            Oil: water partition Coefficient
Etidocaine 140
Chloroprocaine 1
Mepivacaine 1
Tetracaine 80
Lidocaine 4.0
ropivacaine
A 
Drug  least potent to most potent
Chloroprocaine 1
Mepivacaine 1
Lidocaine 4
Tetracaine 80
Bupivacaine 30
Ropivacaine
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17
Q

Local Anesthetics: Lipid Solubility (potency)

explain the potency as it applies to our anesthetics like Lidocaine and Bupivacaine

A

Lido is less potent oil:water is 4.0. we need large amounts when we use it for ex usually comes in 1%, 2%, 4% etc
Bupivacaine is more potent, oil:water is 30. we need small amounts when we use it for ex usually comes in 0.25%, 0.5%, 0.75%

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18
Q

Local Anesthetics: Lipid Solubility (potency)

In general the more lipid soluble the LA the greater it’s _____

A

potency

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19
Q

what determines the duration of action of a LA

A

both protein binding and lipid solubility (but primarily we are concerned w/ protein binding)

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20
Q

Local Anesthetics: Duration of action

what is the MOST important factor in determining the duration of action of a LA

A

Protein binding

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21
Q

Local Anesthetics: Duration of action

the greater the protein binding the _____ the duration of action

A

longer

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22
Q

Local Anesthetics: Duration of action

how does protein binding control the duration of a LA

A

immediately after injection of LA, much of the agent binds to proteins in the vicinity of the injection site. as the unbound anesthetic diffuses from the injection site, some protein bound LA is released and becomes available to diffuse to nerve axons. thus proteins serve as storage depots for the LA

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23
Q

Local Anesthetics: Duration of action
so we already discussed that duration is primarily dependent on Protein binding, but what is the other factor that plays a role in duration of action?

A

Lipid solubility

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24
Q

Local Anesthetics: Duration of action

agents w/ greater lipid solubility tend to have ____ durations of action

A

longer

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25
Q

Local Anesthetics: Duration of action

How does lipid solubility control duration of action of a LA?

A

After the LA is injected some of it will dissolve in lipids in and around the site of injection. Agents w/ higher lipid solubility will dissolve to a greater extent in surrounding tissue (lipids). thus the lipid act as a reservoir for lipid soluble agents, just as proteins act as a reservior for agents that bind to proteins. As the LA diffuses away from the site of injection, LA will diffuse out of the lipid compartment down the concentration gradient and will act on the nerve to maintain he nerve block.

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26
Q

Local Anesthetics: Duration of action

what single change in property of a LA will result in more POTENT and LONGER acting agent?

A

an increase Lipid solubility. An Increase in lipid solubility will increase the duration of action and the potency

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27
Q

Weak Bases ( Benzos, LA, Opioids, Ketamine) bind to what protein?

A

Alpha 1 - glyco protein

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28
Q

Weak acids (thiopental, Propofol, barbiturates) bind to what protein?

A

Albumin

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29
Q

Local Anesthetics: Duration of action
the duration of action is greatest for LA that exhibit the greatest _______ and highest _____ . However ______ is more important when it comes to duration of action

A

Protein Binding and Lipid solubility

Protein binding

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30
Q

Determinants of blood concentration of LA:

blood concentration is determined by what 4 things

A

pressance or absence of vasoconstrictor
tissue blood flow
concentration of injection
number and frequency of injections

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31
Q

Determinants of blood concentration of LA:

loss of LA from injection site is primarily by what?

A

vascular absorption

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32
Q

Loss of LA from injection site is primarily by vascular absorption. the rate of absorption of LA from the injection site is influenced by what 2 things

A

Presence of vasoconstrictor

High blood flow to tissue

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33
Q

Determinants of blood concentration of LA:

what does the presence of a Vasoconstrictor to?

A

decreases the rate of absorption

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34
Q

Determinants of blood concentration of LA:

what does high blood flow to the tissue do

A

the greater the blood flow the faster the agent is absorbed into circulation and washed away from the site.
this higher blood flow = reduced duration of action

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35
Q

rank the bodies tissues from highest to lowest blood flow . Or think of it as what area or routes are where the most LA will be absorbed systemically into the blood circulation to the least

A 
IV
Tracheal
Intercostal
Caudal
Paracervical
Epidural
Brachial plexus
SA/ Sciatic/ femoral
Subcutaneous

Mnemonic I Think I Can Push Each Bolus SSlowly For Safety

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36
Q

Factors unrelated to Physoichemical Properties that prolong Block:
how does presence of vasoconstrictor prolong block

A

decreases blood flow and slows the removal of the LA

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37
Q

Factors unrelated to Physoichemical Properties that prolong Block:
how does concentration of LA prolong block

A

greater concentrations increase block duration

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38
Q

Factors unrelated to Physoichemical Properties that prolong Block:
how does blood flow prolong block

A

the lower the blood flow the slower the removal of LA

39
Q

Mechanism of Action of Local Anesthetics:

LA block what channels

40
Q

Mechanism of Action of Local Anesthetics:

what form of the LA diffuses into the nerve axon?

A

NON-ionized

41
Q

Mechanism of Action of Local Anesthetics:

what form of the LA binds to the receptors on the Na+ channel

42
Q

Mechanism of Action of Local Anesthetics:

explain how the LA works on the Na+ channel

A

this a LA (LAH+ LA + H+ ) the LAH+ breaks down in the body to LA + H+. the non-ionized part ( LA ) crosses the lipid bilayer into the nerve cell. there the LA binds with free floating H+ to again form an IONIZED for LAH+. the LAH + binds to the Na+ channel on the inside of the nerve axon.

43
Q

Must Know:

for mylinated axons __-__ nodes of ranvier must be blocked to stop nerve conduction

44
Q

Must Know:

conduction block if frequency dependent. explain that.

A

the greater the frequency of the action potential, the faster the nerve is blocked. B/c the LA must attach to the Na+ channel in the inactive state; the faster the nerve is firing, the more opportunities the LA will have to “catch” the Na+ channel in the inactive state

45
Q

Must Know:

is the ionized or non-ionized form of the LA needed to block nerve conduction?

A

both non-ionized and ionized forms are required for a conduction block

46
Q

Must Know:

Voltage gated Na+ channels are only found in the nerves ____

47
Q

____ block is 2-6 dermatomes HIGHER than the sensory block

A

Sympathetic

48
Q

____ block is 2 dermatomes LOWER than the sensory block

49
Q

state the order of the 3 blocks that occur following a SA spinal injection

A

Sympathetic
Sensory
Motor

50
Q

Metabolism of LA:

Ester LA are metabolized how?

A

plasma pseudocholinesterases

51
Q

Metabolism of LA:

Amides are metabolized how?

A 
the liver (CYP450)
(think AMiDE and LiVER)
52
Q

Toxicity of LA:

what 2 LA can cause methemoglobin?

A

Benzocaine

Prilocaine

53
Q

Toxicity of LA:

Methemoglobin is Ferric what?

A

Ferric 3 (Fe3)

54
Q 
Toxicity of LA:
is Fe2 (ferrous) good or bad?
55
Q 
Toxicity of LA:
is Fe3 (ferric) good or bad
A

bad causes methemoglobin

56
Q

Toxicity of LA:

if you have methemoglobin (Fe3) what drug do you give to treat it

A

Methylene blue 1-2 mg/kg IV

Converts Fe3 back to Fe2

57
Q

what is the ONE ester that is metabolized via the liver?

58
Q

Toxicity of LA: MAX DOSES

Lidocaine and Mepivacaine plain and w/ epi

A

Plain 4.5 mg/Kg or 300mg
W/ epi 7 mg/Kg or 500mg
think of 2, 4.5 + 2 is almost 7 then 300 + 2oo =500

59
Q

Toxicity of LA: MAX DOSES

Bupivacaine and Ropivaceine plain and w/epi

A

Plain 2.8 mg/Kg or 175 mg
w/ epi 3.2 mg/kg or 225 mg
just think 3 its in the middle of both

60
Q

Toxicity of LA: MAX DOSES

max of procaine and chloroprocaine

61
Q

Toxicity of LA: MAX DOSES

Cocaine and tetracaine

62
Q

Toxicity of LA: MAX DOSES

max of benzocaine spray

63
Q

Toxicity of LA:

what is the drug for treatment

A 
lipid emulsion (20% intralipid) 1.5 mL/kg
followed by infusion of 0.25 mL/kg/min
64
Q

Toxicity of LA:

name how to treat

A 
Airway 
Breathing
Circulation
Intralipids
Benzo (for seizures)
65
Q

Toxicity of LA:

what drugs do you want to avoid if toxicity occurs

A

Vasopressin
CCB
BB
LA

66
Q

Manifestation of Toxicity of LA:

what is the therapeutic plasma level of lidocaine?

67
Q

Manifestation of Toxicity of LA: LIDOCAINE
Name SE (SE progress in this order for ALL LA)
1-5 mcg/mL (x1)

A

analgesia

therapeutic

68
Q

Manifestation of Toxicity of LA: LIDOCAINE
Name SE (SE progress in this order for ALL LA)
5-10mcg/mL (x2)

A 
Lightheaded
tinnitus
visual disturbance
Numbness of tongue
Muscle twitching
69
Q

Manifestation of Toxicity of LA: LIDOCAINE
Name SE (SE progress in this order for ALL LA)
10-15 mcg/mL (x3)

A

Seizures

CONVULSIONS

70
Q

Manifestation of Toxicity of LA: LIDOCAINE
Name SE (SE progress in this order for ALL LA)
14-25 mcg/mL (x4)

A

unconsciousness
COMA
respiratory arrest

71
Q

Manifestation of Toxicity of LA: LIDOCAINE
Name SE (SE progress in this order for ALL LA)
> 25 mcg/mL (x5)

A

CARDIOVASCULAR depression

72
Q

Manifestation of Toxicity of LA:

state the order on which toxic manifestations occur

A

Light headed/ tinnitus/ numbness tongue
Convulsions (SZ)
Coma
CV collapse

73
Q

Manifestation of Toxicity of LA:

what is the plasma concentration of Lidocaine at which early S/S of toxicity are elicited

A

5-10mcg/mL

2 Xs the therapeutic dose

74
Q

Miscellaneous facts and Issues:

how do u tell amides from esters

A

amides have 2 i’s (bupIvacaIne, ropIvacaIne, prIlocaIne)

esters only have 1 i (cacaIne, tetracaIne, procaine)

75
Q

Miscellaneous facts and Issues:

what is the LA that all others are compared to?

76
Q

Miscellaneous facts and Issues:

the actions of Ester LA would be prolonged in a pt with what disorder

A

atypical pseudocholinesterase

77
Q 
Miscellaneous facts and Issues:
chronic therapy with what drug class prolongs the action of Ester LA bc they depress pseudocholinesterase function
A

Acetlycholinesterase inhibitors (edrophonium, neostigmine)

78
Q 
Miscellaneous facts and Issues:
which class ester or amide is higher risk for allergic reaction
79
Q

Miscellaneous facts and Issues:

what is the metabolic end-product of ester metabolism (also the cause of why there is an increased in allergic reaction)

A

Para-aminobenzoic acid (PABA)

80
Q

Miscellaneous facts and Issues:

what LA differs from all other LA in that it is a vasoconstrictor and it is naturally-occurring?

81
Q 
Miscellaneous facts and Issues:
what class of LA doesn't accumulate in the blood? why?
A

Ester LA

bc they are metabolized be pseudocholinesterase (plasma cholinesterase, butyrocholinesterase)

82
Q

Miscellaneous facts and Issues:
what LA is suitable for OB bc it is rapidly metabolize by plasma cholinesterases, thus the plasma level will normally be kept low. it is important b/c LA cross the placental barrier.

A

Chloroprocaine

83
Q

Miscellaneous facts and Issues:

what depresses the activity of pseudocholinesterase?

84
Q

Miscellaneous facts and Issues:

if pseudocholinesterase is normal dibucaine will depress the activity of pseudocholinesterase by how much?

85
Q

Miscellaneous facts and Issues:

the % that dibucaine depressed pseudocholinesterase is called what?

A

dibucaine #

86
Q

Miscellaneous facts and Issues:

what is normal dibucaine # and what does it mean?

A

80 = 80% (75-85)

it means that it causes 80% depression

87
Q

Miscellaneous facts and Issues:

if the dibucaine # is 20, what disorder is the pt said to have

A

homozygote atypical pseudocholinesterase

88
Q

Miscellaneous facts and Issues:

if the dibucaine # is b/t 30-70 the pt is said to have what

A

heterozygote atypical pseudocholinesterase

89
Q

Miscellaneous facts and Issues:

what is the major problem with atypical pseudocholinesterase

A

incapable of hydrolyzing SCh

(the lower the Dibucaine # the slower hydrolysis of SCh an date longer duration of SCh

90
Q

Miscellaneous facts and Issues:

the likely cause of bradycardia after SA injection is what?

A

blockade of cardiac sympathetic preganglionic fibers. (T1-T4)

91
Q

Miscellaneous facts and Issues:

if a pt becomes nauseous 5 min after spinal what likely is the cause

A

Hypotension

92
Q

Miscellaneous facts and Issues:

the dose of LA administered Epidurally is reduced what % in the parturient?

93
Q

Miscellaneous facts and Issues:

what is responsible for the hypotension associated with spinal and epidural anesthesia

A

blockage of sympathetic preganglionic nerves

► Med Misc 44 (72 decks)

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