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Apex > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

In what order are perceptions lost with local anesthetics

A
  1. Pain
  2. Cold
  3. Warmth
  4. Touch
  5. Deep Pressure
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2
Q

The ability of an anesthetic to penetrate the axon membrane is determined by three properties:

A

Molecular size

Lipid solubility

degree of ionization at tissue pH

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3
Q

Where are esters metabolized?

A

in the blood by esterases

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4
Q

Where are amides metabolized?

A

In the liver

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5
Q

When absorbed in sufficient quantities, local anesthetics cause CNS ______ followed by ________

A

excitation followed by depression

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6
Q

In large quantities, how do systemic local anesthetics effect the heart?

A

Risk for decreased conduction: bradycardia, heart block, reduced EF

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7
Q

What effect do local anesthetics have on blood vessels?

A

Vasodilation

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8
Q

Which local anesthetic can cause methemoglobinemia?

A

Topical benzocaine (usually in children < 2 years)

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9
Q

Allergic reactions are much more common in response to ____ anesthetics than _____

A

more common in ester than amide

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10
Q

If a patient is allergic to Lidocaine, how likely is it that they are allergic to Tetracaine?

A

Very low. Cross-hypersensitivity between amides and esters is very low

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11
Q

If a patient is allergic to Lidocaine, how likely is it that they are allergic to Mepivicaine?

A

VERY VERY likely

If you’re allergic to one local anesthetic in a class, you’re allergic to all the others in that class

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12
Q

List the Amide LAs:

A

Lidocaine

Bupivicaine

Mepivicaine

Prilocaine

Ropivicaine

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13
Q

List the Ester LAs

A

Procaine

Chloroprocaine

Tetracaine

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14
Q

What was the first local anesthetic?

A

Cocaine (ester type)

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15
Q

Is procaine more effective topically or by injection?

A

Injection only. Not effective topically

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16
Q

What are five tips for avoiding LAST?

A
  1. Apply the smallest amount needed
  2. Avoid application to large areas
  3. Don’t put on broken or irritated skin
  4. Avoid strenuous exercise
  5. Avoid wrapping or anything that increases skin temperature
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17
Q

Conduction velocity is increased by:

A

myelination and diameter

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18
Q

What is the function of A alpha nerves?

A

Skeletal muscle MOTOR
AND
Proprioception

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19
Q

What is the function of A beta nerves?

A

Touch and Pressure

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20
Q

What is the function of A gamma nerves?

A

Skeletal muscle TONE

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21
Q

What is the function of A delta nerves?

A

Fast pain
AND
Temperature
AND
Touch

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22
Q

What is the function of B nerves?

A

PRE ganglionic ANS fibers

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23
Q

What is the function of C fibers?

A

POST ganglionic ANS
AND
Slow Pain/Temp/Touch

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24
Q

Which nerve fibers are heavily myelinated?

A

A alpha and beta

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25
Q

Which nerve fibers have medium myelination?

A

A gamma and delta

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26
Q

Which nerve fibers have light myelination?

A

B Fibers

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27
Q

Which nerve fibers have no myelination?

A

C Fibers

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28
Q

What is Cm?

A

The minimum effective concentration of a local anesthetic, the ED95 of LAs

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29
Q

In the clinical setting, LAs inhibit nerves in the following order:

A

B
C
A (g+d)
A (a+b)

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30
Q

What is the resting membrane potential in a peripheral nerve?

A

-70 mV

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31
Q

What is the threshold potential of a peripheral nerve?

A

-55 mV

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32
Q

What is the primary determinant of resting membrane potential?

A

Serum K

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33
Q

An increase in serum K ______ the RMP

A

decreases the RMP (makes it more positive)

34
Q

A decrease in serum K ______ the RMP

A

increases the RMP (makes it more negative)

35
Q

What is the primary determinant of threshold potential?

A

Serum Ca

36
Q

An increase in serum Ca ______ the threshold potential

A

makes the threshold potential more positive

37
Q

A decrease in serum Ca ______ the threshold potential

A

makes the threshold potential more negative

38
Q

Where do local anesthetics bind?

A

On the INSIDE of the alpha subunit of sodium channels

39
Q

When local anesthetics are placed in solution, they dissociate into:

A

an uncharged base and a conjugate acid

40
Q

When local anesthetics are placed in the plasma, what happens?

A

Since all LAs are stored in acidic environments, they enter the plasma as conjugate acids (LA+).

In plasma, about 50% of it dissociates into an uncharged base (LA minus its hydrogen atom). This makes it lipid soluble.

41
Q

How are bases stored in the vial?

A

Remember, polarized atoms are dissolvable in water. You want the weak base to be in an acidic environment to keep it water soluble. All LAs are stored in acidic environments

42
Q

Once an uncharged base travels through the axolemma, what happens?

A

ICF is actually MORE acidic than ECF. So even though the uncharged base didn’t ionize in the ECF, it does when it hits the ICF. It adopts a hydrogen atom, becoming LA+, which makes it able to bind to the alpha subunit

43
Q

Local anesthetic molecules have three components:

A
44
Q

Which portion of a LA is liphophilic?

A

The aromatic ring

45
Q

Which portion of the LA is hydrophilic?

A

The tertiary amine

46
Q

The intermediate chain of a LA determines:

A

Drug Class
Metabolism
Allergic Potential

47
Q

Onset of action is determined by:

A

pKA

48
Q

Duration of action is determined by:

A

protein binding

49
Q

Potency is determined by:

A

Lipid solubility

50
Q

What is the pKa of Bupivacaine and Ropivacaine?

A

8.1

51
Q

What LA has the highest degree of protein binding?

A

Bupivacaine at 96%

Follow by Ropivacaine at 94%

52
Q

Which LA has the highest pKa?

A

Procaine at 8.9, followed closely by chloroprocaine and tetracaine

All of the esters have higher pKa than the amides

53
Q

Which LA does not undergo protein binding?

A

Chloroprocaine

54
Q

There is only one LA with a pKa well below 7. Which one is it?

A

Benzocaine, with a pKa of 3.5!

55
Q

Which sites have the highest uptake of LA?

A
56
Q

The effect of added epinephrine is greatest with which LAs?

A

The ones that have the highest degree of intrinsic vasodilating activity, such as Lidocaine

57
Q

If a patient receives exparel, what are the rules for subsequent lidocaine administration?

A

If they get exparel, they can’t have any other lidocaine for at least 96 hours

58
Q

If the surgeon uses lidocaine infiltration intraoperatively, how long until exparel can be administered?

A

At least 20 minutes

59
Q

LAs preferentially bind to which serum protein?

A

Alpha-1-acid Glycoprotein

60
Q

What is the maximum dose of exparel?

A

2 vials

61
Q

What is the maximum allowable dose of lidocaine?

A

4.5 mg/kg, never more than 300mg

62
Q

What is the maximum allowable dose of Bupivacaine?

A

2.5 mg/kg, never more than 175 mg

63
Q

What is the maximum allowable dose of Ropivacaine?

A

3 mg/kg, never more than 200 mg

64
Q

Risk of LAST is increased by:

A

Hypoxia
Hypercarbia
Acidosis
HYPERkalemia

65
Q

What is the initial intralipid bolus dose?

A

1.5ml/kg

66
Q

If a patient in LAST is having dysrhythmias, what is the drug of choice?

A

Amiodarone

DO NOT use calcium channel blockers or beta blockers

67
Q

Which drugs should be avoided in LAST resuscitations?

A

Vasopressin
AND
Epi (decreases effectiveness of intralipid)

68
Q

If a patient is over 70kg, what should their initial bolus of intralipid be?

A

Just start with 100ml and move on to a drip of 250ml over 15-20 minutes

69
Q

What is the maximum dose of intralipid therapy?

A

12mg/kg

70
Q

What is the maximum recommended dose of lidocaine in tumescent solutions?

A

55 mg/kg

71
Q

Which anesthetics are most likely to produce methemeglobinemia?

A

EMLA
Benzocaine
Cetacaine

72
Q

What is methemeglobinemia?

A

When the Fe2+ on hemoglobin is oxidized to Fe3+, which does not allow hemoglobin to bind oxygen

73
Q

What are the s/s of methemoglobinemia?

A

Chocolate blood!
Cyanosis
Refractory hypoxia
Tachycardia
Tachypnea
Altered LOC

74
Q

What is the treatment for methemoglobinemia?

A

1-2 mg/kg methylene blue of 2-5 minutes

75
Q

Methemoglobinemia causes the p50 to shift:

A

To the left

76
Q

What drugs besides LAs can cause methemoglobinemia?

A

Nipride and Nitroglycerine

77
Q

EMLA cream is a combination of:

A

2.5% Lidocaine
2.5% Prilocaine

78
Q

Drugs that prolong the duration of LAs include:

A

Epinephrine
Decadron
Dextran

79
Q

Drugs that provide supplemental analgesia with LAs include:

A

Epinephrine
Clonidine
Opioids

80
Q

How much bicarb can be added to LA?

A

You can add 1ml of 8.4% bicarb for every 10ml of LA

81
Q

What is the effect of adding hyaluronidase to LA?

A

Improves LA diffusion through tissues

82
Q

As pKa approaches 7.4, does the speed of onset increase or decrease?

A

It increases, because a larger fraction of the solution will exist as lipid soluble, uncharged solution

Apex (46 decks)

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