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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
Which nerve fibers have medium myelination?
A gamma and delta
26
Which nerve fibers have light myelination?
B Fibers
27
Which nerve fibers have no myelination?
C Fibers
28
What is Cm?
The minimum effective concentration of a local anesthetic, the ED95 of LAs
29
In the clinical setting, LAs inhibit nerves in the following order:
B C A (g+d) A (a+b)
30
What is the resting membrane potential in a peripheral nerve?
-70 mV
31
What is the threshold potential of a peripheral nerve?
-55 mV
32
What is the primary determinant of resting membrane potential?
Serum K
33
An increase in serum K ______ the RMP
decreases the RMP (makes it more positive)
34
A decrease in serum K ______ the RMP
increases the RMP (makes it more negative)
35
What is the primary determinant of threshold potential?
Serum Ca
36
An increase in serum Ca ______ the threshold potential
makes the threshold potential more positive
37
A decrease in serum Ca ______ the threshold potential
makes the threshold potential more negative
38
Where do local anesthetics bind?
On the INSIDE of the alpha subunit of sodium channels
39
When local anesthetics are placed in solution, they dissociate into:
an uncharged base and a conjugate acid
40
When local anesthetics are placed in the plasma, what happens?
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
How are bases stored in the vial?
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
Once an uncharged base travels through the axolemma, what happens?
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
Local anesthetic molecules have three components:
44
Which portion of a LA is liphophilic?
The aromatic ring
45
Which portion of the LA is hydrophilic?
The tertiary amine
46
The intermediate chain of a LA determines:
Drug Class Metabolism Allergic Potential
47
Onset of action is determined by:
pKA
48
Duration of action is determined by:
protein binding
49
Potency is determined by:
Lipid solubility
50
What is the pKa of Bupivacaine and Ropivacaine?
8.1
51
What LA has the highest degree of protein binding?
Bupivacaine at 96% Follow by Ropivacaine at 94%
52
Which LA has the highest pKa?
Procaine at 8.9, followed closely by chloroprocaine and tetracaine All of the esters have higher pKa than the amides
53
Which LA does not undergo protein binding?
Chloroprocaine
54
There is only one LA with a pKa well below 7. Which one is it?
Benzocaine, with a pKa of 3.5!
55
Which sites have the highest uptake of LA?
56
The effect of added epinephrine is greatest with which LAs?
The ones that have the highest degree of intrinsic vasodilating activity, such as Lidocaine
57
If a patient receives exparel, what are the rules for subsequent lidocaine administration?
If they get exparel, they can't have any other lidocaine for at least 96 hours
58
If the surgeon uses lidocaine infiltration intraoperatively, how long until exparel can be administered?
At least 20 minutes
59
LAs preferentially bind to which serum protein?
Alpha-1-acid Glycoprotein
60
What is the maximum dose of exparel?
2 vials
61
What is the maximum allowable dose of lidocaine?
4.5 mg/kg, never more than 300mg
62
What is the maximum allowable dose of Bupivacaine?
2.5 mg/kg, never more than 175 mg
63
What is the maximum allowable dose of Ropivacaine?
3 mg/kg, never more than 200 mg
64
Risk of LAST is increased by:
Hypoxia Hypercarbia Acidosis HYPERkalemia
65
What is the initial intralipid bolus dose?
1.5ml/kg
66
If a patient in LAST is having dysrhythmias, what is the drug of choice?
Amiodarone DO NOT use calcium channel blockers or beta blockers
67
Which drugs should be avoided in LAST resuscitations?
Vasopressin AND Epi (decreases effectiveness of intralipid)
68
If a patient is over 70kg, what should their initial bolus of intralipid be?
Just start with 100ml and move on to a drip of 250ml over 15-20 minutes
69
What is the maximum dose of intralipid therapy?
12mg/kg
70
What is the maximum recommended dose of lidocaine in tumescent solutions?
55 mg/kg
71
Which anesthetics are most likely to produce methemeglobinemia?
EMLA Benzocaine Cetacaine
72
What is methemeglobinemia?
When the Fe2+ on hemoglobin is oxidized to Fe3+, which does not allow hemoglobin to bind oxygen
73
What are the s/s of methemoglobinemia?
Chocolate blood! Cyanosis Refractory hypoxia Tachycardia Tachypnea Altered LOC
74
What is the treatment for methemoglobinemia?
1-2 mg/kg methylene blue of 2-5 minutes
75
Methemoglobinemia causes the p50 to shift:
To the left
76
What drugs besides LAs can cause methemoglobinemia?
Nipride and Nitroglycerine
77
EMLA cream is a combination of:
2.5% Lidocaine 2.5% Prilocaine
78
Drugs that prolong the duration of LAs include:
Epinephrine Decadron Dextran
79
Drugs that provide supplemental analgesia with LAs include:
Epinephrine Clonidine Opioids
80
How much bicarb can be added to LA?
You can add 1ml of 8.4% bicarb for every 10ml of LA
81
What is the effect of adding hyaluronidase to LA?
Improves LA diffusion through tissues
82
As pKa approaches 7.4, does the speed of onset increase or decrease?
It increases, because a larger fraction of the solution will exist as lipid soluble, uncharged solution

Apex (46 decks)

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