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Apex Review > Local anesthetics 5 > Flashcards

Local anesthetics 5 Flashcards

1
Q

Which local anesthetics are MOST likely to produce methemoglobinemia? (select 3)
a. benzocaine
b. cetacaine
c. mepivacaine
d. EMLA cream
e. ropivacaine
f. etidocaine

A

a. benzocaine
b. cetacaine
d. EMLA cream

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2
Q

Methemoglobin is formed when

A

the iron molecule on hemoglobin (Fe+2) is oxidized to its ferric form (Fe3+)

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3
Q

Methemoglobinemia reduces

A

oxygen carrying capacity

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4
Q

What are the two ways in which methemoglobinemia reduces oxygen carrying capacity?

A
  1. methemoglobin can’t bind oxygen molecules
  2. methemoglobin shifts the oxyhemoglobin dissociation curve to the left
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5
Q

What are drugs that produce methemoglobin?

A

benzocaine
cetacaine
prilocaine
EMLA cream
phenytoin
nitroprusside
nitroglycerine

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6
Q

Signs and symptoms of methemoglobinemia include

A

hypoxia that isn’t fixed by increasing the FiO2
cyanosis
chocolate colored blood
tachycardia
tachypnea
changes in LOC

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7
Q

A significant concentration of methemoglobin can lead to an erroneous

A

SpO2 reading of 85%

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8
Q

A ____________ is required to diagnose methemoglobinemia.

A

co-oximeter

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9
Q

____________ in the presence of normal or high PaO2 is suggestive of methemoglobinemia.

A

Cyanosis

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10
Q

What is the treatment for methemoglobinemia?

A

methylene blue at a dose of 1-2 mg/kg over 5 minutes
(max dose= 7-8 mg/kg)

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11
Q

Patients with ______________ should not receive methylene blue because _____________

A

glucose-6 phosphate reductase deficiency because they do not possess methemoglobin reductase

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12
Q

Patients with glucose-6-phosphate reductase deficiency may require ___________ if they have methemoglobinemia.

A

an exchange transfusion

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13
Q

_____________ are at higher risk for toxicity with methemoglobinemia.

A

Neonates

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14
Q

What is the MAXIMUM dose of EMLA cream for a 9 month old infant who weights 8 kg?

A

2 g

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15
Q

5% EMLA cream is a mixture of

A

50/50 combination of 2.5% lidocaine & 2.5% prilocaine

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16
Q

EMLA produces analgesia within ___________ and achieves maximum effect after _______

A

one hour; after 2-3 hours

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17
Q

______________________ can alter EMLA pharmacokinetics and may increase the risk of toxicity.

A

Skin conditions such as eczema, psoriasis, and skin wounds

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18
Q

Prilocaine is metabolized to ____________________, which oxidizes hemoglobin to methemoglobin.

A

o-toluidine

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19
Q

_________________ are more likely to become toxic with EMLA cream.

A

infants & small children

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20
Q

Uses for EMLA cream include

A

arterial or venous cannulation, lumbar puncture or myringotomy

21
Q

___________ can be applied simultaneously to hasten the absorption of EMLA.

A

Nitroglycerin

22
Q

Dose recommendations of EMLA cream for <5 kg

A

1 g

23
Q

Maximum dose of EMLA cream for 3-12 months and >5 kg

A

2 g

24
Q

Maximum dose of EMLA cream for 1-6 years and >10 kg

A

10 g

25
Q

Maximum dose of EMLA cream for 7-12 years and >20 kg

A

20 g

26
Q

Each additive prolongs the duration of local anesthetics EXCEPT:
a. dexamethasone
b. dextran
c. epinephrine
d. hyaluronidase

A

d. hyaluronidase

27
Q

Drugs that prolong local anesthetic duration of action include

A

epinephrine
dexamethasone
dextran

28
Q

Drugs that provide supplemental analgesia include

A

epinephrine
clonidine
opioids

29
Q

Drugs that shorten onset time of LAs include

A

sodium bicarbonate (the clinical relevance of this is debatable)

30
Q

________ improves local anesthetic diffusion through tissues.

A

Hyaluronidase

31
Q

Hyaluronidase hydrolyzes hyaluronic acid which facilitates

A

diffusion of substances in the tissues

32
Q

Hyaluronidase is commonly used in

A

ophthalmic blocks to increase the speed of onset, enhance block quality, and mitigate a rise in intraocular pressure

33
Q

What is beneficial about hyaluronidase for ophthalmic blocks?

A

it reduces hematoma size as well as decreases the risk of postoperative strabismus

34
Q

A downside of hyaluronidase is that it has

A

an allergic potential

35
Q

Describe the dosing of sodium bicarbonate as a mixture with LA

A

1 mL of 8.4% of sodium bicarbonate with 10 mL of LA solution

36
Q

Benefits of sodium bicarbonate include

A

speeds up onset of action because alkalization increases the number of lipid-soluble molecules
increases the quality of the block
reduces pain on injection

37
Q

The MOA of clonidine is

A

alpha 2 receptor agonism produces analgesia

38
Q

The dose of clonidine for LAs is

A

100 mcg

39
Q

The MOA of epinephrine is

A

alpha-2 agonism

40
Q

Opioids provide supplemental analgesia for _____________

A

spinal & epidural anesthesia; when used in peripheral blocks, the results have been mixed

41
Q

______________ reduces the effectiveness of opioids in the epidural space

A

Chloroprocaine

42
Q

Low doses of local anesthetic produce

A

vasoconstriction

43
Q

High doses of local anesthetic produce

A

vasodilation

44
Q

Epinephrine is a potent

A

vasoconstrictor that can decrease systemic uptake of local anesthetic, prolong block duration, and enhance block quality

45
Q

Epinephrine does a better job of prolonging local anesthetics of ________ duration compared to those of _________ duration.

A

intermediate duration compared to those of long duration

46
Q

Low molecular weight dextran

A

prolongs block duration by decreasing systemic uptake of LAs

47
Q

Dexamethasone can increase the duration of brachial plexus blockade by up to

A

50%

48
Q

The ability of dexamethasone to extend local anesthetic duration of action correlates with

A

glucocorticoid activity

49
Q

_____________ does not possess intrinsic vasodilating properties

A

Cocaine

Apex Review (224 decks)

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