Local anesthetics 5

Question 1

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

Answer 1

a. benzocaine
b. cetacaine
d. EMLA cream

Question 2

Methemoglobin is formed when

Answer 2

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

Question 3

Methemoglobinemia reduces

Answer 3

oxygen carrying capacity

Question 4

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

Answer 4

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

Question 5

What are drugs that produce methemoglobin?

Answer 5

benzocaine
cetacaine
prilocaine
EMLA cream
phenytoin
nitroprusside
nitroglycerine

Question 6

Signs and symptoms of methemoglobinemia include

Answer 6

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

Question 7

A significant concentration of methemoglobin can lead to an erroneous

Answer 7

SpO2 reading of 85%

Question 8

A ____________ is required to diagnose methemoglobinemia.

Answer 8

co-oximeter

Question 9

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

Answer 9

Cyanosis

Question 10

What is the treatment for methemoglobinemia?

Answer 10

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

Question 11

Patients with ______________ should not receive methylene blue because _____________

Answer 11

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

Question 12

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

Answer 12

an exchange transfusion

Question 13

_____________ are at higher risk for toxicity with methemoglobinemia.

Answer 13

Neonates

Question 14

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

Answer 14

2 g

Question 15

5% EMLA cream is a mixture of

Answer 15

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

Question 16

EMLA produces analgesia within ___________ and achieves maximum effect after _______

Answer 16

one hour; after 2-3 hours

Question 17

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

Answer 17

Skin conditions such as eczema, psoriasis, and skin wounds

Question 18

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

Answer 18

o-toluidine

Question 19

_________________ are more likely to become toxic with EMLA cream.

Answer 19

infants & small children

Question 20

Uses for EMLA cream include

Answer 20

arterial or venous cannulation, lumbar puncture or myringotomy

Question 21

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

Answer 21

Nitroglycerin

Question 22

Dose recommendations of EMLA cream for <5 kg

Answer 22

1 g

Question 23

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

Answer 23

2 g

Question 24

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

Answer 24

10 g

Question 25

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

Answer 25

20 g

Question 26

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

Answer 26

d. hyaluronidase

Question 27

Drugs that prolong local anesthetic duration of action include

Answer 27

epinephrine dexamethasone dextran

Question 28

Drugs that provide supplemental analgesia include

Answer 28

epinephrine clonidine opioids

Question 29

Drugs that shorten onset time of LAs include

Answer 29

sodium bicarbonate (the clinical relevance of this is debatable)

Question 30

________ improves local anesthetic diffusion through tissues.

Answer 30

Hyaluronidase

Question 31

Hyaluronidase hydrolyzes hyaluronic acid which facilitates

Answer 31

diffusion of substances in the tissues

Question 32

Hyaluronidase is commonly used in

Answer 32

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

Question 33

What is beneficial about hyaluronidase for ophthalmic blocks?

Answer 33

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

Question 34

A downside of hyaluronidase is that it has

Answer 34

an allergic potential

Question 35

Describe the dosing of sodium bicarbonate as a mixture with LA

Answer 35

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

Question 36

Benefits of sodium bicarbonate include

Answer 36

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

Question 37

The MOA of clonidine is

Answer 37

alpha 2 receptor agonism produces analgesia

Question 38

The dose of clonidine for LAs is

Answer 38

100 mcg

Question 39

The MOA of epinephrine is

Answer 39

alpha-2 agonism

Question 40

Opioids provide supplemental analgesia for _____________

Answer 40

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

Question 41

______________ reduces the effectiveness of opioids in the epidural space

Answer 41

Chloroprocaine

Question 42

Low doses of local anesthetic produce

Answer 42

vasoconstriction

Question 43

High doses of local anesthetic produce

Answer 43

vasodilation

Question 44

Epinephrine is a potent

Answer 44

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

Question 45

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

Answer 45

intermediate duration compared to those of long duration

Question 46

Low molecular weight dextran

Answer 46

prolongs block duration by decreasing systemic uptake of LAs

Question 47

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

Answer 47

50%

Question 48

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

Answer 48

glucocorticoid activity

Question 49

_____________ does not possess intrinsic vasodilating properties

Answer 49

Cocaine