Local anesthetics 5 Flashcards
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. benzocaine
b. cetacaine
d. EMLA cream
Methemoglobin is formed when
the iron molecule on hemoglobin (Fe+2) is oxidized to its ferric form (Fe3+)
Methemoglobinemia reduces
oxygen carrying capacity
What are the two ways in which methemoglobinemia reduces oxygen carrying capacity?
- methemoglobin can’t bind oxygen molecules
- methemoglobin shifts the oxyhemoglobin dissociation curve to the left
What are drugs that produce methemoglobin?
benzocaine
cetacaine
prilocaine
EMLA cream
phenytoin
nitroprusside
nitroglycerine
Signs and symptoms of methemoglobinemia include
hypoxia that isn’t fixed by increasing the FiO2
cyanosis
chocolate colored blood
tachycardia
tachypnea
changes in LOC
A significant concentration of methemoglobin can lead to an erroneous
SpO2 reading of 85%
A ____________ is required to diagnose methemoglobinemia.
co-oximeter
____________ in the presence of normal or high PaO2 is suggestive of methemoglobinemia.
Cyanosis
What is the treatment for methemoglobinemia?
methylene blue at a dose of 1-2 mg/kg over 5 minutes
(max dose= 7-8 mg/kg)
Patients with ______________ should not receive methylene blue because _____________
glucose-6 phosphate reductase deficiency because they do not possess methemoglobin reductase
Patients with glucose-6-phosphate reductase deficiency may require ___________ if they have methemoglobinemia.
an exchange transfusion
_____________ are at higher risk for toxicity with methemoglobinemia.
Neonates
What is the MAXIMUM dose of EMLA cream for a 9 month old infant who weights 8 kg?
2 g
5% EMLA cream is a mixture of
50/50 combination of 2.5% lidocaine & 2.5% prilocaine
EMLA produces analgesia within ___________ and achieves maximum effect after _______
one hour; after 2-3 hours
______________________ can alter EMLA pharmacokinetics and may increase the risk of toxicity.
Skin conditions such as eczema, psoriasis, and skin wounds
Prilocaine is metabolized to ____________________, which oxidizes hemoglobin to methemoglobin.
o-toluidine
_________________ are more likely to become toxic with EMLA cream.
infants & small children
Uses for EMLA cream include
arterial or venous cannulation, lumbar puncture or myringotomy
___________ can be applied simultaneously to hasten the absorption of EMLA.
Nitroglycerin
Dose recommendations of EMLA cream for <5 kg
1 g
Maximum dose of EMLA cream for 3-12 months and >5 kg
2 g
Maximum dose of EMLA cream for 1-6 years and >10 kg
10 g
Maximum dose of EMLA cream for 7-12 years and >20 kg
20 g
Each additive prolongs the duration of local anesthetics EXCEPT:
a. dexamethasone
b. dextran
c. epinephrine
d. hyaluronidase
d. hyaluronidase
Drugs that prolong local anesthetic duration of action include
epinephrine
dexamethasone
dextran
Drugs that provide supplemental analgesia include
epinephrine
clonidine
opioids
Drugs that shorten onset time of LAs include
sodium bicarbonate (the clinical relevance of this is debatable)
________ improves local anesthetic diffusion through tissues.
Hyaluronidase
Hyaluronidase hydrolyzes hyaluronic acid which facilitates
diffusion of substances in the tissues
Hyaluronidase is commonly used in
ophthalmic blocks to increase the speed of onset, enhance block quality, and mitigate a rise in intraocular pressure
What is beneficial about hyaluronidase for ophthalmic blocks?
it reduces hematoma size as well as decreases the risk of postoperative strabismus
A downside of hyaluronidase is that it has
an allergic potential
Describe the dosing of sodium bicarbonate as a mixture with LA
1 mL of 8.4% of sodium bicarbonate with 10 mL of LA solution
Benefits of sodium bicarbonate include
speeds up onset of action because alkalization increases the number of lipid-soluble molecules
increases the quality of the block
reduces pain on injection
The MOA of clonidine is
alpha 2 receptor agonism produces analgesia
The dose of clonidine for LAs is
100 mcg
The MOA of epinephrine is
alpha-2 agonism
Opioids provide supplemental analgesia for _____________
spinal & epidural anesthesia; when used in peripheral blocks, the results have been mixed
______________ reduces the effectiveness of opioids in the epidural space
Chloroprocaine
Low doses of local anesthetic produce
vasoconstriction
High doses of local anesthetic produce
vasodilation
Epinephrine is a potent
vasoconstrictor that can decrease systemic uptake of local anesthetic, prolong block duration, and enhance block quality
Epinephrine does a better job of prolonging local anesthetics of ________ duration compared to those of _________ duration.
intermediate duration compared to those of long duration
Low molecular weight dextran
prolongs block duration by decreasing systemic uptake of LAs
Dexamethasone can increase the duration of brachial plexus blockade by up to
50%
The ability of dexamethasone to extend local anesthetic duration of action correlates with
glucocorticoid activity
_____________ does not possess intrinsic vasodilating properties
Cocaine
