Local Anesthetics

Question 1

Where do local anesthetics bind to the sodium channel?

Answer 1

the alpha subunit on the inside of the sodium channel when it’s in its active or inactive state

Question 2

Do local anesthetics affect RMP or TP?

Answer 2

No, neither. They only prevent the nerve from repolarizing.

Question 3

What characteristic is onset of action of a LA most related to?

Answer 3

pKa

Question 4

What characteristic is potency of a LA most related to?

Answer 4

Lipid solubility

Question 5

What is the max dose of levobupivacaine?

Answer 5

2 mg/kg
150 mg

Question 6

What is the max dose of bupivacaine?

Answer 6

2.5 mg/kg
175 mg

Question 7

What is the max dose of bupivacaine w/ epi?

Answer 7

3 mg/kg
200 mg

Question 8

What is the max dose of ropivacaine?

Answer 8

3 mg/kg
200 mg

Question 9

What is the max dose of lidocaine?

Answer 9

4.5 mg/kg
300 mg

Question 10

What is the max dose of mepivacaine?

Answer 10

7 mg/kg
400 mg

Question 11

What is the max dose of lidocaine w/ epi?

Answer 11

7 mg/kg
500 mg

Question 12

What is the max dose of prilocaine?

Answer 12

8 mg/kg
<70 kg = 500 mg
>70 kg = 600 mg

Question 13

What is the max dose of procaine?

Answer 13

7 mg/kg
350-600 mg

Question 14

What is the max dose of chloroprocaine?

Answer 14

11 mg/kg
800 mg

Question 15

What is the max dose of chloroprocaine w/ epi?

Answer 15

14 mg/kg
1,000 mg

Question 15

What characteristic is duration of action of a LA most related to?

Answer 15

Protein binding

Question 16

What SS appear when the plasma concentration of lidocaine is 1-5 mcg/mL?

Answer 16

analgesia

Question 17

What SS appear when the plasma concentration of lidocaine is 5-10 mcg/mL?

Answer 17

numbness of lips and tongue
tinnitus
restlessness
vertigo
skeletal muscle twitching
blurred vision

hypotension
myocardial depression

Question 18

What SS appear when the plasma concentration of lidocaine is 10-15 mcg/mL?

Answer 18

seizures
loss of consciousness

Question 19

What SS appear when the plasma concentration of lidocaine is 15-25 mcg/mL?

Answer 19

coma
respiratory arrest

Question 20

What SS appear when the plasma concentration of lidocaine is >25 mcg/mL?

Answer 20

cardiovascular collapse

Question 21

What is the dose of lipid emulsion therapy in LAST in a patient > 70kg?

Answer 21

bolus: 100 mL over 2-3 min
infusion: 250 mL over 15-20 min
if needed, repeat bolus and/or double infusion

Question 22

What is the dose of lipid emulsion therapy in LAST in a patient < 70kg?

Answer 22

bolus: 1.5 mg/kg LBW over 2-3 min
infusion: 0.25 mL/kg/min
if needed, repeat bolus or double infusion rate

Question 23

What is the proposed mechanism of action of lipid emulsion therapy in LAST?

Answer 23

Lipid sink: intravascular reservoir for LA and reduces Cp of LA
Membrane effect: impairs LA binding to voltage-gated sodium channels
Metabolic effect: enhanced myocardial fatty acid metabolism
Inotropic effect: increased Ca influx and intracellular Ca concentration

Question 24

Discuss ACLS in LAST:

Answer 24

Epi can hinder resuscitation and decrease efficacy of lipid emulsion therapy. If used, keep < 1mcg/kg.
Avoid vasopressin
Avoid lidocaine and procainamide
Amiodarone best choice for ventricular dysrhythmias

Question 25

How can EMLA cream on an infant lead to methemoglobinemia?

Answer 25

It is made of 2.5% prilocaine and 2.5% lidocaine. Prilocaine metabolizes to o-toluidine, which oxidizes hemoglobin to methemoglobin. Fetal hemoglobin is relatively deficient in methemoglobin reductase, leading to higher toxicity risk.

Question 26

What is the maximum dose and area of application of EMLA cream in a 0-3 month or <5 kg neonate?

Answer 26

1 g
10 cm2

Question 27

What is the maximum dose and area of application of EMLA cream in a 3-12 month or >5 kg neonate?

Answer 27

2 g
20 cm2

Question 28

What is the maximum dose and area of application of EMLA cream in a 1-6 year old or >10 kg child?

Answer 28

10 g
100 cm2

Question 29

What is the maximum dose and area of application of EMLA cream in a 7-12 year old or >20 kg child?

Answer 29

20 g
200 cm2

Question 30

What skin conditions preclude EMLA cream?

Answer 30

Don’t use EMLA cream on psoriasis, eczema, or skin wounds. Increased risk of toxicity would result.

Question 31

What drug can be added to EMLA cream to hasten its onset?

Answer 31

nitroglycerine

Question 32

What drugs prolong the duration of action of local anesthetics and how?

Answer 32

Epinephrine: alpha 2 agonism leads to vasoconstriction and reduced systemic uptake, prolonged block duration, and enhanced block quality
Dexamethasone: glucocortocoid activity, acts on steroid receptor and affects systemic uptake
Dextran: low molecular weight dextran decreases systemic uptake

Question 33

What drugs promote analgesia when added to local anesthetics and how?

Answer 33

Clonidine: alpha 2 agonism (100 mcg)
Epinephrine: alpha 2 agonism
Opioids: not with chloroprocaine (reduces effectiveness of opioids in epidural space)

Question 34

What can be added to shorten onset time of local anesthetics?

Answer 34

Sodium bicarbonate: alkalization leads to increased number of lipid-soluble molecules and speeds up onset of action, increases quality of block, and reduces pain on injection
Mix 1 mL of 8.4% bicarb with 10 mL of local anesthetic

Question 35

What drug improves diffusion of local anesthetics through tissues?

Answer 35

Hyaluronidase: hyaluronic acid hinders LA spread through tissues, and hyaluronidase hydrolyzes it, allowing diffusion into tissues.
It has an allergic potential.