Local Anesthetics Flashcards
Where do local anesthetics bind to the sodium channel?
the alpha subunit on the inside of the sodium channel when it’s in its active or inactive state
Do local anesthetics affect RMP or TP?
No, neither. They only prevent the nerve from repolarizing.
What characteristic is onset of action of a LA most related to?
pKa
What characteristic is potency of a LA most related to?
Lipid solubility
What is the max dose of levobupivacaine?
2 mg/kg
150 mg
What is the max dose of bupivacaine?
2.5 mg/kg
175 mg
What is the max dose of bupivacaine w/ epi?
3 mg/kg
200 mg
What is the max dose of ropivacaine?
3 mg/kg
200 mg
What is the max dose of lidocaine?
4.5 mg/kg
300 mg
What is the max dose of mepivacaine?
7 mg/kg
400 mg
What is the max dose of lidocaine w/ epi?
7 mg/kg
500 mg
What is the max dose of prilocaine?
8 mg/kg
<70 kg = 500 mg
>70 kg = 600 mg
What is the max dose of procaine?
7 mg/kg
350-600 mg
What is the max dose of chloroprocaine?
11 mg/kg
800 mg
What is the max dose of chloroprocaine w/ epi?
14 mg/kg
1,000 mg
What characteristic is duration of action of a LA most related to?
Protein binding
What SS appear when the plasma concentration of lidocaine is 1-5 mcg/mL?
analgesia
What SS appear when the plasma concentration of lidocaine is 5-10 mcg/mL?
numbness of lips and tongue
tinnitus
restlessness
vertigo
skeletal muscle twitching
blurred vision
hypotension
myocardial depression
What SS appear when the plasma concentration of lidocaine is 10-15 mcg/mL?
seizures
loss of consciousness
What SS appear when the plasma concentration of lidocaine is 15-25 mcg/mL?
coma
respiratory arrest
What SS appear when the plasma concentration of lidocaine is >25 mcg/mL?
cardiovascular collapse
What is the dose of lipid emulsion therapy in LAST in a patient > 70kg?
bolus: 100 mL over 2-3 min
infusion: 250 mL over 15-20 min
if needed, repeat bolus and/or double infusion
What is the dose of lipid emulsion therapy in LAST in a patient < 70kg?
bolus: 1.5 mg/kg LBW over 2-3 min
infusion: 0.25 mL/kg/min
if needed, repeat bolus or double infusion rate
What is the proposed mechanism of action of lipid emulsion therapy in LAST?
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
Discuss ACLS in LAST:
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
How can EMLA cream on an infant lead to methemoglobinemia?
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.
What is the maximum dose and area of application of EMLA cream in a 0-3 month or <5 kg neonate?
1 g
10 cm2
What is the maximum dose and area of application of EMLA cream in a 3-12 month or >5 kg neonate?
2 g
20 cm2
What is the maximum dose and area of application of EMLA cream in a 1-6 year old or >10 kg child?
10 g
100 cm2
What is the maximum dose and area of application of EMLA cream in a 7-12 year old or >20 kg child?
20 g
200 cm2
What skin conditions preclude EMLA cream?
Don’t use EMLA cream on psoriasis, eczema, or skin wounds. Increased risk of toxicity would result.
What drug can be added to EMLA cream to hasten its onset?
nitroglycerine
What drugs prolong the duration of action of local anesthetics and how?
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
What drugs promote analgesia when added to local anesthetics and how?
Clonidine: alpha 2 agonism (100 mcg)
Epinephrine: alpha 2 agonism
Opioids: not with chloroprocaine (reduces effectiveness of opioids in epidural space)
What can be added to shorten onset time of local anesthetics?
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
What drug improves diffusion of local anesthetics through tissues?
Hyaluronidase: hyaluronic acid hinders LA spread through tissues, and hyaluronidase hydrolyzes it, allowing diffusion into tissues.
It has an allergic potential.
