Local Anesthetics Flashcards
What is the primary determinant of testing membrane potential?
Potassium!
Decreased serum K+ —> RMP is more negative
Increased serum K+ —> RMP is more positive
What is the primary determinant of threshold?
Calcium!
Hypocalcemia —> TP becomes more negative
Hypercalcemia —> TP becomes more positive
What determines the cell’s ability to depolarize?
The difference b/t RMP and Threshold
When RMP is closer to threshold, the cell is easier to depolarize
Are local anesthetics acids or bases?
Weak bases
What binds to the local anesthetic binding site (alpha-subunit)? Does it bing inside or outside?
Conjugate acid
Binds INSIDE the cell
When considering the molecular structure of local anesthetics, what determines lipophilicity?
Aromatic ring
When considering the molecular structure of local anesthetics, what determines hydrophilicity or the ability to accept a proton?
Tertiary amine
When considering the molecular structure of local anesthetics, what determines drug class, metabolism, and allergic potential?
Intermediate chain
What are examples of esters?
Benzocaine
Cocaine
Chloroprocaine
Procaine
Tetracaine
What are examples of Amides?
Bupivacaine
Dibucaine
Lidocaine
Mepivacaine
Ropivacaine
Amides have two “i”
How are ester local anesthetics metabolized?
Pseudocholinesterases
How are amide local anesthetics metabolized?
Hepatic clearance (P450)
Which local anesthetic class has cross sensitivity within its own class?
Esters
What is the equate to the following items? Think local anesthetics
Onset ~
Potency ~
Duration is action ~
Onset ~ pKa (also dose/concentration)
Potency ~ lipid solubility (intrinsic vasodilating effect)
Duration of action ~ protein binding (lipid solubility, addition of vasoconstrictors)
How do local anesthetics have a biphasic response on vascular smooth muscle?
At lower concentrations (below clinical use) they cause vasoconstriction
At higher concentrations (clinical use) they cause vasodilation.
Ionization is dependent on what two factors?
The pH of the solution
pKa of the drug
What is the pKa of Bupivacaine?
8.1
What is the pKa of Ropivacaine?
8.1
What is the pKa of Lidocaine?
7.9
What is the pKa of prilocaine?
7.9
What is the pKa of Mepivacaine?
7.6
What is the pKa of procaine?
8.9
What is the pKa of Chloroprocaine?
8.7
What is the pKa of tetracaine?
8.5
What is the pKa of benzocaine?
3.5!!
This is an odd man out!
What is a significant risk with benzocaine?
Methemoglobinemia
What are the levels of absorption of local anesthetics (from most to least)
What is the mnemonic
I Think I’ll Ingest cookies each Beautiful Friday for a Special Snack
I: IV
Think: Tracheal
I’ll: Interpleural
Ingest: Intercostal
Cookies: Caudal
Every: Epidural
Beautiful: Brachial Plexus
Friday: Femoral
For a
Special: Sciatic
Snack: subcutaneous
What protein to local anesthetics preferentially bind to?
Alpha 1-acid glycoproteins
How is exparel dispense and what is the max dose?
133 mg in 10 mL or 266 mg in 20 mL
Max dose: 266 mg
What are the rules for administering Lidocaine and exparel to a patient?
After administering lido —> no bupi for at least 20 mins
After administering Bupi —> no lido (in any form) for at least 96hours
What is the max dose (in both total dose and mg/kg) for Bupivacaine?
2.5 mg/kg
175 mg total
What is the max dose (in both total dose and mg/kg) for Bupivacaine with epi?
3 mg/kg
200 mg total
What is the max dose (in both total dose and mg/kg) for Ropivacaine?
3 mg/kg
200 mg total
What is the max dose (in both total dose and mg/kg) for Lidocaine?
4.5 mg/kg
300 mg
What is the max dose (in both total dose and mg/kg) for Mepivacaine?
7 mg/kg
400 mg total
What is the max dose (in both total dose and mg/kg) for Lidocaine with epi?
7 mg/kg
500 mg
What is the max dose (in both total dose and mg/kg) for Prilocaine?
8 mg/kg
< 70 kg ~ 500 mg
> 70 kg ~ 600 mg
What is the max dose (in both total dose and mg/kg) for Procaine?
7 mg/kg
350 - 600 mg total
What is the max dose (in both total dose and mg/kg) for Chloroprocaine?
11 mg/kg
800 mg total
What is the max dose (in both total dose and mg/kg) for Chloroprocaine and with Epi?
14 mg/kg
1,000 mg total
What is the most common cause of toxic plasma concentrations?
Inadvertent intravascular injection
Is LAST more common with peripheral nerve blocks or epidural anesthesia?
Peripheral nerve blocks
At what plasma concentration of Lido would you see analgesia?
1-5 mcg/mL
At what plasma level of lidocaine do you see tinnitus, numbness, and/or blurred vision? AND hypotension/cardiac depression?!
5-10 mcg/mL
At what plasma level of Lido do you see seizures and/or LOC?
10-15 mcg/mL
At what plasma level of lidocaine do you see coma and/resp arrest?
15-25
What are factors that increase CNS toxicity with local anesthetics?
Hypercarbia —> increased Blood flow
Acidosis —> decreases convulsion threshold
Hyperkalemia —> raises RMP
What factors decreases CNS effects?
Hypocarbia —> decrease cerebral blood flow
Hypokalemia —> decreases resting membrane potential
CNS depressants —> raise seizure threshold
Which local anesthetic has a greater affinity of voltage gated sodium channel receptors in the heart?
Bupivacaine > Levobupivacaine > Ropivacaine >Lidocaine
What is the primary risk of cocaine toxicity?
Excessive SNS stimulation
What is the dose for cocaine? Mg/kg and max?
1.5-3 mg/kg
150-200 mg total
In terms of LAST, what should be avoided as far as vasopressors?
Avoid vasopressin
Keep epi dose low 1mcg/kg
What is the 20% lipid emulsion therapy for someone > 70 kg
Bolus: 100 mL over 2-3 minutes
Infusion: 250 mL over 15-20
What is the 20% lipid emulsion therapy for someone < 70 kg
Bolus: 1.5 mL over 2-3 minutes
Infusion: 0.25 mL/kg/min
What is the maximum dose of lidocaine during tumescent anesthesia?
55 mg/kg
What is the most common cause of death in liposuction?
PE
When is general anesthesia recommended when administering a tumescent infusion?
> 2-3 L
What are some causes of acquired methemoglobinemia? Local anesthetics
Benzocaine (also bupi is in Cetacaine)
Prilocaine (together with Lido = EMLA)
Lidocaine
What is the light waveform for deoxygenated blood?
Red 660
What is the light waveform for oxygenated blood?
Infrared 940
What is the light absorption for methemoglobin?
Both Red 660 AND infrared 940!!
What are the key findings in methemoglobinemia?
Decreased SpO2 (usually 85%)
Normal PaO2
What is the treatment to methemoglobinemia? What is the dose?
Methylene blue 1-2 mg/kg
When does methemoglobinemia occur? MOA?
It’s produced when the iron molecule becomes oxidized to its ferric form (Fe 3+)
How does methemoglobin affect the oxyhemoglobin curve?
Shifts to the left
What are some S&S of methemoglobinemia?
Chocolate colored blood
Hypoxia
Cyanosis (slate grey pseudocyanosis)
What is the max dose of EMLA?
0-3 months (<5kg): 1 g
3-12 months (>5kg): 2 g
1-6 years (>10kg): 10 g
7-12 years (>20kg): 20g
What drugs prolong the duration of action of local anesthetics?
Epinephrine
Decadron
Dextran
What drugs provide supplemental analgesia to local anesthetics?
Clonidine
Epinephrine
Opioids
What drugs shorten onset time of local anesthetics?
Sodium bicarb
