Local Anesthetics

Question 1

What local anesthetic class is responsible for more allergic reactions?

Answer 1

Esters (due to PABA metabolite)

Question 2

What is LAST?

Answer 2

Local Anesthetic Systemic Toxicity

Question 3

What causes LAST syndrome?

Answer 3

Excess plasma concentration of LA from:

• Accidental IV injection
• Systemic absorption from tissue redistribution and clearance metabolism.

Question 4

What factors affect the magnitude of systemic absorption of local anesthetic?

Answer 4

• Dose
• Vascularity of site
• Concurrent Epi use
• Properties of the drug itself

Question 5

Would local anesthetic administered via the trachea have a higher or lower chance of systemic absorption than local anesthetic delivered brachially?

Answer 5

Trachea has higher chance of systemic absorption.

Question 6

What serum electrolyte condition will exacerbate local anesthetic toxicity?
Why?

Answer 6

Hyperkalemia (lowers seizure threshold)

Question 7

What s/s would be seen with a plasma lidocaine concentration of 1-5 mcg/ml?

Answer 7

Analgesia

Question 8

What s/s would be seen with a plasma lidocaine concentration of 5-10 mcg/ml?

Answer 8

• Mouth numbness
• Tinnitus
• Muscle twitching
• ↓BP
• Myocardial depression

Question 9

What s/s would be seen with a plasma lidocaine concentration of 10-15 mcg/ml?

Answer 9

• Seizures
• Unconsciousness

Question 10

What s/s would be seen with a plasma lidocaine concentration of 15-25 mcg/ml?

Answer 10

• Apnea
• Coma

Question 11

What s/s would be seen with a plasma lidocaine concentration of >25 mcg/ml?

Answer 11

Cardiovascular Depression

Question 12

How does lidocaine affect EKGs?
How does it do this?

Answer 12

• Prolongation of PR interval and QRS widening.
• Blockade of Na⁺ channels

Question 13

Which three drugs are most responsible for cardiac adverse effects when reaching toxic levels systemically?

Answer 13

Bupivacaine > Ropivacaine > Lidocaine

Question 14

How does Lipid Emulsion rescue work?

Answer 14

Lipids encapsulate the local anesthetic and transport it away from cardiac and CNS tissue.

Also provides fat for myocardial metabolism.

Question 15

What is the bolus dose of Lipid Emulsion?

Answer 15

1.5 mL/kg of 20% lipid emulsion

Question 16

What is the infusion dose of lipid emulsion?
How long should it be given?

Answer 16

0.25 mL/kg/minute for at least 10 minutes

Question 17

What is the max dose for lipid emulsion that should be given?

Answer 17

8 mL/kg

Question 18

What preservative commonly used for amide local anesthetics canbe responsible for allergies?

Answer 18

Methylparaben

Question 19

Why does pregnancy predispose one to cardiovascular toxicity from LA’s?

Answer 19

Pregnancy = ↓ plasma cholinesterases

Question 20

Which two factors predispose our OB population to local anesthetic toxicity?

Answer 20

• ↓ plasma esterases
• ↓ plasma proteins

Question 21

Should a local anesthetic toxicity patient be hyperventilated or hypoventilated?
Why?

Answer 21

Hyperventilation = ↓ CO₂ = ↓ acidosis

Question 22

If cardiac arrest occurs with LAST syndrome, how should our epinephrine dosing change?

Answer 22

Small doses (10mcg - 100mcg boluses) are preferred with LAST ACLS.

Question 23

How much vasopressin should be given if a patient is suffering from hypotension from LAST syndrome?

Answer 23

Trick question. Vasopression should not be given with LAST syndrome.

Question 24

Answer 24

56kg so 1.5mLs x 56kg = 84mLs

20% infusion = 200mgs / 1mL

84mLs x 200mgs = 16,800mgs administered

Question 25

What is Cocaine's MOA?

Answer 25

Blocks presynaptic re-uptake of NE and Dopamine → Increases postsynaptic levels and ↑SNS.

Question 26

What drug is best for treating cocaine toxicity?

Answer 26

Nitroprusside

Question 28

If Drug V (weak base) has a pKa of 9.1, will the drug be more ionized or nonionized at physiological pH?

Answer 28

pKa - pH 9.1 - 7.4 = +1.7 Drug V will be more ionized at physiological pH. *Weak Bases, pKa **before** pH* *Weak Acids, pKa **after**pH*

Question 29

If the pKa of LA (a weak base) is at 4.5, will the drug be more ionized or nonionized at physiological pH?

Answer 29

pKa - pH 4.5 - 7.4 = -2.9 LA will be more non-ionized at physiological pH. *Weak Bases, pKa **before** pH* *Weak Acids, pKa **after**pH*

Question 30

LA1's pKa is 9.2, and LA2's pKa is 7.5. Which of the following are correct when placed in physiological pH? Select 2 answers. A. LA2 has more non-ionized components B. LA1 has more ionized components C. LA2 has more ionized components D. LA1 has more non-ionized components

Answer 30

B and C LA1 9.2 - 7.4 = +1.8 (ionized) LA2 7.5 - 7.4 = +0.1 (ionized) *Weak Bases, pKa **before** pH* *Weak Acids, pKa **after**pH*

Question 31

What is epinephrine 1:200,000 mean? Convert that to mcg/mL.

Answer 31

1:200,000 means 1 gram of epinephrine is dissolved in 200,000 mL of solvent. * 1g/200,000 mL * 1000mg/200,000 mL * 1 mg/200 mL * 1000 mcg/200 mL * 10 mcg/2 mL * **5 mcg/mL**

Question 32

Compute 1:500,000 to mcg/mL

Answer 32

2 mcg/mL * 1 g/500,000 mL * 1000 mg/500,000 mL * 1 mg /500 mL * 1000 mcg/500 mL * 10 mcg/5 mL * 2 mcg/mL *Shortcut: 1,000,000 divided by the solvent number. 1 million/500,000 = 2 mcg/mL*

Question 33

Compute 1:500,000 Epi to mcg/mL

Answer 33

1,000,000/ 500,000=2 **2 mcg/mL**

Question 34

Compute 1:10,000 Epi to mcg/mL

Answer 34

1,000,000/ 10,000 = 100 **100 mcg/mL**

Question 35

Compute 1:1000 Epi to mcg/mL

Answer 35

1,000,000/ 1000 = 1000 **1000 mcg/mL**

Question 36

0.25% equates to how many mg per mL ?

Answer 36

2.5 mg/mL

Question 37

0.5% equates to how many milligrams per milliliter?

Answer 37

5 mg/mL

Question 38

1% equates to how many milligrams per mL ?

Answer 38

10 mg/mL

Question 39

2% equates to how many milligrams per mL ?

Answer 39

20 mg/mL *2% lidocaine is the most common concentration used in the OR*

Question 40

4% equates to how many milligrams per mL ?

Answer 40

40 mg/mL

Question 41

112.5 mg of Bupivacaine with Epi and 250 mg of Lidocaine with Epi were given during surgery. What are the percentages of each LA based on the recommended max single dose in mg?

Answer 41

Max single dose of Bupivacaine with Epi: 225 mg 112.5/225 = 50% Max single dose of Lidocaine with Epi: 500 mg 250/500 = 50%

Question 42

When the peripheral nerve block is wearing off, what comes back first? Proximal or Distal?

Answer 42

Proximal comes back first & then distal.

Question 43

Peripheral Nerve Block onset of action is dependent on the local anesthetic's _________.

Answer 43

pK

Question 44

The duration of a peripheral nerve block depends on the _____ of the local anesthetic.

Answer 44

dose

Question 45

What is the sequence of blockades for a segmental block in Neuraxial Anesthesia?

Answer 45

1. SNS (Myelinated preganglionic B fibers) 2. Sensory (Myelinated A, B fibers, unmyelinated C fibers) 3. Motor (Myelinated A-δ and unmyelinated C fibers)

Question 46

For SAB, the _______ effect is 2 spinal segments cephalad of the sensory block. For SAB, the _______ effect is 2 spinal segments below the sensory block.

Answer 46

SNS Motor

Question 47

What can be added to LA so that its specific gravity can increase? What can be added to LA so that its specific gravity can decrease?

Answer 47

Glucose added → hyperbaric solution. Distilled water added → hypobaric solution

Question 48

Regarding weak bases, the pKa is ________ pH.

Answer 48

before ex. pKa 9, pH 7 → 9 - 7 = +2

Question 49

Regarding weak acids, the pKa is ________ pH.

Answer 49

after ex. pKa 9, pH 7 → 7 - 9 = -2

Question 50

Nicely negative numbers are _________.

Answer 50

non-ionized