Local Anesthetics

Question 1

Are local anesthetics weak acids or weak bases?

Answer 1

• weak bases

Question 2

What is the pKa of benzocaine?

Answer 2

• 3.5
• it is unionized at physiologic pH
• it is useful for topical anesthesia during endoscopy, TEE, and bronchoscopy

Question 3

What is the most common cause of toxic plasma concentrations of LA?

Answer 3

inadvertent intravascular injection during regional anesthesia

Question 4

What is the most frequent symptom of toxic plasma concentrations of LA?

Answer 4

• seizures

- bupivacaine is the exception - can cause cardiac arrest before seizure

Question 5

What type of regional anesthesia is LAST more common with?

Answer 5

• more common with peripheral nerve blocks than epidurals

Question 6

What are factors that increase CNS local anesthetic toxicity?

Answer 6

• hypercarbia
• hyperkalemia
• metabolic acidosis

Question 7

What are factors that decrease CNS local anesthetic toxicity risk?

Answer 7

• hypocarbia
• hypokalemia
• CNS depressants

Question 8

What is the order of difficulty in cardiac resuscitation with LAs?

Answer 8

bupivacaine>levobupivacaine>ropivacaine>lidocaine

Question 9

The risk of bupivacaine toxicity is increased with?

Answer 9

• pregnancy
• beta blockers
• calcium channel blockers
• digitalis

Question 10

What is the primary risk of cocaine toxicity?

Answer 10

• excessive SNS stimulation

Question 11

Cocaine should be avoided with what drugs?

Answer 11

• MAOIs
• TCA
• sympathomimetics

Question 12

What is important about giving beta blockers in the setting of cocaine overdose?

Answer 12

• it allows for unopposed alpha-1 stimulation (inc SVR) and dec. inotropy (beta-1 antagonism) which can lead to cardiovascular collapse
• vasodilator such as nitroglycerine is best
• labetolol (or another mixed alpha & beta antagonist)

Question 13

What is the treatment for LAST?

Answer 13

• manage the airway (110% FiO2)
• treat with benzos (or Succs, NDNMB,)
• avoid propofol d/t augmentation of myocardial depression
• Epi can hinder resuscitation from LAST and dec. effectiveness of lipid emulsion (if needed use < 1 mcg/kg)
• avoid vasopressin
• for ventricular arrhythmia give amiodarone (not lidocaine or procainamide)
• lipid emulsion bolus of 20% 1.5 mL/kg (infusion = 0.25 mL/kg/min)

Question 14

What does the solution for tumescent anesthesia consist of?

Answer 14

• dilute solution of sodium chloride
• lidocaine
• epi
• bicarb

Question 15

What is the maximum dose of lidocaine for tumescent anesthesia?

Answer 15

• 55 mg/kg

Question 16

When is general anesthesia recommended for tumescent anesthesia?

Answer 16

> 2-3 L of tumescent are injected

Question 17

What local anesthetics are most likely to produce methemoglobinemia?

Answer 17

• cetacaine
• benzocaine
• EMLA cream

Question 18

What other drugs can cause methemoglobinemia?

Answer 18

• nitroprusside
• nitroglycerine
• sulfonamides
• phenytoin

Question 19

What is the treatment for methemoglobinemia?

Answer 19

• methylene blue 1-2 mg/kg
• its with glucose-6-phosphate reductase deficiency do not possess methemoglobin reductase and an exchange infusion may be required

Question 20

How long does EMLA cream take to produce analgesia?

Answer 20

• 1 hr

- 2-3 hr for maximum effect

Question 21

What can be applied to hasten the absorption of EMLA cream?

Answer 21

• nitroglycerine