Chapter 115-116: Local anesthetics-

Question 1

What is the structure of a local anesthetic?

Answer 1

Aromatic lipophilic end connected to hydrophilic tertiary amine VIA AN INTERMEDIATE CHAIN that is either an ester or amide

Question 2

Compare the differences between the ionized form and the nonionized form of a local anesthetic in terms of how each works to cause the desired effect of local anesthetics

Answer 2

The nonionized form will cross the lipid membrane. Because the intracellular pH is closer to 7, once the local anesthetic agent crosses the cell membrane it will become the ionized form. It is the ionized form that is able to bind with the alpha subunit of the na channel to inactive it.

Question 3

Which properties of a local anesthetic will cause the onset time to be fast?

Answer 3

1) more lipophilic drugs have faster onset because they cross the cell membrane more readily.
2) Compounds have have pKA closer to physiologic pH will also have quicker onset.

Question 4

How are ester local anesthetics metabolized?

Answer 4

pseudocholinesterases and partially be red blood cell esterases

Question 5

How are amide local anesthetics metabolized?

Answer 5

hepatic pathway

Question 6

What characteristic of local anesthetics are responsible for potency?

Answer 6

lipid solubility- the more soluble an agent is, the more readily it crosses into the axon

Question 7

Which class of local anesthetic are there more allergic reactions?

Answer 7

The ester class because pseudocholinesterase causes hydrolysis to occcr and yields para-amiobenzoic acic (PABA)

Question 8

How do the following ester local anesthetics compare in terms of duration? Tetracaine, procaine, chloroprocaine

Answer 8

Chloroprocaine is hydrolyzed 4x faster than procaine

Procaine is hydrolyzed 4x faster than tetracaine

Question 9

How are amide local anesthetics metabolized?

Answer 9

Through the liver via 1) aromatic hydroxylation 2) N-dealkylation and 3) amide hydrolysis

Question 10

Which amide local anesthetic has metabolism outside of the liver?

Answer 10

Prilocaine is metabolized by extrahepatic tissues

Question 11

Which local anesthetics have had problems with methemoglobinemia? What is the treatment?

Answer 11

Benzocaine (because it insoluble in water, limited to topical use).
Prilocaine (used in EMLA)- metabolized to o-toluidine

Treatment is methylene blue- 1mg/kg.

Question 12

Which locations are most worrisome for local anesthetic absorption?

Answer 12

Intravenous> Intercostal > Caudal > Lumbar epidural > brachial plexus > subcutaneous

Question 13

What is the max dose and duration of effect of chloroprocaine?

Answer 13

12 mg/kg, up to 1 hour

Question 14

What is the max dose and duration of effect of procaine?

Answer 14

12 mg/kg, up to 1 hour

Question 15

What is the max dose and duration of effect of cocaine?

Answer 15

3 mg/kg, up to 1 hour

Question 16

What is the max dose and duration of effect of tetracaine?

Answer 16

3 mg/kg up to 6 hour

Question 17

What is the max dose and duration of effect of lidocaine?

Answer 17

4.5 mg/kg without epi, 7 mg/kg with epi, 1.5 hours

Question 18

What is the max dose and duration of effect of prilocaine?

Answer 18

8 mg/kg, 1 hour

Question 19

What is the max dose and duration of effect of mepivicaine?

Answer 19

4.5 mg/kg without epi, 7 mg/kg with epi, 2 hours

Question 20

What is the max dose and duration of effect of bupivacaine?

Answer 20

3 mg/kg, 8 hours

Question 21

What is the max dose and duration of effect of ropivacaine?

Answer 21

3 mg/kg, 8 hours

Question 22

What is the cardiovasular effects of all local anesthetics?

Answer 22

decreased myocardial contractility and vasodilate (all except cocaine which causes vasoconstriction by acting as norephinepherine reuptake inhibitor)

Question 23

What is the dose of lipids that should be given for LA toxicity?

Answer 23

20% lipid infusion should be dose 1.5-4 mL/kg bolus then 0.5mL/kg infusion.

Question 24

Which LA have been implicated in cauda equina syndrome?

Answer 24

Chloroprocaine and lidocaine, especially with the intrathecal microcatheters

Question 25

What is transient neurologic symptoms, what are the associated factors and which drugs are implicated in this?

Answer 25

severe pan radiating down both legs
factors: lithotomy position, early ambulation, obesity
LA: lidocaine

Question 26

What does the American Academy of Dermatology set as the max safe dose of lidocaine for liposuction? When is toxicity likely to occur?

Answer 26

55 mg/kg

Because absorption of lidocaine is delayed in the fatty tissue, most toxicity reactions occur 6-12 hours after the procedure.

Question 27

What are the 3 most common LA preservatives, what is their function and what are the possible toxic reactions associated with them?

Answer 27

Sulfite- antioxidant- arachnoiditis and anaphylactoid reaction

EDTA- chelating agent, low back pain at site of injection 2/2 to lumbar paraspinal muscle spasm

Parabens- antimicrobial- chemical structure similiar to PABA, may get anaphylactoid reaction