Quiz 4 Local Anesthetics

Question 1

Where do local anesthetics (LA) have a better access to the axon on myelinated nerves?

Answer 1

at the Nodes of Ranvier

Question 2

What channels do LA work on to block signals on a nerve axon?

Answer 2

Na+ channels

Question 3

Local anesthetics are greatly facilitated if the drug is in the ____________ or _________ state

Answer 3

Uncharged or non-ionized state

Question 4

What is a quick way of telling whether the LA is an amide or ester anesthetic?

Answer 4

The Amides have 2 “i” in the name, ex. Lidocaine, Ropivacaine….

Question 5

What correlates well with the LA’s potency?

Answer 5

Lipid solubility

Question 6

What are some factors that affect the minimum blocking concentration of a LA?

Answer 6

• Fiber size
• fiber type
• myelination
• pH of tissues
• pKa of LA

Question 7

T/F - a LA with a pKa closer to physiologic pH will have a higher concentration of IONZED form and can readily pass through the nerve cell membrane.

Answer 7

False - non-ionized

Question 8

Why do LA’s with higher lipid solubility have greater potency?

Answer 8

they are less likely to be cleared by blood flow

Question 9

Which Amides have the highest and lowest potency?

Answer 9

Highest - Bupivacaine (duration 200+ min)

Lowest - Mepivacaine (duration 45-90 min)

Question 10

Which Ester has the highest potency?

Answer 10

Tetracaine (duration 200+ min)

Question 11

What are 2 factors that will help determine the sensitivity of the nerve to a LA?

Answer 11

1. Axonal Diameter: Small > Large

2. Myelination: Unmyelinated > myelinated

Question 12

In spinal nerves, which is most sensitive to local anesthetics: Autonomic, sensory, or motor?

Answer 12

Autonomic is most sensitive.

Autonomic > Sensory > Motor

Question 13

Systemic absorption of LA depends on what?

Answer 13

• blood flow to area being injected
• vasoconstrictors
• specific LA agent (high or low lipid solubility)

Question 14

Which LA is the only one to not produce relaxation of vascular smooth muscle?

Answer 14

Cocaine - causes vasoconstriction which makes it great for nosebleeds and ENT procedures

Question 15

If most LA’s cause relaxation of vascular smooth muscle, what could happen to your anesthetic?

Answer 15

• increased absorption
• decreased duration of action
• increased probability of systemic/toxic effects

Question 16

How are Esters metabolized?

Answer 16

By pseuodcholinesterase, water soluble metabolites excreted through urine

Question 17

Which 2 esters are metabolized by PABA and associated with allergic reactions?

Answer 17

Procaine and benzocaine

Question 18

How are Amides metabolized?

Answer 18

P-450 and metabolism is slower than with Esters but are excreted through urine, also.

**Decrease in liver fxn will reduce metabolism and increase toxicity”

Question 19

What are 2 LA’s that are implicated for causing methemoglobinemia?

Answer 19

Prilocaine - amide
Benzocaine spray - ester

++Treat with methylene blue

Question 20

T/F: The slower a local anesthetic is absorbed into the vascular space, the less likely that high blood levels and subsequent CNS or cardiac toxicity will occur.

Answer 20

True

Question 21

If you have 1% lidocaine, what is the concentration of that drug? (g/ml)

Answer 21

1 gram per 100 ml

Question 22

What environments will cause ion trapping and what will it do to anesthetics?

Answer 22

• Acidosis, injection into acidotic/infected tissues, septic pts
• causes higher accumulation of drug, which will prolong duration of action

Question 23

Effects of LA on CNS?

Effects of LA on cardiovascular?

Answer 23

CNS - convulsions - increased O2 consumption in presence of compromised ventilation
Cardiovascular - depresses automaticity, reduced refractory period, depressed contractility/conduction, vasodilation,

Bradycardia -> heart block -> hypotension -> cardiac arrest

Question 24

How long do you need to leave EMLA cream on to get satisfactory analgesia?

Answer 24

1 hr covered in occlusive dressing

Question 25

What sites are good for topical anesthesia?

Answer 25

Mucus Membranes: nose, mouth, tracheobronchial tree, esophagus, GU tract

**absorption of LA through Mucus Membranes is significant and can cause systemic toxicity

Question 26

What sites should you NOT use epinephrine in your LA’s?

Answer 26

Should NOT be injected around end arteries like:

• fingers/toes
• Ears/Nose
• Genitals

Question 27

What are concentrations of LA used for infiltration?
Lidocaine -
Procaine -
Bupivacaine -

Answer 27

Lido - 0.5 - 1%
Pro - 0.5 - 1%
Bupiv - 0.125 - 0.25%

Question 28

What is Transient Neuologic Symptoms (TNS)?

Answer 28

dyesthesia, burning pain, and aching in lower extremities/buttocks associated with use of lidocaine in spinal

Question 29

Methemoglobinemia becomes an issue in patient’s with severe ________ or ________ failure.

Answer 29

anemia, heart