Local Anaesthetics (General)

Question 1

What does a Local Anaesthetic do?

Answer 1

Blocks peripheral nerve conduction and all sensation (Blocks Pain Too)

Question 2

Does Local Anesthetic block pain?

Answer 2

Yes they do

Question 3

Do Local Anesthetics result in loss of consciousness?

Answer 3

No does not

Question 4

How can a Local Anesthetic be applied?

Answer 4

Topically
Parentally
Intravenously

Question 5

Chemistry of Local Anesthetics (What kind of functional groups can it contain?)

Answer 5

Aromatic Residue + Linkage + Basic Amine
Linkage can be:
Ester
Amide

Question 6

Local Anesthetics with Ester Linkage

Answer 6

Quickly inactivated by plasma & tissue esterases

Question 7

Local Anesthetic with Amides Linkage

Answer 7

More stable and a longer half life
Metabolized by liver

Question 8

Local Anesthetic with no Amino Group

Answer 8

Benzocaine

Aromatic Residue + Ester + Ethyl

Question 9

Local Anesthetic (Acid/Base)

Answer 9

Weak Basics

Question 10

Local Anesthetic (Salts)

Answer 10

Provided as salts (Usually HCl)

Question 11

Local Anesthetic (What two forms exist in Equilibrium)

Answer 11

Cationic Form
Uncharged Form

Question 12

Local Anesthetic Cationic Form

Answer 12

Active Form

Question 13

Local Anesthetic Uncharged Form

Answer 13

Membrane Permeable Form

Question 14

Local Anesthetic (What does increasing pKa)

Answer 14

Greater pKa = Greater ratio of cationic to uncharged

More cationic form –> Slower rate of anaesthesia onset

Question 15

Local Anesthetic (Mechanism of Action: What does it target?)

Answer 15

Blocks Na+ Channel
–> Increases the excitation threshold
–> Block conduction

Can act on new nerve endings making it harder for them to achieve action potential

Question 16

Local Anesthetic (Mechanism of Action: Passing Membrane)

Answer 16

Local Anesthetic must be in its uncharged form to pass through membrane
(Hydrophobic Pathway)

It then gets reionized and enters the channel from the inside
–> If channel is already open cationic form can enter and bind

Question 17

Effect of low pH on Local Anesthesia

Answer 17

Lower pH = More acidic = Equilibrium shifts to the cationic form (Charged Form) = Unable to cross the membrane

–> Reduces the effect

Question 18

Effect of activity on Local Anesthesia

Answer 18

The more active the nerve = Channel is open and can bind to cationic form –> More rapid block develops

Question 19

Characteristics of a Sensory Pain Fibre

Answer 19

Thin
High Firing Rates
Long Broad AP Durations

Question 20

Nerve Fibers and Susceptibility to Local Anesthetic

Answer 20

Fiber Diameter
- Smaller = More Susceptible

Firing Frequency
- Higher Frequency = More likely to be blocked
Use-dependence

AP Potential Duration
- Broad spikes are in activated state longer = More likely for anesthetic to enter channel

Question 21

Local Anaesthetic (Unwanted Effects: Toxic Effects)

Answer 21

Systemic Absorption can lead to toxic effects

Question 22

Local Anaesthetic (Unwanted Effects: CV)

Answer 22

Cardiac Depression –> Inhibition of Na+ in cardiac muscle
Hypotension –> Inhibition of sympathetic

Question 23

Local Anaesthetic (Unwanted Effects: CV)
- Exception

Answer 23

Cocaine does not cause cardiac depression as it targets NE reuptake

Question 24

Local Anaesthetic (Unwanted Effects: CNS)

Answer 24

Sleepiness (Lowest Concentration)
Convulsions (Medium Concentration)
CNS Depression (Highest Concentration)

More Local Anaesthesia used = More CNS issues

Question 25

Local Anaesthesia + Vasoconstrictor

Answer 25

Add epinephrine to Local Anesthetic

Decreases Systemic Absorption –> Increases Local Anaesthesia Concentration at site

Counteracts Local Anaesthesia Vasodilation action