Local Anaesthetics

Question 1

What are local anaesthetics?

Answer 1

Drugs that reversibly block nerve conduction when applied to a restricted area of the body, without loss of consciousness
(they don’t stop pain, they just block it)

Question 2

What is perception?

Answer 2

when the info reaches the brain

Question 3

What is the basic structure of a local aesthetic?

Answer 3

A benzene ring linked to a R group linked to NH2

Question 4

What is the linkage and what does it do?

Answer 4

-amide or ester
linkage determines how fast the drug is broken down and leaves the body
-ester faster than amide
-this means that you can control how long the anaesthetic works for

Question 5

what are the longest and shortest duration?

Answer 5

procaine/cocaine= shortest
bupivacaine = longest

Question 6

Why is the benzene ring important?

Answer 6

lipid soluble so allows drug to move into cells

Question 7

Why is the amide part important

Answer 7

• it is neutral but if its protonated it becomes positively charged
• therefore one part of the molecule os lipid soluble and the other part isn’t lipid soluble

Question 8

What is the use dependent block?

Answer 8

• the protonated form of weak acids blocks open channels or recently active inactivated sodium channels
• this means drug only targets channels in the neurones that are very active so the amount of pain is matched by the amount of block because the more noxious stimulus there is the more action potentials there are so more blocking occurs

Question 9

What are the factors that affect effectiveness of a local anaesthetic?

Answer 9

• tissue PH
• inflammation and infection
• width of diameter of axons (small diameter easier)

Question 10

What are the high sensitivity types of axons?

Answer 10

Adelta

C type

Question 11

What are the methods of admin of LA?

Answer 11

• topical
• infiltration anaesthesia
• nerve block
• epidural
• spinal

Question 12

What is topical and how effective?

Answer 12

• drug diffuses through cell layers

- not v effective

Question 13

What is infiltration?

Answer 13

-injections surrounding the nerve terminals of nociceptor neurones

Question 14

What is nerve block?

Answer 14

as axons branch an injection is made (injecting higher up before more branches allows you to cover a larger area)

Question 15

What is spinal?

Answer 15

injection into fluid surrounding the spinal cord

Question 16

What is epidural?

Answer 16

injected into epidural space the outside of the spinal cord so as nerves leave they are bathed in anaesthetic

Question 17

What are the unwanted effects of LA?

Answer 17

Non-specific:
-hypersensivity to other components in anaesthetic
specific:
in high doses it may stop needed action potentials from occurring
Affect on other excitable tissues:
-CNS can cause tremors, convulsions and respiratory failure

CV system:

• decrease contractility of cardiac muscle
• dilate blood vessels
• lower BP

Question 18

What are the other drugs administered with LA?

Answer 18

-vasoconstrictors (e.g adrenaline, localise LA by stopping blood flow in the areas we don’t want it stopping anaesthetic from spreading to unwanted areas)

Question 19

What are the properties of a good local anaesthetic?

Answer 19

• decrease unwanted effects

- increase duration of action