Local Anaesthesia

Question 1

What do local anaesthetic (LA) agents do?

Answer 1

They reversibly block the transmission of peripheral nerve impulses.

Question 2

What are examples of physical factors that can cause reversible nerve block?

Answer 2

Pressure and cold.

Question 3

What was the first local anaesthetic, and when was it discovered?

Answer 3

Cocaine, discovered in 1860 from Erythroxylum coca.

Question 4

Who demonstrated the first LA action of cocaine, and when?

Answer 4

Koller in 1864.

Question 5

Why is cocaine’s use as an LA limited?

Answer 5

Due to allergic reactions.

Question 6

When was procaine first synthesised?

Answer 6

Procaine was synthesised in 1904.

Question 7

Which LA was synthesised in 1943?

Answer 7

Lidocaine.

Question 8

List the LAs synthesised from 1957 to 2000.

Answer 8

Mepivacaine (1957), prilocaine (1960), bupivacaine (1963), ropivacaine (1997), levobupivacaine (2000).

Question 9

What types of LAs are popular in North America?

Answer 9

Ester LAs (e.g., cocaine, procaine, chloroprocaine).

Question 10

What limits the use of ester LAs in North America?

Answer 10

Due to potential allergic reactions.

Question 11

How are LAs classified based on their physical structure?

Answer 11

Based on ester and amide structures.

Question 12

What type of linkage do ester and amide LAs have?

Answer 12

Esters have an ester linkage, and amides have an amide linkage.

Question 13

List examples of ester LAs.

Answer 13

Cocaine, procaine, amethocaine, chloroprocaine.

Question 14

List examples of amide LAs.

Answer 14

Lidocaine, mepivacaine, prilocaine, bupivacaine, ropivacaine, levobupivacaine.

Question 15

How are LAs classified based on potency and duration of action?

Answer 15

Based on their potency and duration of action.

Question 16

What LAs have a short duration of action and low potency?

Answer 16

Procaine and chloroprocaine.

Question 17

Which LAs have intermediate potency and duration?

Answer 17

Lidocaine, mepivacaine, prilocaine, cocaine.

Question 18

Name LAs with long duration of action and high potency.

Answer 18

Bupivacaine, tetracaine, etidocaine.

Question 19

How do ester LAs differ from amide LAs in terms of stability?

Answer 19

Esters hydrolyse spontaneously and can be heat-sterilised once; amides are more stable.

Question 20

What factors increase the duration of action of LAs?

Answer 20

Lipid solubility, protein binding affinity, and type of nerve fibre.

Question 21

What factors influence the potency of LAs?

Answer 21

Lipid solubility.

Question 22

How is the rate of onset of LA action determined?

Answer 22

By the pKa of the LA; lower pKa leads to faster onset.

Question 23

What factors affect the pharmacokinetics of LAs?

Answer 23

Absorption kinetics, distribution, dosage, injection site, and physiological factors.

Question 24

Which factors influence the absorption kinetics of LAs?

Answer 24

Physicochemical properties, dosage, injection route, vasoconstrictors, and pathophysiological factors.

Question 25

How does pregnancy affect the pharmacokinetics of LAs?

Answer 25

It increases the segmental spread of epidurals.

Question 26

How does the site of injection affect the rate of LA absorption?

Answer 26

It is influenced by the rate of blood flow to different nerves and tissues.

Question 27

What happens if the IVRA tourniquet is released prematurely?

Answer 27

It causes rapid entry of a large dose into circulation.

Question 28

How are ester LAs metabolised?

Answer 28

They undergo hydrolysis by plasma cholinesterase.

Question 29

How are amide LAs metabolised?

Answer 29

They are metabolised in the liver, with prilocaine undergoing some extra-hepatic metabolism.

Question 30

What is the function of additives to LAs?

Answer 30

To adjust pH, tonicity, baricity, and for pharmacologic reasons.