Local anaesthetics :p2

Question 1

What are the disadvantages of epidural LA over spinal LA?

Answer 1

Slower onset Higher doses need to be used More restricted action - less effect on BP

Question 2

When may nerve block LA be used?

Answer 2

Dental work

Question 3

What is co-injected with nerve block LA?

Answer 3

A vasoconstrictor

Question 4

Where is nerve block LA injected?

Answer 4

Close to target nerve trunks

Question 5

Are LAs acids or bases?

Answer 5

Weak bases PKa 8-9

Question 6

What are the effects of local anaesthetics?

Answer 6

• Prevent generation and conduction of action potentials - May influence channel gating - Selectively block nociceptive pain fibres - small diameter fibres (A-delta and C-neurones have small diameter axons), non-myelinated fibres (pain C fibres)

Question 7

Do LAs influence resting membrane potential?

Answer 7

No

Question 8

Why is infected tissue harder to anaesthetise?

Answer 8

Infected tissue tends to be acidic Larger proportion of LA in ionised state (BH+)

Question 9

What are the side effects of spinal anaesthesia?

Answer 9

Decreased BP Prolonged headache

Question 10

What are the pharmacokinetics of lidocaine?

Answer 10

• Good absorption at mucous membranes - 70% plasma protein binding - Hepatic metabolism by N-dealkylation - Plasma half life = 2 hours

Question 11

What are the pharmacokinetics of cocaine?

Answer 11

• Good absorption at mucous membranes - 90% plasma protein binding - Hepatic and plasma metabolism by non-specific esterases - Plasma half life = 1 hour

Question 12

Compare the plasma half lives of lidocaine and cocaine

Answer 12

Lidocaine = 2 hours Cocaine = 1 hour

Question 13

Compare the absorption at mucous membranes of lidocaine and cocaine

Answer 13

Both good

Question 14

Compare the plasma protein binding of lidocaine and cocaine

Answer 14

Lidocaine = 70% Cocaine = 90%