Pharmacology and local anaesthetics

Question 1

What is local anaesthesia

Answer 1

A loss of feeling restricted to a particular region

Question 2

Why is local anaesthesia used

Answer 2

• To enable minor or major operative procedures to be carried out
• to provide relief from prolonged severe pain

Question 3

How can local anaesthesia be produced

Answer 3

• Cooling with ethyl chloride
• Pressure
• Hypoxia
• Irreversible blockade

Question 4

How do local anaesthetics work

Answer 4

Reversibly block impulse conduction along nerve axons and other excitable membranes that utilise sodium channels as the primary means of action potential generation

Question 5

How does local anaesthetic work with sodium ion channels

Answer 5

Local anaesthetic drugs act mainly by inhibiting Na+ influx through voltage-gated sodium channels

Question 6

Describe the mechanism of action

Answer 6

1. As charge spreads down an axon, myelination prevents ions from leaking out across the plasma membrane
2. Charge spreads until it reaches an unmyelinated section of axon (node of Ranvier) which is packed with Na+ channels
3. Electrical signals continue to jump down the axon much faster than they can move down an unmyelinated cell

Question 7

What are major determinants for the diffusion of anaesthetic solution to the nerve fibres

Answer 7

• Site of administration
• Drug

Question 8

What’s the effect of acidosis on local anaesthetic

Answer 8

• Acidosis can occur with inflammation at a wound, and partly reduces the action of local anaesthetics
• Acidosis can occur with inflammation at a wound, and partly reduces the action of local anaesthetics

Question 9

Describe vasoconstrictors

Answer 9

Restrict the diffusion of the local anaesthetic away from the site of injection and thus allows the local anaesthetic to stay at the site longer, producing a longer duration of action