Introduction to anaesthetic lectures

Question 1

What is the maximum recommended safe dose of bupivacaine?

Answer 1

2mg/kg

Question 2

What is the maximum recommended safe dose of lignocaine?

Answer 2

3mg/kg

Question 3

What is the maximum recommended safe dose of prilocaine?

Answer 3

6mg/kg

Question 4

What is meant by combination anaesthesia?

Answer 4

This is using a combination of drugs to achieve the desired effects:
Analgesia to reduce consciousness
Anaesthetic to reduce pain
Muscle relaxant to reduce muscle activity

Question 5

Why is single agent analgesia problematic?

Answer 5

It typically requires large doses of a single agent which increases the risk of toxicity

Can lead to respiratory or cardiac depression

Question 6

What are some key differences between anaesthesia and sleep?

Answer 6

Anesthesia don’t respond to pain
Anaesthesia don’t support your own airway
Anaesthesia don’t remove respiratory secretions, reduced swallowing
Don’t dream under analgesia
Analgesia you don’t move

Question 7

How can general anaesthesia be induced?

Answer 7

IV or inhalational agent

Propofol is most commonly used

Question 8

How is general anaesthesia maintained?

Answer 8

IV or inhalational agents

Question 9

What are general anaesthetic agents often combined with?

Answer 9

Analgesia- typically opioid
Muscle relaxant- e.g. suxamethonium

Or they may be combined with a local anaesthetic

Question 10

How does general anaesthesia differ from local anaesthesia?

Answer 10

Local anaesthetics prevent pain signals being generated at their source

General anaesthetics don’t prevent the pain signal being generated but reduce the central perception of pain

Question 11

How do local anaesthetic agents work?

Answer 11

They exist in an ionised and non-ionised form. The non-ionised form is able to cross the cell membranes of neurons and the ionised form them blocks the voltage dependent sodium channels- preventing AP generation

Question 12

Why is the use of LAs pH dependent?

Answer 12

The pH alters the proportion of ionised to un-ionised. There is a greater proportion of ionised LA in inflamed acidic tissue and this reduces the number of LA molecules that can cross the cell membrane, thereby reducing their effect.

Question 13

What are the two types of bonds seen in LA agents?

Answer 13

Ester or Amide

Question 14

Why does more pain result in greater LA effect?

Answer 14

The ionised form of the LA blocks the voltage gated sodium channels

There is greater opening of the sodium channels with greater pain signals and so greater blockage

Question 15

Why don’t LA agents generally block motor fibres?

Answer 15

Motor fibres are much larger in diameter and are relatively resistant to the effects of LAs

Pain fibres are smaller in diameter and so are more prone the effects of LA.

Question 16

What are some side effects of LAs?

Answer 16

Side effects develop with increasing plasma concentration

Lightheadedness, Tinnitus, Tongue numbness
Visual disturbance
Twitching
Convulsions
Unconsciousness
Coma
Respiratory arrest
Arrhythmia and CV collapse

Question 17

Name three local anaesthetic agents and give their maximum dose

Answer 17

Bupivacaine 2mg/kg
Lidocaine 3mg/kg
Prilocaine 6mg/kg

Question 18

Give some methods of local anaesthesia

Answer 18

Topical- Creams, Spray
Infiltration- Injections into the target tissue
Regional nerve block- targeting a single nerve or plexus
Epidural- Into the epidural space
Spinal- LA injected into the subarachnoid space
IV Regional- Cuff used to reduce blood flow and IV anaesthetic give, very rarely done

Question 19

What is often combined with LAs to reduce the systemic toxicity?

Answer 19

Adrenaline is used to cause vasoconstriction and reduce systemic uptake of the LA

This shouldn’t be done for toes and fingers as it could significantly reduce blood flow

Question 20

What are some side effects of spinal/epidural anaesthesia?

Answer 20

Arrhythmia
Muscle paralysis
Urinary retention
Respiratory depression

Question 21

Where is LA typically injected for an epidural?

Answer 21

Between L3 and L4

Question 22

What kind of needle is used for an epidural?

Answer 22

A touhy needle is used