General Anaesthetic

Question 1

What is involved in the ‘Triad of Anaesthesia’?

Answer 1

Analgesia (lack of pain)
Narcosis (lack of memory)
Muscle Relaxation (depressed reflex responses)

Question 1

Injectable Anaesthetics
Why are they used?

Answer 1

• Induction prior to inhalation anaesthesia
• Sole agent for short duration procedures
• Suppress CNS stimulation in certain conditions

Question 2

How are injectable anaesthetic drugs distributed around the body?

Answer 2

1. Brain receives high concentration of drug after IV injection
2. Unconsciousness occurs when a critical concentration is reached in the brain
3. Over time, less well-perfused organs take up the drug
4. Results in a reduction of plasma levels which creates a diffusion gradient for drug levels to move from the brain to plasma
5. Consciousness returns as the brain drug level falls below critical

Question 3

How are GA drugs metabolised and excreted in the body?

Answer 3

Metabolised in the liver
- Converting from lipid to water soluble molecules
Excreted in bile or urine

Question 4

What is Total Intravenous Anaesthesia (TIVA)?

Answer 4

An alternative to gaseous anaesthetics.
- Avoids side effects of inhalation agents
- Useful where inhalation delivery would compromise access for surgery

Question 5

Injectable Anaesthetics
Name a Phenol Derivative Drug and its Advantages and Disadvantages.

Answer 5

Propofol

Advantages:
- Rapid metabolism and recovery
- Non irritant perivascular
- Can be used for TIVA as non-cumulative

Disadvantages:
- Apnoea if injected too fast
- Hypotension and bradycardia
- Excitable recovery

Question 6

Injectable Anaesthetics
Name a Steroid Anaesthetic Drug and its Advantages and Disadvantages.

Answer 6

Alfaxalone

Advantages:
- Rapid, smooth induction
- Minimal cardio/respiratory depression
- Rapid elimination
- No pain on injection

Disadvantages:
- Adequate premed required for smooth induction
- Excitable recovery

Question 7

Injectable Anaesthetics
Name a Dissociative Anaesthetic Drug and its Advantages and Disadvantages.

Answer 7

Ketamine

Advantages:
- Provide analgesia
- Protective airway reflexes maintained

Disadvantages:
- Poor muscle relaxation
- Slow onset of anaesthesia