Principles and Pharmacology

Question 1

How do general anaesthetics work?

Answer 1

• Produces insensibility in the whole body and complete lack of awareness
• Centrally acting drugs (hypnotics/analgesics)

Question 2

How do regional anaesthetics work?

Answer 2

• Produce insensibility in an area or region of the body
• Local anaesthetics are applied to nerves supplying the area of the body that requires anaesthetising, e.g. brachial plexus or pedundal nerve block

Question 3

How do local anaesthetics work?

Answer 3

• Produce insensibility in only the relevant area of the body
• Local anaesthetics applied directly to the relevant tissues
• Block Na+ channels and prevent axonal AP from propagating

Question 4

What is the triad of anaesthesia?

Answer 4

1 - Hypnosis (sleepiness, unconsciousness)

2 - Analgesia (opiates or local anaesthetics)

3 - Relaxation (ONLY skeletal muscle)

Question 5

Which drugs/types of anaesthetics contribute to each of the 3 factors of anaesthesia?

Answer 5

Analgesia - Local anaesthetics, general anaesthetics, opiates

Hypnosis - General anaesthetics, opiates

Relaxation - Local anaesthetics, general anaesthetics, muscle relaxants

Question 6

Do each of the 3 factors of anaesthesia contribute equally in each type of anaesthesia (general, local, regional)?

Answer 6

No

Local anaesthetics - analgesia ONLY

Spinal anaesthetic - analgesia and relaxation ONLY

Question 7

What is the concept of balanced anaesthesia?

Answer 7

• Different drugs do different jobs
• The doses of each anaesthetic drug are titrated separately and therefore more accurate to the requirements
• Avoid overdoses
• Greater flexibility (each component of the triad can be controlled individually)

Question 8

What reflexes are spared in general anaesthesia?

Answer 8

Spinal reflexes and automatic functions

Question 9

What are the benefits of providing anaesthesia intravenously?

Answer 9

1 - Rapid onset of unconsciousness

2 - Rapid recovery

Question 10

How does the concentration of anaesthetic agents change over time following a bolus dose in each of the following body compartments?

1 - Blood + vessel rich organs

2 - Viscera

3 - Muscle

4 - Fat

Answer 10

Blood + vessel rich organs:

• Initially very high concentrations
• Gradually decreases as the drug moves into highly perfused tissues

Viscera:

• Concentration builds up quickly then gradually decreases

Muscle:

• Concentration builds up slowly
• Effect of drug on muscle is large due to the relative mass of muscle in the body

Fat:

• Concentration build-up is the slowest out of all the tissues
• Large amounts of the drug can be stored in fatty tissue due to the fat-solubility of the anaesthetic drugs

Question 11

How are inhalational anaesthetics taken up and excreted by the body?

Answer 11

• Uptake and excretion via the lungs
• Drugs pass through lungs > blood > brain

Question 12

What type of subtance are inhalational anaesthetics?

Answer 12

Halogenated hydrocarbons

Question 13

What is minimum alveolar concentration and how does it relate to potency of inhalational anaesthetics?

Answer 13

Minimum alveolar concentration (MAC) = A measure of potency of the anaesthetic drug and describes the concentration of the drug required in the alveoli required to produce anaesthesia.

Low MAC number = High potency

Question 14

What is the most common sequence of general anaesthesia?

Answer 14

1 - IV induction

2 - Inhalational maintenance

Question 15

What is an example of an IV anaesthetic?

Answer 15

Propofol

Question 16

What are the physiological changes to the cardiovascular system during General Anesthesia?

Answer 16

Reduces sympathetic outflow

Negative inotropic/chronotropic effect on heart

Reduced cardiac output

Arterial vasodilation

Decreased peripheral resistance

Decreased venous return

Question 17

What are the physiological changes to the respiratory system during General Anesthesia?

Answer 17

Depression of the respiratory system via depressing the brainstem respiratory centres:

• Reduced hypoxic and hypercarbic drive
• Reduced tidal volume
• Increase respiratory rate

Question 18

What is the most important effect that general anaesthesia has on the respiratory system?

Answer 18

It reduces lung volumes

Question 19

On which type of muscle do muscle relaxants work?

Answer 19

Skeletal muscle (including respiratory and airway muscles)

Question 20

What are the indications for muscle relaxants?

Answer 20

1 - Ventilation & intubation

2 - When immobility is essential

3 - Body cavity surgery

Question 21

What are some of the problems associated with muscle relaxants?

Answer 21

1 - Being aware

2 - Incomplete reversal

3 - Failure to maintain the airway will result in death

Question 22

Why are analgesics given to unconscious patients during surgery?

Answer 22

• Prevent arousal
• Opiates contribute to hypnotic effect of GA
• Suppress reflex response to painful stimulii (e.g. tachycardia, hypertension)

Question 23

How does regional anaesthesia affect physiology?

Answer 23

• Mainly CVS
• Respiratory function is largely preserved

Question 24

What happens to ion channels during general anaesthesia?

Answer 24

hyperpolarised and are therefore less likely to ‘fire’

Question 25

How do inhaled general anaesthetic agents work?

Answer 25

Dissolve in membranes therefore provide a direct physical effect

Question 26

Which receptors and ion channels are affected by IV general anaesthesia?

Answer 26

GABA receptors

Chloride ion channels