Principles and Pharmacology of Anaesthetics

Question 1

What are the three main kinds of anaesthetic?

Answer 1

General
Regional
Local

Question 2

What are the characteristics of general anaesthetic?

Answer 2

Produces insensibility in the whole body
Usually with loss of consciousness
Uses centrally acting drugs such as hypnotics or anaelgesics

Question 3

What are the characteristics of regional anaesthetic?

Answer 3

Produces insensibility in an area or region of the body Involves application of local anaesthetic to nerves supplying the relevant area

Question 4

What are the characteristics of local anaesthetic?

Answer 4

Produces insensibility in only the relevant part of the body

Involves application of local anaesthetic directly to the tissue.

Question 5

What is the triad of anaesthetic?

Answer 5

Analgesia
Hypnosis
Relaxation

Question 6

What aspects of the triad of anaesthetic do opiates act on?

Answer 6

Analgesia and hypnosis

Question 7

What aspects of the triad of anaesthetic do local anaesthetics act on?

Answer 7

Analgesia and relaxation

Question 8

What aspects of the triad of anaesthetic do muscle relaxants act on?

Answer 8

Relaxation

Question 9

What aspects of the triad of anaesthetic do general anaesthetic agents act on?

Answer 9

Hypnosis and relaxation

Analgesia to a lesser degree

Question 10

What is balanced anaesthesia?

Answer 10

Balanced anaesthesia involves using multiple drugs, each with altering functions. This allows a degree of control over the individual components of anaesthesia and helps keep the dosage of individual drugs down

Question 11

What are the problems with balanced anaesthesia?

Answer 11

• Increased risk of drug interactions due to polypharmacy
• Muscle relaxation- requires airway maintenance
• Separation of relaxation and hypnosis- awareness possible

Question 12

What is the physiology of general anaesthetic?

Answer 12

General anaesthetic agents interfere with neuronal ion channels, hyperpolarising them and making them less likely to fire

Question 13

What is the difference in physiology between inhalational and intravenous anaesthetic agents?

Answer 13

Inhalational agents dissolve in the membranes and have a direct physical effect
Intravenous agents act via allosteric binding to GABA receptors, opening the chloride channels

Question 14

What additional management must be given with general anaesthetic?

Answer 14

Airway management vital

Care should be taken to reduce cardiopulmonary impact

Question 15

How does the uptake of intravenous anaesthetic vary in different body tissues?

Answer 15

Initially the blood level is very high but falls as the drug moves into highly perfused tissues
Muscle picks up the drug more slowly but the effect is large because of the relative mass of skeletal muscle in the body
Fatty tissue picks up drug even more slowly but can store large amounts due to the high fat solubility of these drugs

Question 16

What is the benefit of using a target-controlled infusion pump?

Answer 16

It allows for very accurate concentrations of anaesthetic to be delivered to the blood and brain

Question 17

How do inhalational anaesthetics work?

Answer 17

Halogenated hydrocarbons taken up and excreted by the lungs

Concentration gradient where lungs > blood > brain

Question 18

What is the minimum alveolar concentration in terms of anaesthetic?

Answer 18

A measure of potency

A low concentration corresponds to a high potency

Question 19

How is inhaled anaesthetic reversed?

Answer 19

Inhalational administration is stopped so the concentration gradient is reversed

Question 20

What physiological changes occur with the administration of general anaesthetic?

Answer 20

• Depress cardiovascular centre (reduce sympathetic outflow, negative inotropic effect on heart, vasodilation)
• Direct vasodilation and venodilation
• Respiratory depressant (reduced hypoxic and hypercarbic drive, decrease tidal volume and increase rate, paralyse cilia)
• Decreases functional residual capacity

Question 21

What are the indications for muscle relaxants?

Answer 21

• Ventilation & Intubation
• When immobility is essential (microscopic surgery, neurosurgery)
• Body cavity surgery (access)

Question 22

What are the problems with muscle relaxants?

Answer 22

• Awareness
• Incomplete reversal
• Apnoea
• Relax skeletal muscle indiscriminately and so respiratory and airway muscles are also affected

Question 23

For what reasons can intraoperative analgesia be given?

Answer 23

• Prevention of arousal
• Opiates contribute to hypnotic effect of GA
• Suppression of reflex responses to painful stimuli (e.g. tachycardia , hypertension)

Question 24

What are the characteristics of local and regional anaesthetic?

Answer 24

• Retain awareness / consciousness
• Lack of global effects of GA
• Derangement of CVS physiology- proportional to size of anaesthetised area
• Relative sparing of respiratory function