General Anaesthesia

Question 1

What is general anaesthesia?

Answer 1

• Reversible, drug induced loss of consciousness, usually to allow a surgical procedure to be performed

Question 2

What is the difference between local and general anaesthesia?

Answer 2

• Local is only one portion of the body

* general is the whole body

Question 3

Name 4 Inhalation anaesthetic agents

Answer 3

• Nitrous oxide
• Isoflurane
• Sevoflurane
• Desflurane

Question 4

What is etonox, when is it used?

Answer 4

• 50:50 nitrous oxide: oxygen

* Analgesic used in labour and trauma

Question 5

What is the relationship between potency and lipid solubility?

Answer 5

• The more lipid soluble an agent is, the more potent it is

Question 6

What is the MAC?

Answer 6

The minimum alveolar concentration at which 50% of the population fail to respond to surgical stimulus, the higher the MAC, the lower the potency

Question 7

What is the relationship between onset and blood solubility

Answer 7

The more blood soluble an agent is, the slower the onset

Question 8

Describe the GABA A receptor

Answer 8

• Pentameric arrangement
• Central ion channel pore
• 18 possible subunits

Question 9

What are intravenous anaesthetics mediated by?

Answer 9

• The beta subunit of the GABA a receptor

* The beta 2 subunit mediates IV hangover

Question 10

At therapeutic doses, where is the main site of action of general anaesthetics?

Answer 10

• Main is the thalamus

* Also reticular formation, brain stem and spinal cord

Question 11

Describe waking up from general anaesthesia

Answer 11

• Administration and elimination can only occur from the central compartment
• Waking up tends to happen with re-distribution and falling concentration in the Brain

Question 12

What are the effects of general anaesthesia on the CNS?

Answer 12

• Negative inotropic effect on the heart
• Will reduce systemic vascular resistance
- be careful in those with shock
- ketamine is the exception - it can cause tachycardia
• Any drug causing a loss of consciousness may lead to obstruction
- fall in resp rate with IV
- fall in tidal volume with inhalation agents (ketamine is the exception)

Question 13

What are the properties of an ideal anaesthetic?

Answer 13

• Act rapidly
• pleasant
• Cheap
• Stable
• Analgesic effect
• amnesic effect
• Minimal hangover

Question 14

What are the properties that you would not want from an anaesthetic?

Answer 14

• Irritant on veins or airways
• Emetic
• Minimal effects on other systems

Question 15

When selecting an anaesthetic, what should you bear in mind?

Answer 15

• Health and requests of patient
• Properties of the drugs
• Requirements of surgery e.g. is a muscle relaxant required

Question 16

What are three commonly used IV anaesthetics?

Answer 16

• Propofol
• Thiopentone
• Etomidate

Question 17

BP and IV anaesthetics

Answer 17

• Thiopentone reduces BP slightly
• Propofol reduces BP
• Ketamine increases BP slightly
• Etomidate nada

Question 18

Cardiac output and IV anaesthetics

Answer 18

• Thiopentone reduces cardiac output slightly
• Propofol decreases cardiac output
• Ketamine increases cardiac output slightly
• Etomidate no effect

Question 19

ICP and IV anaesthetics

Answer 19

• Thiopentone decreases ICP
• Propofol decreases ICP
• Ketamine increases ICP

Question 20

Which anaesthetics are painful on injection?

Answer 20

• Propofol

* Etomidate

Question 21

What is the overton Meyer hypothesis?

Answer 21

Correlation between lipid solubility and potency