General Anaesthetics

Question 1

How can general anaesthetics be administered?

Answer 1

intravenous injection or inhalation

Question 2

What three things do general anaesthetics need to achieve?

Answer 2

• need to make the patient unconscious
• need for analgesia (no pain)
• muscle relaxation (loss of reflexes)

Question 3

How do general anaesthetics work?

Answer 3

by depressing CNS activity

Question 4

What do all the inhabited anaesthetics have in common?

Answer 4

• simple, unreactive compounds
• short chain
• not one chemical class

Question 5

What happens in high pressure?

Answer 5

reverses anaesthesia

Question 6

What proves the lipid solubility case wring?

Answer 6

-as the chain length of long chain anaesthetic compound increases its lipid solubility increases however anaesthetic potency stops beyond a certain length

Question 7

What gives evidence that the protein theory might be correct?

Answer 7

stereo selectivity (one orientation of an exactly the same molecule has more anaesthetic potency than another orientation of the same molecule) this suggests protein binding

Question 8

Why is lipid solubility important?

Answer 8

to allow the molecule to enter the membrane and bound to a hydrophobic pocket on a protein

Question 9

What are the molecular targets for inhaled/gaseous general anaesthetics?

Answer 9

• ion channels but no single target
• GABA A receptor (increase inhibition)
• K+ channel activation (decrease membrane excitability)
• blocking excitatory ligand-gated channels such as NMDA and ACh nicotinic
• increase inhibition by binding to the glycine channel

Question 10

What are the stages of anaesthesia?

Answer 10

1. Analgesia (drowsiness, reflexes intact, still conscious)
2. Delirium (induction phase) (excitement, delirium, incoherence, loss of consciousness, unresponsive to painful stimuli) (also some dangerous symptoms such as muscle rigidity, spasmodic movements, cardiac arrhythmias, vomiting and choking)
3. Surgical anaesthesia (unresponsive to painful stimuli, regular breathing, abolition of reflexes, muscle relaxation)
4. Medullary paralysis (overdose) (pupillary dilation, respiration/circulation ceases, EEG wanes) (can lead to death)

Question 11

What are two key factors of an anaesthetic agent?

Answer 11

potent and fast acting

Question 12

How do you measure anaesthetic potency?

Answer 12

MAC
minimum alveolar concentration in man
(the conc of anaesthetic in the alveoli required to produce immobility in 50% of patients when exposed to noxious stimulus)

Question 13

What is MAC inversely proportional to?

Answer 13

lipid solubility

Question 14

What is the main determinant of anaesthetic potency?

Answer 14

lipid solubility

Question 15

Why is it important to have fast acting anaesthetics?

Answer 15

gets through the dangerous phases quickly

Question 16

What are the factors influencing the rate of induction?

Answer 16

• properties of anaesthetic

- physiological factors

Question 17

What are the two partition coefficients that the anaesthetic needs to get through in order to reach the brain?

Answer 17

-blood:gas partition constant
-tissue:blood partition constant
(have to reach equilibrium)

Question 18

When inhaling the anaesthetic, how can you increase the rate of conduction?

Answer 18

increase conc of anaesthetic

increase rate and depth of breathing

Question 19

In order to make anaesthesia faster do you want an anaesthetic that is highly soluble in the blood?

Answer 19

no, it has to be a bit soluble in the blood but having a high solubility means that the blood has a high capacity so more molecules are required to saturate the blood before it transfers into the brain (slow down speed of conduction)
a relatively low blood insoluble gas means capacity is smaller so saturation occurs faster so the transfer to the brain is faster

Question 20

What is blood:gas partition coefficient inversely proportional to?

Answer 20

speed of induction

Question 21

What does a faster rate of pulmonary flow mean?

Answer 21

higher cardiac output so faster transfer

Question 22

What is the solubility of anaesthetic lie in the brain?

Answer 22

conc of anaesthetic in the brain rises fast because anaesthetics are soluble in lean tissue (grey matter, muscle)

Question 23

If a patient has a lot of adipose fat, will it increase or decrease the speed of induction?

Answer 23

decrease because anaesthetics are highly soluble in adipose tissue (more soluble than in the brain)

Question 24

How does tissue blood flow affect induction?

Answer 24

high tissue blood flow eg brain increases induction

Question 25

How do you eliminate inhaled anaesthetics?

Answer 25

-mainly via the lung (speed of induction in reverse)

Question 26

Look at advantages and disadvantages of different anaesthetics

Answer 26

on slides

Question 27

What is balanced anaesthesia?

Answer 27

using combinations of different drugs for optimal clinical effect with lower risk

Question 28

What are the features of intravenous anaesthetics?

Answer 28

• rapid onset

- short acting

Question 29

When are intravenous anaesthetics used?

Answer 29

in induction

or used alone in short procedures

Question 30

How do intravenous anaesthetics work?

Answer 30

through interaction with specific ligand gates receptors e.g GABA A

Question 31

What types of premedication can you use before using an anaesthetic?

Answer 31

• benzodiazepines (sedation and amnesia)
• opioids (pain relief)
• antimuscarinics (to facilitate intubation and ventilation)

Question 32

What is a muscle relaxant used for?

Answer 32

to relax deep abdominal, tracheal and diaphragm muscles without the need for deeper anaesthesia

Question 33

What is an anti-emetic?

Answer 33

prevents the patient from throwing up as they recover