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CNS > Anaesthetic agents > Flashcards

Anaesthetic agents Flashcards

1
Q

Anaesthesia is a triad of what 3 things?

A

Unconsciousness (sleep)
Muscle relaxation (immobilisation)
Analgesia

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2
Q

What injectable drugs are used to cause unconsciousness? (All GABA agonists except one - which one?)

A

Propofol
Alfaxalone (not alfoxolaner)
Ketamine - NMDA agonist
Thiopental

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3
Q

What drugs are used for maintenance of unconsciousness? (inhalation)

A

Sevoflurane

Isoflurane

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4
Q

What are the advantages of injectable induction agents of anaesthesia, cf inhalation?

A

Injectable don’t require specialised equipment, don’t pose risk to personnel
Inhalational require specialised equipment and potential environmental contamination and risk to personnel

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5
Q

What are the advantages of using inhalation agents compared to injectable?

A

Easily and quickly eliminated
Easy to adjust depth
(Injectables need metabolising and excretion, difficult to adjust depth)

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6
Q

How does propofol work? How does dose affect propofol effects?

A

GABA agonist
Low dose = sedation
High dose = anaesthesia

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7
Q

How is propofol administered? Why?

A

IV only - not lipid soluble so must be made into emulsion, can cross BBB
IM - metabolism faster than rate of uptake

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8
Q

Why should propofol not be used to top up anaesthesia?

A

Some contains preserves - accumulate and cause prolonged seizures, haemolysis and Heinz body anaemia (anaemia due to formation of Heinz bodies after haemolysis)

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9
Q

Which tissues does propofol enter?

A

Crosses BBB to cause unconsciousness

Also enters other tissues

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10
Q

How does propofol distribution cause an animal to wake up?

A

As drug distributed, levels in blood drop
Causes propofol to leave BBB down new concentration gradient
Requires more or another agent

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11
Q

Where is propofol metabolised?

A

Liver

GI

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12
Q

Which species should not be given propofol (or can be given with care)?

A

Cats

Cats struggle to metabolise propofol = accumulation and prolonged anaesthesia

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13
Q

How does propofol affect BP?

A

Causes vasodilation
Baroreceptors would usually detect this and cause increased HR
Baroreceptors blocked by propofol = drop in blood pressure

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14
Q

Propofol can cause post-induction apnea. What is this? Why dos this happen?

A

Respiratory depression due to anaesthetic

CNS thinks lower blood CO2 is normal - stimulus to breathe removed until CO2 increases

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15
Q

How does alfaxalone work?

A

GABA agonist

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16
Q

Where is alfaxalone metabolised? How can it be administered?

A 
Liver
Lipid soluble (IM, SC) but can be made water soluble (IV)
17
Q

Both alfaxalone and propofol are GABA inhibitors used for anaesthesia. They both cause vasodilation, how do they differ in terms of baroreceptors?

A

Propofol - blocks baroreceptors, vasodilation causes decreased BP
Alfaxalone - baroreceptors intact, compensatory increase in HR causes increased blood pressure

18
Q

What are the adverse effects of alfaxalone?

A

Tachycardia (due to preserved baroreflex)
Excitable recoveries
Respiratory depression

19
Q

Why is alfaxalone often the agent of choice in cats?

A

Doesn’t accumulate

Doesn’t cause Heinz body anaemia

20
Q

How does NMDA work? It causes dissociative anaesthesia. What does this mean?

A

NMDA antagonist

Disconnects higher brain functions from body

21
Q

Where is ketamine metabolised ? What is metabolised to? Which species is the exception?

A

Metabolised - liver (into nor-ketamine, less potent but can prolong anaesthetic)
Cats - not metabolised, excreted unchanged in urine

22
Q

What are the side effects of ketamine?

A

Analgesia (good)
Direct myocardial depression
Respiratory depression
Muscle hypertonicity

23
Q

Why may animals still be able to swallow and blink under ketamine anaesthesia?

A

Ketamine maintains cranial nerve reflexes

24
Q

How does thiopental work? When is it used?

A

GABA agonist

Equine only

25
Q

How is thiopental adminsitered? How is it metabolised?

A

IV only as irritant

Slow hepatic metabolism - accumulates if repeated dose

26
Q

What are the adverse effects of thiopental?

A

Respiratory depressio
Myocardial depression
Increased incidence of arrhythmias

27
Q

Inhalational agents are used for maintaining anaesthesia. Can they be used for induction?

A

Yes but dangeous

28
Q

What is the minimum alveolar concentration? (MAC)

A

Concentration at which 50% of patients will not respond to noxious stimuli

29
Q

What is MAC expressed as? Describe its relationship with potency

A

% of atmospheric pressure

As MAC increases, potency decreases

30
Q

If not using other drugs (rare), what multiple of MAC should be used for surgery?

A

1.2-1.5X mac

31
Q

How do premedication agents, opioids and induction agents affect the MAC and amount of inhalation agents needed?

A

Other drugs decrease MAC and amount of other drugs needed

32
Q

What is the alveolar concentration?

A

% of inhalation agent in alveoli

33
Q

Inhalational agents are taken from the alveoli into the blood and to the brain. Not all of the agent is active - some is dissolved in the blood. What type of the drug (dissolved or undissolved) has anaesthetic effect?

A

Undissolved has anaesthetic effect - NOT dissolved

34
Q

What affects the amount of drug that dissolves? How does this affect amount of drug needed?

A

Solubility

More soluble- more dissolves - more needed to have an effect

35
Q

How do less soluble agents allow a faster wake up?

A

Less soluble - more likely to go from the blood stream and to the lungs to be exhaled

36
Q

What are adverse effects of isoflurane and sevoflurane?

A

Cause vasodilation

Cause respiratory depression

37
Q

Is respiratory depression more of an issue with sevoflurane or isoflurane? Why?

A

Isoflurane - more pungent, breathed easily

Sevoflurane not breathed as easily - less respiratory depression

38
Q

Isoflurane causes more respiratory depression than sevoflurane. Why is isoflurane still commonly used?

A

Cheaper

Low MAC - requires less - even cheaper

CNS (15 decks)

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