PHARMACOLOGY - Anaesthetics

Question 1

What are some of the commonly used injectable anaesthetic agents?

Answer 1

Propofol
Alfaxalone
Ketamine

Question 2

What is the mechanism of action for propofol?

Answer 2

Propofol potentiates the activity of inhibitory GABAa receptors

Question 3

Which species’ is propofol liscenced in?

Answer 3

Dogs
Cats

Question 4

How should propofol be administered?

Answer 4

Intravenous (IV) administration

Question 5

Why is it recommended not to infuse propofol for more than 30 minutes?

Answer 5

Propofol is formulated with benzyl alcohol and infusion of propofol for more than 30 minutes increases the risk of benzyl alcohol toxicity

Question 6

What else can be done to reduce the risk of benzyl alcohol toxicity?

Answer 6

To reduce the risk of benzyl alcohol toxicity, don’t administer more than 24mg/kg of propofol per anaesthetic

Question 7

Why does propofol have such a rapid onset and a quick duration of action?

Answer 7

Propofol has a high lipid solubility and thus travels rapidly to the brain to carry out the desired effects. However, propofol is also rapidly redistributed to other blood rich organs and lipid stores where the drug will accumulate. Propofol is also rapidly metabolised

Question 8

Which organs metabolise propofol?

Answer 8

Liver
Unknown site

Question 9

What are the effects of propofol on the central nervous system (CNS)?

Answer 9

Rapid loss of consiousness
Anti-epileptic

Question 10

What are the effects and side effects of propofol?

Answer 10

Rapid loss of consiousness
Antiepileptic
Transient hypotension
Post-induction apnoea
Occasional muscle twitching
Heinz body anaemia in cats
Pain on injection

Question 11

What are the indicators for propofol?

Answer 11

IV induction of anaesthesia
Refractory seizures

Question 12

Why should you be cautious when using propofol in hypovolaemic patients?

Answer 12

Propofol is highly plasma protein bound and since hypovolaemic patients have fewer plasma proteins, there will be more free drug within the circulation and thus there will be a more profound pharmacological effect. Furthermore, propofol can cause vasodilation and hypotension, which will have a more profound effect in hypovolaemic patients

Question 13

Why should you be cautious when using propofol in cats with hepatic dysfunction?

Answer 13

Cats metabolise propofol slower than dogs which can result in the increased accumulation of propofol in the body, especially in cats with hepatic dysfunction who cannot metabolise the drug as effectively as a healthy animal

Question 14

Why should you be cautious when using propofol in cats that require repeat anaesthetics?

Answer 14

There is an increased risk of heinz body anaemia in cats with repeated or continuous infusions of propofol

Question 15

What is the mechanism of action for alfaxalone?

Answer 15

Alfaxalone potentiates the activity of inhibitory GABAa receptors

Question 16

Which species’ is alfaxalone liscenced in?

Answer 16

Dogs
Cats
Rabbits

Question 17

How can alfaxalone be administered?

Answer 17

Intravenous (I.V.) preferably
Intramuscular (I.M.)
Subcutaneous (S.C.)

Question 18

Why does alfaxalone have such a rapid onset and a quick duration of action?

Answer 18

Alfaxalone has a high lipid solubility and thus travels rapidly to the brain to carry out the desired effects. However, alfaxalone is also rapidly redistributed to other blood rich organs and lipid stores where the drug will accumulate. Alfaxalone is also rapidly metabolised

Question 19

Which organ metabolises alfaxalone?

Answer 19

Liver

Question 20

Why is alfaxalone tolerated better in cats compared to propofol?

Answer 20

While alfaxalone is metabolised slower in cats compared to dogs, it is not as significant as with propofol and thus there is less accumulation of alfaxalone in the body and thus it is more well tolerated in cats compared to propofol

Question 21

(T/F) Alfaxalone has higher plasma protein binding than propofol

Answer 21

FALSE. Alfaxalone has a lower plasma protein binding than propofol

Could be a better choice for induction of hypovolaemic patients

Question 22

What are the effects and side effects of alfaxalone?

Answer 22

Rapid loss of consiousness
Mild hypotension
Post-induction apnoea
Poor quality anaesthetic recovery

Question 23

What are the indicators for alfaxalone?

Answer 23

Intravenous administration to induce anaesthesia
Intravenous administration to maintain anaesthesia
Occasionally IM/SC administration for sedation

Question 24

When can IM/SC alfaxalone be benefical as a sedative?

Answer 24

IM/SC alfaxalone can be useful to sedate old/sick cats which are difficult to handle. Alfaxolone has less of a significant cardiovascular effect as other sedatives which is useful in sick animals and provides a level of sedation which is beneficial in animals that are difficult to handle

Question 25

What are the drawbacks for using IM/SC alfaxalone for sedation?

Answer 25

Not authorised Requires a large volume of alfaxalone for injection

Question 26

What is the mechanism of action for ketamine?

Answer 26

Ketamine is a glutamate-gated NMDA receptor antagonist

Question 27

Ketamine is a dissociative anaesthetic. What are the five features of dissociative anaesthesia?

Answer 27

Eyes remain open Active reflexes Hypertonicity Analgesia Decreased cardiovascular and respiratory depression

Question 28

Which species' is ketamine liscenced in?

Answer 28

Dogs Cats Horses Sheep Goats Small mammals

Question 29

How can ketamine be administered?

Answer 29

Intravenous (I.V.) Intramuscular (I.M.) Subcutaneous (S.C.)

Question 30

Which organ metabolises ketamine?

Answer 30

Liver

Question 31

What are the effects and side effects of ketamine?

Answer 31

Loss of consiousness Analgesia Proconvulsant Emergence delirium Hypertonicity Increases sympathetic tone *(tachycardia, increased CO and vasoconstriction)*

Question 32

In which two species does ketamine act as a proconvulsant?

Answer 32

Dogs Horses

Question 33

What are the effects of ketamine on the cardiovascular system?

Answer 33

Ketamine results in an increased sympathetic drive which results in an increased heart rate, cardiac contractility, cardiac output and blood pressure

Question 34

What are the effects of ketamine on the respiratory system?

Answer 34

Transient apneoa following intravenous (I.V.) administration

Question 35

What is the effect of ketamine on the musculoskeletal system?

Answer 35

Hypertonicity

Question 36

(T/F) Ketamine should **never** be used as a sole anaesthetic agent

Answer 36

TRUE.

Question 37

What are the indicators for the use of ketamine?

Answer 37

Intravenous induction of anaesthesia Intramuscular induction and maintenance of anaesthesia Provide analgesia

Question 38

What drug is ketamine combined with for IV induction of anaesthesia? | Can be done in dogs, cats and horses

Answer 38

Benzodiazepines

Question 39

Which drug is ketamine combined with for IM induction and maintenance of anaesthesia? | Can be done in dogs and cats

Answer 39

α2 agonist and opioid

Question 40

When is ketamine indicated as an analgesic drug?

Answer 40

Pre-existing pain In situations predisposed to developing chronic pain Adjunct to other analgesics for difficult to manage pain

Question 41

When may you choose ketamine as your anaesthetic agent over propofol or alfaxalone?

Answer 41

Haemodynamically unstable patients If IM anaesthesia is required

Question 42

When should you be cautious when using ketamine?

Answer 42

In patients with a history of seizures In patients with an elevated intracranial pressure (ICP) In patients with pre-existing tachycardia

Question 43

What is total intravenous anaesthesia (TIVA)?

Answer 43

Total intravenous anaesthesia (TIVA) is the use of intravenous anaesthetic agents for both induction and maintenance of anaesthesia

Question 44

Which intravenous anaesthetic drugs are appropriate for total intravenous anaesthesia (TIVA) in dogs?

Answer 44

Propofol Alfaxalone

Question 45

Which intravenous anaesthetic drug is appropriate for total intravenous anaesthesia (TIVA) in cats?

Answer 45

Alfaxalone

Question 46

What is the main advantage of using inhalational general anaesthetics as maintenance drugs?

Answer 46

Allows for rapid adjustment of anaesthetic depth

Question 47

What are the two disadvantages of using inhalational general anaesthetics as maintenance drugs?

Answer 47

There is a lot of equipment required Environmental pollution

Question 48

What is indicated by a high oil:gas partition coefficient?

Answer 48

A high oil:gas partition coefficient indicates that an inhalational anaesthetic has a higher lipid solubility and thus a higher potency (lower quantity of drug is required to achieve the desired effect)

Question 49

What is indicated by a low blood:gas partition coefficient?

Answer 49

A low blood:gas partition coefficient indicates that an inhalational anaesthetic has a more rapid induction, recovery and rate of change of anaesthetic depth

Question 50

What is the minimum alveolar concentration (MAC)?

Answer 50

The concentration of the drug required so 50% of patients will not respond to a particular stimulus

Question 51

What is indicated by a low minimum alveolar concentration (MAC)?

Answer 51

A low minimum alveolar concentration (MAC) indicates that the inhalational anaesthetic has a higher potency as a lower concentration is required to produce the desired effect

Question 52

Which organ metabolises inhalational general anaesthetics?

Answer 52

Liver

Question 53

How are inhalational general anaesthetics eliminated?

Answer 53

Expiration

Question 54

What is the risk of more highly metabolised general anaesthetics?

Answer 54

General anaesthetics are metabolised into toxic metabolites which can be eliminated through expiration and thus pose a risk to the staff in the operating theatre

Question 55

Give two examples of halogenated inhalational anaesthetic drugs

Answer 55

Isoflurane Sevoflurane

Question 56

What is the effect of isoflurane and sevoflurane on the central nervous system (CNS)?

Answer 56

Loss of consiousness

Question 57

What is the effect of isoflurane and sevoflurane on the cardiovascular system?

Answer 57

Vasodilation and hypotension

Question 58

What is the effect of isoflurane and sevoflurane on the respiratory system?

Answer 58

Respiratory depression | Less respiratory depression with sevoflurane compared to isoflurane

Question 59

Compare the phamacokinetic properties of isoflurane and sevoflurane

Answer 59

- Sevoflurane has a lower oil:gas partition coefficient and thus a higher MAC value compared to isoflurane meaning sevoflurane is **less potent** than isoflurane - Sevoflurane has a lower blood:gas partition coefficient than isoflurane so sevoflurane has a **more rapid induction, recovery and rate of change of anaesthetic depth** compared to isoflurane - Sevoflurane is more **highly metabolised** than isoflurane so they is a higher risk of the expiration of toxic metabolites

Question 60

Why is isoflurane not an appropriate induction drug?

Answer 60

Isofluorane has an unpleasant odour which will cause animals to resist the mask induction

Question 61

Why is sevofluorane an appropriate induction drug?

Answer 61

Sevofluorane has a pleasant odour, causes minimal airway irritation and has a rapid onset

Question 62

How does sevoflurane interact with CO2 absorbents?

Answer 62

Sevoflurane interacts with CO2 absorbents to generate Compound A which has been shown to cause renal injury in laboratory rodents

Question 63

What are the three factors which increase the risk of Compound A formation?

Answer 63

CO2 absorbents containing strong bases Long duration of sevoflurane exposure Low fresh gas flow