PHARMACOLOGY - Anaesthetics Flashcards
Give three examples of injectable anaesthetic agents
Propofol
Alfaxalone
Ketamine
What is the mechanism of action for propofol?
Propofol potentiates the activity of inhibitory GABAa receptors
Which species’ is propofol liscenced in?
Dogs
Cats
How should propofol be administered?
Intravenous (I.V.)
Why is it recommended not to infuse propofol for more than 30 minutes?
Propofol is formulated with benzyl alcohol and infusion of propofol for more than 30 minutes increases the risk of benzyl alcohol toxicity
What else can be done to reduce the risk of benzyl alcohol toxicity?
To reduce the risk of benzyl alcohol toxicity, don’t administer more than 24mg/kg of propofol per anaesthetic
Why does propofol have such a rapid onset and a quick duration of action?
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
Which organs metabolise propofol?
Liver
Unknown site
What are the effects of propofol on the central nervous system (CNS)?
Rapid loss of consiousness
Anti-epileptic
What are the five side effects of propofol?
Transient hypotension
Post-induction apnoea
Occasional muscle twitching
Heinz body anaemia in cats
Pain on injection
What are the two main indicators for the use of propofol?
Intravenous induction of anaesthesia
Management of refractory seizures
Why should you be cautious when using propofol in hypovolaemic patients?
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
Why should you be cautious when using propofol in cats with hepatic dysfunction?
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
Why should you be cautious when using propofol in cats that require repeat anaesthetics?
There is an increased risk of heinz body anaemia in cats with repeated or continuous infusions of propofol
What is the mechanism of action for alfaxalone?
Alfaxalone potentiates the activity of inhibitory GABAa receptors
Which species’ is alfaxalone liscenced in?
Dogs
Cats
Rabbits
How can alfaxalone be administered?
Intravenous (I.V.) preferably
Intramuscular (I.M.)
Subcutaneous (S.C.)
Why does alfaxalone have such a rapid onset and a quick duration of action?
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
Which organ metabolises alfaxalone?
Liver
Why is alfaxalone tolerated better in cats compared to propofol?
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
(T/F) Alfaxalone has higher plasma protein binding than propofol
FALSE. Alfaxalone has a lower plasma protein binding than propofol
Could be a better choice for induction of hypovolaemic patients
What is the effect of alfaxalone on the central nervous system (CNS)?
Rapid loss of consiousness
What are the two side effects of alfaxalone?
Mild hypotension
Post-induction apnoea
What are some of the other effects of alfaxalone?
Alfaxalone can result in a poor quality anaesthetic recovery especially if there has been limited premedication
What are the three main indicators for the use of alfaxalone?
Intravenous administration to induce anaesthesia
Intravenous administration to maintain anaesthesia
Occasionally IM/SC administration for sedation
When can IM/SC alfaxalone be benefical as a sedative?
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
What are the drawbacks for using IM/SC alfaxalone for sedation?
Not authorised
Requires a large volume of alfaxalone for injection
What is the mechanism of action for ketamine?
Ketamine is a glutamate-gated NMDA receptor antagonist
Ketamine is a dissociative anaesthetic. What are the five features of dissociative anaesthesia?
Eyes remain open
Active reflexes
Hypertonicity
Analgesia
Decreased cardiovascular and respiratory depression
Which species’ is ketamine liscenced in?
Dogs
Cats
Horses
Sheep
Goats
Small mammals
How can ketamine be administered?
Intravenous (I.V.)
Intramuscular (I.M.)
Subcutaneous (S.C.)
Which organ metabolises ketamine?
Liver
What are the effects of ketamine on the central nervous system (CNS)?
Loss of consiousness
Analgesia
Proconvulsant
Emergence delirium
In which two species does ketamine act as a proconvulsant?
Dogs
Horses
What are the effects of ketamine on the cardiovascular system?
Ketamine results in an increased sympathetic drive which results in an increased heart rate, cardiac contractility, cardiac output and blood pressure
What are the effects of ketamine on the respiratory system?
Transient apneoa following intravenous (I.V.) administration
What is the effect of ketamine on the musculoskeletal system?
Hypertonicity
(T/F) Ketamine should never be used as a sole anaesthetic agent
TRUE.
What are the three main indicators for the use of ketamine?
Intravenous induction of anaesthesia
Intramuscular induction and maintenance of anaesthesia
Provide analgesia
What drug is ketamine combined with for IV induction of anaesthesia?
Can be done in dogs, cats and horses
Benzodiazepines
Which drug is ketamine combined with for IM induction and maintenance of anaesthesia?
Can be done in dogs and cats
α2 agonist and opioid
When is ketamine indicated as an analgesic drug?
Pre-existing pain
In situations predisposed to developing chronic pain
Adjunct to other analgesics for difficult to manage pain
When may you choose ketamine as your anaesthetic agent over propofol or alfaxalone?
Haemodynamically unstable patients
If IM anaesthesia is required
When should you be cautious when using ketamine?
In patients with a history of seizures
In patients with an elevated intracranial pressure (ICP)
In patients with pre-existing tachycardia
What is total intravenous anaesthesia (TIVA)?
Total intravenous anaesthesia (TIVA) is the use of intravenous anaesthetic agents for both induction and maintenance of anaesthesia
Which intravenous anaesthetic drugs are appropriate for total intravenous anaesthesia (TIVA) in dogs?
Propofol
Alfaxalone
Which intravenous anaesthetic drug is appropriate for total intravenous anaesthesia (TIVA) in cats?
Alfaxalone
What is the main advantage of using inhalational general anaesthetics as maintenance drugs?
Allows for rapid adjustment of anaesthetic depth
What are the two disadvantages of using inhalational general anaesthetics as maintenance drugs?
There is a lot of equipment required
Environmental pollution
What is indicated by a high oil:gas partition coefficient?
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)
What is indicated by a low blood:gas partition coefficient?
A low blood:gas partition coefficient indicates that an inhalational anaesthetic has a more rapid induction, recovery and rate of change of anaesthetic depth
What is the minimum alveolar concentration (MAC)?
The concentration of the drug required so 50% of patients will not respond to a particular stimulus
What is indicated by a low minimum alveolar concentration (MAC)?
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
Which organ metabolises inhalational general anaesthetics?
Liver
How are inhalational general anaesthetics eliminated?
Expiration
What is the risk of more highly metabolised general anaesthetics?
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
Give two examples of halogenated inhalational anaesthetic drugs
Isoflurane
Sevoflurane
What is the effect of isoflurane and sevoflurane on the central nervous system (CNS)?
Loss of consiousness
What is the effect of isoflurane and sevoflurane on the cardiovascular system?
Vasodilation and hypotension
What is the effect of isoflurane and sevoflurane on the respiratory system?
Respiratory depression
Less respiratory depression with sevoflurane compared to isoflurane
Compare the phamacokinetic properties of isoflurane and sevoflurane
- 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
Why is isoflurane not an appropriate induction drug?
Isofluorane has an unpleasant odour which will cause animals to resist the mask induction
Why is sevofluorane an appropriate induction drug?
Sevofluorane has a pleasant odour, causes minimal airway irritation and has a rapid onset
How does sevoflurane interact with CO2 absorbents?
Sevoflurane interacts with CO2 absorbents to generate Compound A which has been shown to cause renal injury in laboratory rodents
What are the three factors which increase the risk of Compound A formation?
CO2 absorbents containing strong bases
Long duration of sevoflurane exposure
Low fresh gas flow
