CAL: Sedation, Premedication and Induction of Anaesthesia

Question 1

Which premedication would be unsuitable for the sedation of an animal with an unstable cardiovascular system?

Answer 1

Alpha-2 agonists (medetomidine, dexmedetomidine etc. and Acepromazine

• Alpha-2 agonists: increase in BP, decreased HR (and so decreased CO)
• Acepromazine: vasodilation/hypotension, syncope, anti-arrhythmic effects

Question 2

What is a concern when administering ketamine in equine anaesthesia?

Answer 2

The potential for excitatory reactions while administering ketamine -* it is important horse has reached adequate depth of sedation prior to inducing general anaesthesia with ketamine*

• alpha 2 agonists provide reliable sedation in horses and can be used prior to anaesthetic induction.
• Butorphanol provides some analgesia and is often used for this purpose
• e.g. appropriate premedication protocol: Xylazine and butorphanol or Acepromazine and xylazine

Question 3

How should propofol be administered to induce anaesthesia?

Answer 3

• Must be intraveously
• Slowly to effect

Question 4

Propofol has a rapid onset of action.
True/false?

Answer 4

True

Question 5

Propofol provides good analgesia.
True/false?

Answer 5

False
* Analgesia must be provided for painful / surgical procedures by other means

Question 6

Propofol is good for muscle relaxation.
True/false?

Answer 6

True

Question 7

Which induction agent causes irritation and necrosis if injected extravascularly?
What action should you take in this instance?

Answer 7

Thiopentone
Flush the area with sterile saline (will dilute thiopentone) and lidocaine (may cause local vasodilation to increase uptake of the drug out of the subcutaneous tissues)

Question 8

Does propofol have a long or short duration of action?

Answer 8

Rapid onset and short duration of action

Question 9

What is the common cardiovascular side effect of the following induction agents: propofol, alfaxalone and isoflurane

Answer 9

Decreased blood pressure

Question 10

Why could mask induction with isoflurane be stressful for an animal?

Answer 10

• Causes irritation of respiratory tract
• May cause struggling and breath-holding, can result in the release of adrenaline
• Also increases the risk of arrhythmias

Question 11

What methods can be used to reduce the dose of induction agent required in a patient with cardiovascular disease?

Answer 11

1. Use premedication: drugs such as opioids provide analgesia, but they also produce good sedation with minimal cardiovascular side effects
should be cautious about using medetomidine: although it provides profound sedation and reduces the dose of induction agent required, it also has profound adverse cardiovascular effects
ACP is fine to use in some types of cardiovascular disease but should be avoided in others
2. Use a co-induction technique, combining your induction agent with a benzodiazepine (diazepam or midazolam)
Benzodiazepines can cause excitement if administered alone as a pre-med in healthy patients but this problem is minimised if they are used at the time of induction - only reduce the dose of induction agent required, do not reduce the CVS effects of induction agent
3. Administering the induction agent slowly to effect (rather than giving a rapid bolus) will also often reduce the dose which is required for induction

Question 12

Which inhalation agents could be used for a box induction in a cat?

Answer 12

1. Sevoflurane
2. Isoflurane

Sevoflurane has lower blood:gas solubility than isoflurane meaning faster speed of induction, and less irritant to respiratory tract so may cause less breath holding and secretions

Question 13

How would you carry out a box induction in a cat?

Answer 13

1. Ensure quiet environment
2. Put the patient inside box
3. De-nitrogenate the box by filling in with 100% oxygen for 5-10 minutes
4. Start inhalation agent
5. Observe the cat in the box
6. Watch for excitement phase
7. Watch for relaxed phase - must intervene and reposition if cat in abnormal position e.g. flexed neck
8. Watch breathing - should initially be rapid rate and then slower
9. Flush box with 100% oxygen to remove isoflurane
10. Open box to take cat out, intubate trachea and maintain the can on inhalation agent and oxygen

Question 14

An option for induction of anaesthesia of an aggressive cat (alternative to box method) would be a triple combination injection IM with ketamine, medetomine and methadone.
How would the monitoring of this cat look different to a cat anaesthetised with propofol?

Answer 14

Ketamine preserves CNS reflexes to a greater extent and the cat may swallow, salivate and may have an active palpebral reflex.
Jaw tone is likely to be greater than after propofol or isoflurane.
Ketamine also stimulates the sympathetic nervous system so the heart rate and blood pressure may be higher than you might expect in an animal anaesthetised with propofol or isoflurane.

Question 15

Which anaesthetic agent is not suitable for induction of anaesthesia in a cat several days in a row?

Answer 15

Propofol
* Cats have difficulty metabolising both the phenol and the lipids in propofol
* Repeated doses in a short period of time can lead to drug accumulation
* Some studies have reported slow recoveries and toxic effects such as anorexia, diarrhoea and anaemia with repeated use of propofol in cats.