Induction Agents

Question 1

What are the induction agents used in veterinary medicine?

Answer 1

• Ketamine
• Propofol
• Alfaxalone
• Thiopentone (old barbiturate induction agent sometimes used in horses)

Question 2

Define an Induction Agent

Answer 2

The administration of a drug, or combination of drugs, at the beginning of an anesthetic that results in unconsciousness
- Typically following a pre-medication

Question 3

What are Induction agents used IV?

Answer 3

• Ketamine + Diazepam: bolus
• Propofol: slow adm
• Alfaxalone: slow adm
• Thiopentone: bolus (slow adm will result in excitement)

Question 4

What Induction agents used IM?

Answer 4

• Ketamine +/- alpha2 agonist or Diazepam (Ketamine stings though!)
• Alfaxalone: good for cats!

Question 5

Are there reversal agents for the 4 induction agents?

Answer 5

No!

Question 6

Once an animal has been induced, what must be done ?

Answer 6

• Monitor patients vitals (RR + HR)
• Intubate +/- IPPV
• Oxygen supplementation
• Emergency drugs at the ready

Question 7

What are the benefits of using Alfaxalone?

Answer 7

• Causes minimal CVS changes (ie SVR, HR and BP): good for cardiac disease patients
• Good muscle relaxation

Question 8

What are the benefits of using Ketamine?

Answer 8

• Provides dissociative analgesia at NMDA receptors

Question 9

What are the benefits of using Propofol?

Answer 9

• Rapid and Smooth recovery
• Good muscle relaxation
• Non-cumulative, suitable for TIVA
• Suitable for thin dogs and “sight” hounds
• Not arrhythmogenic
• Extra-hepatic metabolism: good for liver disease patients

Question 10

What are the benefits of using Thiopentone?

Answer 10

• Rapid (30 sec) induction, the others can take up to a minute
• Good muscle relaxation

Question 11

What are the cautions of using Alfaxalone?

Answer 11

• Post-induction apnea
• Respiratory depression, especially with repeated top-ups
• NO analgesia

Question 12

What are the cautions of using Ketamine?

Answer 12

• CVS changes: increase HR + BP (can be beneficial though)
• Post-induction apnea
• Respiratory depression, especially with repeated top-ups
• Inadequate muscle relaxation when given alone, must give with alpha2 or BZD

Question 13

What are the cautions of using Propofol?

Answer 13

• CVS changes: vasodilation + possible bradycardia and drop in BP
• Post-induction apnea: can be avoided by adm. slowly and is usually short lived (2-3 mins)
• Respiratory depression, especially with repeated top-ups
• NO analgesia
• Propofol twitches: muscle twitches are self-limiting

Question 14

What are the cautions of using Thiopentone?

Answer 14

• CVS changes: vasodilation + tachycardia
• Post-induction apnea
• Respiratory depression, especially with repeated top-ups
• Can cause heightened sense of pain if given alone
• If accidentally given peri-vascularly, it is VERY irritant and will cause sloughing of the skin. Animals with black hair will grow white hair in that area permanently

Question 15

Give an IM injectable anesthesia protocol useful for short procedures (e.g. sedation for xrays or quill removal)

Answer 15

IM: Medetomidine + Ketamine +/- Butorphanol

Question 16

Which induction agents can be used for Induction and then topped up during the procedure?

Answer 16

• Propofol
• Alfaxalone
• Ketamine + Diazepam

note: Thiopentone CANNOT be used for top ups due to its long recovery time

Question 17

What are the 2 main IV injectable protocols used in equine practice?

Answer 17

1) Alpha 2 agonist + Ketamine +/- Butorphanol (IV)
This can be topped up as required (1/3 to 1/2 of initial dose every 10 mins)

2) Triple Drip: Guaifenesin, Xylazine, Ketamine (IV)
Given CRI or Bolus top up as needed

Question 18

What is TIVA?

Answer 18

Total Intra-Venous Anesthesia
A technique of general anaesthesia using a combination of agents given solely by the intravenous route and in the absence of all inhalational agents including nitrous oxide

note: using intermittent top-ups of propofol in dogs/cats, or xylazine + ketamine top-ups in the horse is NOT considered true TIVA