Clinical Induction of Anaesthesia

Question 1

Induction of anaesthesia definition

Answer 1

the administration of a drug or combo of drugs at the beginning of an anaesthetic that results in the unconsciousness and allows you to intubate the patient

Question 2

How fast does it take for induction of anaesthesia occur?

Answer 2

Thiopentone - 20-30 secs (1 circulation time)
All other drugs - about 2 mins (4 circulation times)

Question 3

What are the methods of inducing anaesthesia?

Answer 3

• IV injection given to effect
• IM injection
• Inhalation/mask or chamber

Question 4

How long does IV injection of induction take?

Answer 4

up to 2 minutes

Question 5

How long does IM injection of induction of anaesthesia take?

Answer 5

5-30 mins

Question 6

Why is inhalation induction of anaesthesia not recommended?

Answer 6

• stressful for P
• poor for environment (world) & working environment

Question 7

What are a few things to remember about induction?

Answer 7

• IV & IM induction of anaesthesia is irreversible
• Ensure you administer the correct dose (based on body weight)
• Have a ‘Plan B’ in case of problems
• Monitor the patient’s vitals
• Be ready for intubation
• have O2 source

Question 8

What characteristics would make the ideal agent for induction of anaesthesia?

Answer 8

• has rapid onset of action
• minimum alteration to HR or BP
• minimum post-induction apnoea
• rapid & smooth recovery w/ no hangover
• provides analgesia
• provides good muscle relaxation
• minimal organ toxicity
• no venous/injection issues
• suitable physical properties

Question 9

Which drugs have a rapid onset of action (one ‘arm-to-brain’ circulation time - 30 seconds) for induction?

Answer 9

Thiopentone

Question 10

Which induction drugs have minimum alterations to HR or BP?

Answer 10

Alfaxalone
Ketamine

Question 11

Which induction agents have minimum post-induction apnoea?

Answer 11

Alfaxalone & ketamine
Propofol & Thiopentone especially

Question 12

When propofol is given too much too fast during induction, what occurs?

Answer 12

signs of an overdose = post-induction apnoea

Question 13

What induction drugs have a rapid & smooth recovery w/ no hangover?

Answer 13

Propofol

Question 14

What induction agents provide analgesia?

Answer 14

Ketamine

Question 15

What induction drugs provide good muscle relaxation?

Answer 15

Alfaxalone
Propofol
Thiopentone

Question 16

What induction drugs cause minimal organ toxicity?

Answer 16

Alfaxalone
Propofol
Ketamine
Thiopentone

Question 17

What is a caution with using propofol in cats?

Answer 17

Repeated anaesthesia can cause Heinz Body anaemia

Question 18

What induction drugs cause no venous/injection issues?

Answer 18

Alfaxalone
Ketamine
Propofol - some preparations

Question 19

What induction drugs have suitable physical properties?

Answer 19

alfaxalone
Ketamine
Thiopentone

Question 20

What is marketed as the gold standard medication of induction of anaesthesia?

Answer 20

Propofol

Question 21

Why is propofol a popular induction agent (aka advantages)?

Answer 21

• slow “to effect” induction w/o excitement
• rapid recovery from anaesthesia
• non-cumulative; suitable for TIVA
• suitable for thin dogs & sighthounds
• no perivascular damage
• not arrhythmogenic
• affordable

Question 22

What are the disadvantages of propofol?

Answer 22

• CVS depression
• Respiratory depression
• hypercapnia if used for TIVA
• pain on injection, short-lived
• propofol ‘twitches’/myoclonus
• shelf-life of preservative-free formulation very short (6-8 hrs)
• Propofol 28 (w/ preservative) not suitable for repeated admin/infusion due to preservative

Question 23

What is a patient that the preservative form of propofol should not be used?

Answer 23

C-sections

Question 24

What type of drug is ketamine?

Answer 24

Dissociative anaesthetic which dissociates mind & body

Question 25

What signs of anaesthetic depth are used with ketamine?

Answer 25

- active pharyngeal & laryngeal reflexes - open, central eye - nystagmus (equine) - increased muscle tone - hallucinations (humans)

Question 26

Ketamine advantage?

Answer 26

Analgesic

Question 27

Alfaxalone can be used for...

Answer 27

- induction of anaesthesia - total intravenous anaesthesia (TIVA) as CRI - Sedation (IM)

Question 28

Alfaxalone is a ... anaesthetic

Answer 28

steroid

Question 29

Injectable anaesthesia is made up by...

Answer 29

IM injections repeated IV injections or top-ups TIVA

Question 30

What drug combintions are used in small animal practice for injectable anaesthesia?

Answer 30

- Medetomidine & ketamine +/- butorphanol IM - Ketamine & diazepam IV +/- top-ups - propofol IV, to effect - alfaxalone IV, to effect

Question 31

What drug combinations are used in equine practice for injectable anaesthesia?

Answer 31

- A-2 agonist & ketamine +/- butorphanol IV - Triple Drip (GGE, Xylazine, Ketamine)

Question 32

What are the advantages of IM/IV anaesthetic techniques?

Answer 32

1. useful for quick procedures 2. useful for wild animals 3. no expensive equipment required 4. no operating room pollution 5. can reverse some agents

Question 33

What are the disadvantages of using IM/IV anaesthetic techniques only?

Answer 33

- no return of anaesthetic agents - easy to overdose - variable onset of action w/ IM inj - may be dfficult to control depth - resp depression common - may be difficult to prolong anaesthesia safely - IV injection may result in perivascular leakage - no ETT/airway protection - no anaesthetic machine or O2 - inadeq monitoring of P - not suitable for high-risk P w/o fluids & O2 - cannot resuscitate P if no airway protection/O2 support available

Question 34

What considerations should be taken into account before using IM/IV techniques of anaesthesia?

Answer 34

- use combo of drugs if possible - use drugs w/ reversal agents - monitor P throughout procedure, incl post-op - provide analgesia, O2, fluid therapy

Question 35

TIVA is used to

Answer 35

reduce inhalant anaesthetics when possible

Question 36

TIVA can be

Answer 36

a single agent or combo of IV agents

Question 37

what drugs are used for dogs in TIVA admin?

Answer 37

- Propofol & opioid (fentanyl, remifentanil) +/- NMB - Alfaxalone & opioid

Question 38

What drugs are used for horses in TIVA admin?

Answer 38

- Ketamine, alpha-2, guaifenesin ('triple drip')