Induction of anaesthesia

Question 1

What is induction of anaesthesia?

Answer 1

induction is the transition from an awake state to an anaesthetised state

Question 2

How can we induce anaesthesia?

Answer 2

usually injectable: most common IV, can also be IM
inhalational

Question 3

What does the choice of induction method depend on?

Answer 3

species and temperament of animal
underlying medical conditions
nature of procedure
available drugs, equipment and conditions
personal preference and experience

Question 4

What are the injectable induction agents?

Answer 4

propofol
alfaxolone
ketamine

thiopentone/thiopental
etomidate

Question 5

What are the inhalational induction agents?

Answer 5

isofluorane
sevoflurane

desflurane

Question 6

What are the 4 pharmacokinetic characteristics important to know with general anaesthesia agents?

Answer 6

uptake: time to reach adequate blood and brain levels, effect of route administration
distribution into tissues: depends on blood flow, may be influence by dz, lowers blood levels
metabolism: species variable, influenced by dz
elimination

Question 7

What do we need to consider with general anaesthetic agents?

Answer 7

not only dz increase anaesthetic risk
anaesthesia can impact morbidity
evaluate if ptx has problem that can affect the anaesthetic or if there is a problem the anaesthesia could worsen

Question 8

What are the actions in the CNS by GA agents?

Answer 8

dose dependent nervous system depression
continuum: sedation becomes anaesthesia

Question 9

What is the difference between low and high doses of anaesthetic agent?

Answer 9

Low: sedation (reduction of agitation to facilitate a medical procedure)
High: anaesthesia (unaware and unresponsive to painful stimuli - analgesia, unconsciousness and muscle relaxation)

Question 10

What are the effects of GA agents on the CVS?

Answer 10

CVS depression
drop in CO
vasodilation
reduced BP when monitoring

Question 11

What are the effects of GA agents on resp syst?

Answer 11

Resp depression
decrease resp rate
decrease tidal volume
reduced minute volume

Question 12

What are the analgesic effects of GA agents?

Answer 12

some provide little analgesia
administer analgesic for sx procedures

Question 13

What is nociception?

Answer 13

CNS and pain processing pathways are still stimulated during sx under anaesthesia

Question 14

What do we need to monitor during induction and why?

Answer 14

critical period w/ rapid changes as large amounts of anaesthetic agent are administered
CVS: HR, pulses, BP
Resp: rate/depth of resp
Depth of anaesthesia: changes in reflexes during induction

Question 15

What is the difference between dose and concentration?

Answer 15

Dose = mg/kg your ptx will need
Concentration = mg/ml in a solution

Question 16

What is inhalational induction?

Answer 16

induction of anaesthesia using gas

Question 17

When should we use inhalational induction?

Answer 17

aggressive ptx when IV/IM injection impossible

Question 18

What is important to not about inhalational anaesthesia?

Answer 18

increased risk of pollution and personnel exposure
may see excitement/stress during induction

Question 19

What are the different inhalant induction agents?

Answer 19

isoflurane
sevoflurane
nitrous oxide

halothane
desflurane

Question 20

What are the factors that affect inhalational agent uptake?

Answer 20

alveolar concentration of inhalant agents (inspired concentration, fgf, breathing syst vol, alveolar ventilation)
drug uptake from lungs (solubility)

Question 21

What is the blood-gas partition coefficient?

Answer 21

it describes the relative affinity of an anaesthetic for 2 phases
number of parts of gas in blood vs alveolus

Question 22

What does the partition coefficient tell us about the inhalational agent?

Answer 22

high nb means gas is very soluble in blood
speed of induction and recovery is SLOWER for more soluble agents

Question 23

Which inhalational agent is quicker?

Answer 23

halothane ++++
isoflurane++

Question 24

What are the different IV induction agents?

Answer 24

propofol
alfaxolone
ketamine
thiopentene/thiopental
etomidate
fentanyl/midazolam

Question 25

What is propofol?

Answer 25

IV induction agent a phenol can be used for induction and maintenance of anaesthesia (dogs and cats) must be given IV

Question 26

How is propofol formulated?

Answer 26

white emulsion: containing lipid (= more soluble) soya oil, egg, lecithin either no preservatives = discarded same day with preservatives= 28 day shelf life

Question 27

What is benzyl alcohol and what are its effects?

Answer 27

a preservative often used in propofol can cause prolonged recovery and hyperkinesia in cats can cause neuro signs like tremors in dogs

Question 28

What is the danger on using propofol with preservatives?

Answer 28

can cause fatalities no antidote: supportive tx dogs: lethal dose = max every h for 9h cats: lethal dose within 6.5 h of administration only licensed for induction

Question 29

What are the pharmacokinetics and properties of propofol?

Answer 29

rapid onset after injection blood levels decrease by redistribution rapid metabolism: hepatic and extra-hepatic CVS depression (vasodilation, lower BP) resp depression

Question 30

What should we know about the use of propofol in cats?

Answer 30

cats are deficient in several conjugation pathways some may have problems metabolising triglycerides due to lipoprotein lipase deficiency recovery might be slower than dogs can cause heinz body production and oxidative injury if used daily

Question 31

Why should we give propofol slowly?

Answer 31

within a minute particularly if animal deeply sedated alpha 2 agonist cause bradycardia -> slower circulation -> longer onset time

Question 32

What is alfaxalone?

Answer 32

IV induction agent neuro steroid for induction and maintenance of anaesthesia

Question 33

What are the pharmacokinetics and properties of alfaxalone?

Answer 33

poorly soluble in water so marketed with a solubilising agent (cyclodextrin) rapid onset of action, short duration cardiopulmonary depression is shorter in time to recover than propofol

Question 34

What is important to not when using alfaxalone as induction agent?

Answer 34

can see excitement on recovery if not adequately sedated

Question 35

What is ketamine?

Answer 35

IV induction agent dissociative anaesthetic induction and maintenance of anaesthesia also has analgesic actions at sub-anaesthetic doses

Question 36

How can ketamine have analgesic effects?

Answer 36

at sub-anaesthetic doses binding NMDA receptors

Question 37

What is important to note when using ketamine as an induction agent?

Answer 37

excitation and rigidity if given alone always combined with other sedative agents

Question 38

What is a common way to use ketamine in cats and dogs?

Answer 38

"triple combo" (aggressive cats and dogs) - ketamine, medetomidine, opioid IM onset of action 3-5 min, short duration procedures

Question 39

What is a common way to use ketamine in horses?

Answer 39

after profound sedation with alpha 2 agonist IV in combo with a benzodiazepine (diazepam or midazolam) to counteract muscle rigidity

Question 40

What are the effects of ketamine as an induction agent on the body systems?

Answer 40

CNS effects: cranial reflexes preserved CVS: stimulation of sympathetic NS (mild increase in BP and tachycardia, direct myocardial depression) mild resp depression analgesia

Question 41

What are the properties of thiopentene/thiopental?

Answer 41

rapid onset of action relatively slow hepatic metab cumulative: accumulates in body fat, repeated injection slow recovery (hungover effect)

Question 42

What effects are important to note about thiopentone/thipental as an induction agent?

Answer 42

irritant if administered extravascularly CV and resp depression may be seen used in horses as top up dos for induction is to effect

Question 43

What are the properties of etomidate?

Answer 43

minimal cv and. resp depression depresses adrenal gland function (cortisol production)

Question 44

When/how do we administer etomidate as an induction agent?

Answer 44

good for sick/compromised patients usually administered with midazolam unlicensed

Question 45

When do we use fentanyl/midazolam as an induction agent?

Answer 45

good for sick compromised ptx opioid and benzodiazepene

Question 46

How can you reduce the dose of your induction agent?

Answer 46

use premedication use co-induction technique (no evidence that this will reduce CV side effect) administer induction agent slowly to effect

Question 47

What IV induction agent is suggested for normal animals?

Answer 47

propofol alfaxalone

Question 48

What IV induction agent is suggested for CV dz (mild)?

Answer 48

propofol or alfaxalone with midazolam

Question 49

What IV induction agent is suggested for CV dz (severe, like sick sinus syndrome)?

Answer 49

etomidate