Maintenance of anaesthesia

Question 1

Do we always have to intubate?

Answer 1

always recommend ET intubation regardless of method of induction or maintenance
aka yes

Question 2

When can you intubate?

Answer 2

sufficient depth of anaesthesia
eyes rotated ventrally
minimal sluggish palpebral reflex
loose jaw tone
no swallowing reflex on stimulation

Question 2

Why should we always intubate?

Answer 2

deliver oxygen
deliver inhalational anaesthetic if required
protect airway from occlusion or aspiration
allow ventilation to be supported if depressed

Question 3

What is important to note about intubation in cats?

Answer 3

spray larynx with local anaesthetic to desensitize and reduce laryngospasm during intubation (lidocane spray)

Question 4

What are problems we can run in with ET tubes?

Answer 4

if no eye, end could be blocked
sometimes it goes in one main bronchi
could get squeezed
overinflation damages trachea

Question 5

Why do we have to maintain anaesthesia?

Answer 5

duration of action of IV induction agents is generally 5-10 min after which spontaneous recovery of consciousness will occur
needed to prolong unconsciousness for the required duration

Question 6

What are the 3 ways o maintain anaesthesia?

Answer 6

intravenous (TIVA)
inhalational
combo of both (PIVA)

Question 7

What are the advantages of TIVA?

Answer 7

lower cost of equipment
environmentally friendly
less CV side effects

Question 8

What are the disadvantages of TIVA?

Answer 8

higher cost of drugs
increased incidence of awareness
technically more demanding
rely in metabolism to recover
rely on IV access

Question 9

What are the advantages of inhalational maintenance?

Answer 9

lower cost of drugs
rely on exhalation to recover
low level of metabolism

Question 10

What are the disadvantages of inhalational maintenance?

Answer 10

higher cost of equipment
not environmentally friendly

Question 11

What are the effects of GA agents on the systems?

Answer 11

CVS depression: drop in CO, vasodilation, reduced BP when monitoring
resp depression: decreased resp rate, tidal volume, minute volume)
CNS depression: unconsciousness

Question 12

What are the injectable agents for maintenance?

Answer 12

propofol
alfaxalone
ketamine (used at low analgesic doses)

Question 13

What other agents will be used with injectable agents for maintenance?

Answer 13

benzodiazepines
lidocaine
opioids
inhavalants (PIVA)

Question 14

Is TIVA intermittent or continuous?

Answer 14

intermittent: concentration goes up and down a lot VS every time you top up
continuously stressing out the CVS

Question 15

What are the pharmacokinetic properties of inhalational agents for maintenance?

Answer 15

administered + removed from body by lungs
metabolised in low percentage by liver

Question 16

How are inhalational agents for maintenance absorbed and used by the body?

Answer 16

from alveoli agent is absorbed into blood -> brain
redistributed into other tissues including fat

Question 16

What is MAC?

Answer 16

minimum alveolar concentration
what is required to prevent movement in response to painful stimulus in 50% of the animals

Question 17

How much inhalational agent do i need?

Answer 17

aka what potency is needed to maintain anaesthesia
for clinical anaesthesia aim for slightly over MAC
varies between species, depends on other sedative/anaesthetic agents

Question 18

What does not affect MAC?

Answer 18

length of anaesthesia
gender
blood pH

Question 19

What factors can affect MAC?

Answer 19

hypothermia (decrease)
hyperthermia (increase)
very young (increase)
old (decrease)
severe hypoxia/hypercapnia (decrease)
severe anaemia (decrease)
severe hypotension (decrease)
CNS depressant drugs (decrease)
excitation (increase)
pregnancy (decrease)

Question 20

Which inhalant agent causes the most reduced cardiac output?

Answer 20

halothane
some with iso/sevo

Question 21

Which inhalant agent has a better maintenance of respiration?

Answer 21

sevoflurane

Question 22

Which inhalant agent is most metabolised?

Answer 22

halothane

Question 23

What are the characteristics of isoflurane?

Answer 23

clear colourless liquid with a pungent smell
maintains well hepatic blood flow
myocardial protective properties
principally excreted unchanged
licensed in all species?

Question 24

What is the best choice of inhalant agent for ptx with hepatic dz?

Answer 24

isoflurane
maintains well hepatic blood flow

Question 25

What is the best choice of inhalant agent for ptx with coronary heart dz and why?

Answer 25

isoflurane
myocardial protective properties
limiting infarct size
improving recovery from myocardial ischaemia

Question 26

What are the characteristics of sevoflurane?

Answer 26

clear colourless liquid with better smell than isoflurane
theoretically free fluoride ions released when metabolised
toxic to kidneys but no problems reported clinically
licensed in dogs and cats

Question 27

What are the characteristics of desflurane?

Answer 27

clear colourless liquid with pungent smell
very volatile agent
requires special vaporizer
exceptionally insoluble (quick induction/recovery and depth changes)
not licensed in vet species

Question 28

Why can’t nitrous oxide be used as sole anaesthetic agent?

Answer 28

would require a MAC of 200% in animals

Question 29

What are the characteristics of nitrous oxide as an inhalant agent?

Answer 29

mild analgesic properties
very insoluble
can produce diffusion hypoxia
atmospheric pollution: green house effect
gealth risk with long time exposure/preg
vitamin B12 deficiency

Question 30

What are the factors that can influence recovery?

Answer 30

animal behaviour
bad quality induction
quality of sedation in premedication (state of animal is brought back)
drugs used during anaesthesia
pain
full bladder
amount of opioid on board

Question 31

What should we do before/in recovery?

Answer 31

empty bladder
plan for extra analgesia/sedation before pts is conscious
TPR
analgesia/othe tx plan (fluid, oxygen, warm up, food)
extubate and place in kennel
pain assessment
TPR every 30-60min

Question 32

When should we extubate?

Answer 32

when swallowing reflex returns
cats might be slightlybearlier to prevent laryngospasm
later if concerned about airway protection (brachy, vomiting risk, regurgitation in ruminants)