Maintenance of anaesthesia Flashcards
Do we always have to intubate?
always recommend ET intubation regardless of method of induction or maintenance
aka yes
When can you intubate?
sufficient depth of anaesthesia
eyes rotated ventrally
minimal sluggish palpebral reflex
loose jaw tone
no swallowing reflex on stimulation
Why should we always intubate?
deliver oxygen
deliver inhalational anaesthetic if required
protect airway from occlusion or aspiration
allow ventilation to be supported if depressed
What is important to note about intubation in cats?
spray larynx with local anaesthetic to desensitize and reduce laryngospasm during intubation (lidocane spray)
What are problems we can run in with ET tubes?
if no eye, end could be blocked
sometimes it goes in one main bronchi
could get squeezed
overinflation damages trachea
Why do we have to maintain anaesthesia?
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
What are the 3 ways o maintain anaesthesia?
intravenous (TIVA)
inhalational
combo of both (PIVA)
What are the advantages of TIVA?
lower cost of equipment
environmentally friendly
less CV side effects
What are the disadvantages of TIVA?
higher cost of drugs
increased incidence of awareness
technically more demanding
rely in metabolism to recover
rely on IV access
What are the advantages of inhalational maintenance?
lower cost of drugs
rely on exhalation to recover
low level of metabolism
What are the disadvantages of inhalational maintenance?
higher cost of equipment
not environmentally friendly
What are the effects of GA agents on the systems?
CVS depression: drop in CO, vasodilation, reduced BP when monitoring
resp depression: decreased resp rate, tidal volume, minute volume)
CNS depression: unconsciousness
What are the injectable agents for maintenance?
propofol
alfaxalone
ketamine (used at low analgesic doses)
What other agents will be used with injectable agents for maintenance?
benzodiazepines
lidocaine
opioids
inhavalants (PIVA)
Is TIVA intermittent or continuous?
intermittent: concentration goes up and down a lot VS every time you top up
continuously stressing out the CVS
What are the pharmacokinetic properties of inhalational agents for maintenance?
administered + removed from body by lungs
metabolised in low percentage by liver
How are inhalational agents for maintenance absorbed and used by the body?
from alveoli agent is absorbed into blood -> brain
redistributed into other tissues including fat
What is MAC?
minimum alveolar concentration
what is required to prevent movement in response to painful stimulus in 50% of the animals
How much inhalational agent do i need?
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
What does not affect MAC?
length of anaesthesia
gender
blood pH
What factors can affect MAC?
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)
Which inhalant agent causes the most reduced cardiac output?
halothane
some with iso/sevo
Which inhalant agent has a better maintenance of respiration?
sevoflurane
Which inhalant agent is most metabolised?
halothane
What are the characteristics of isoflurane?
clear colourless liquid with a pungent smell
maintains well hepatic blood flow
myocardial protective properties
principally excreted unchanged
licensed in all species?
What is the best choice of inhalant agent for ptx with hepatic dz?
isoflurane
maintains well hepatic blood flow
What is the best choice of inhalant agent for ptx with coronary heart dz and why?
isoflurane
myocardial protective properties
limiting infarct size
improving recovery from myocardial ischaemia
What are the characteristics of sevoflurane?
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
What are the characteristics of desflurane?
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
Why can’t nitrous oxide be used as sole anaesthetic agent?
would require a MAC of 200% in animals
What are the characteristics of nitrous oxide as an inhalant agent?
mild analgesic properties
very insoluble
can produce diffusion hypoxia
atmospheric pollution: green house effect
gealth risk with long time exposure/preg
vitamin B12 deficiency
What are the factors that can influence recovery?
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
What should we do before/in recovery?
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
When should we extubate?
when swallowing reflex returns
cats might be slightlybearlier to prevent laryngospasm
later if concerned about airway protection (brachy, vomiting risk, regurgitation in ruminants)
