Anaesthesia Flashcards
pre-op assessment
- full history
- owner questioning
- previous reaction to drugs
- confirm pre-op fasting times
pre-op fasting advantages/disadvantages
- reduces GOR, regurgitation, aspiration
- prolonged starvation can increase risk of GOR
routes of admin for induction
injectable (IV / IM)
inhalant (face mask / induction)
options for airway management
mask
laryngeal (LMA)
supraglottic device (V-gel)
ETT
complications during induction
- lack of airway patency
- aspiration/regurgitation
- hypothermia
- post-induction apnoea
FGF calculation
(BW x TV) x RR x CF
Min vol x RR x CF
dosage calculation
weight x dose/strength
2nd gas effect
2 gases in alveoli, nitrous diffuses into blood first as it has a bigger conc gradient. this concentrates the second gas which can then also diffuse into blood
equine catheter placement
left jugular vein
equine anaesthetic technique
ensure 5 point stance
how to perform a pre-anaesthetic assessment
- full history
- owner questioning (temperament)
- previous reactions to drugs/anaesthetics
- full clinical examination
- confirm pre-op fasting times
- procedure
ASA classification
ASA I- normal, healthy patient
ASA II- mild systemic disease
ASA III- systemic disease, well compensated or controlled by treatment
ASA IV- severe uncompensated systemic disease
ASA V- unlikely to survive 24hrs
pre-op fasting goal
the reduce volume of the stomach contents to prevent GOR/regurgitation and aspiration
pre-op fasting recommendations
cats- 6-8hrs
dogs- 8-10hrs
rabbits/small furries- no starvation, withhold food 30 mins before
- prolonged starvation can increase GOR
informed consent facts
- legal document to be stored on patient record
- must ensure owner understands what has been signed
- give copy of consent form to owner
communication to owner
- give realistic time frames for communication
- keep communication open
oxygen cylinder storage
- molybdenum steel
- well ventilated fire-proof room
- store full and empty cylinders seperately
cylinder yolk
screw that attaches to cyclinder
- contains a bodok seal providing a gas-tight seal
- allows unidirectional flows
- pin index safety system- prevents the cylinder being attached to the wrong inlet
pin index safety system
yolk on the anaesthetic machine has 2 protuding pins
- aligned with holes on the corresponding gas cylinder
- prevents the wrong one being attached to the wrong inlet
anaesthetic pipelines
- pipelines connect the anaesthetic machine to schrader sockets which attach to main source
- schrader probes- unique diameter index
-non-interchangeable screw thread- unique profile of each nut and probe for each gas
pressure regulator
- cylinder pressure needs to be reduced to a safe level (400kPa)
- smooths any fluctuations of pressure from gas supply
pressure gauges
- indicates the pressure of gas in kPa
- cyliner pressure is proportional to vol of gas contained in it
- as cyclinder empties, pressure gauge drops
- shows when the cylinder needs to be changed
O2 failure alarm
- should sound when the supply drops below 200kPa
- should cut out nitrous oxide delivery
- not all machines will make audible noise (warning message instead)
hypoxic guard
- not present in all machines
- O2 and N2O control valves are mechanically linked
- maintains min ratio
- prevents hypoxic micture being delivered to patient
check valve/non-return pressure relief safety valve
- positioned downstream of vaporiser
- prevents backflow of gas back into machine
- protects machine not patient
check valve/non-return pressure relief safety valve
- positioned downstream of vaporiser
- prevents backflow of gas back into machine
- protects machine not patient
flowmeter/rotameter
- measures the flow of a specific gas passing through
3 parts:
1. flow control valve- allows adjustment of gas flow
2. tepered transparent tube- visual scale
3. bobbin- floats as gas passes around (higher flow= higher bobbin)
vaporizers
- found on back bar of machine
- downstream of flowmeter
- contains volatile agent/liquid anaesthetic
- as gas passes through, it picks up vapour to pass to patient
common gas outlet
- attachment of breathing system
- delivers gas/es and anaesthetic agent to patient
- if obstructed the pressure relief safety valve should open
calibrated vaporizers
- gas enters and splits into:
1. bypass channel (avoids liquid anaesthetic)
2. into chamber (above liquid anaesthetic)
TEC- temp compensation mechanism
- wicks- increase surface area for evaporation of anaesthetic
- baffles- direct incoming gas down closer to surface of liquid
O2 flush
- supplies oxygen at 400kPa and 35-75L/min
- bypasses flowmeters and vaporizer
- use can cause barotrauma
- dilution of anaesthetic gases
scavenging definition
- removal of environmental contaminants
- waste anaesthetic volatile agents
two types:
1. active
2. passive
active scavenging
- waste gases are drawn outside the building by a fan and vent system
- requires an air break to prevent negative pressure applied to patients breathing system (prevents air being sucked out of patient)
passive scavenging
- waste gas is pushed by patients expiratoru effort into tubing either:
1. tubing leading out of the building (increases difficulty to exhale due to increased resistance)
2. tubing leading to a canister containing active charcoal (doesnt absorb N2O)
advantages and disadvantages of passive scavenging
advantages:
- versatile
disadvantages:
- canister needs to be weighed regularly
oxygen concentrators
- takes in air and purifies it
- used for at home patients requiring oxygen
- uses a moleccular sieve containing zeolite which removes nitrogen leaving the air 87-95% O2
liquid O2 supply
- to be kept at -183 degrees
- passed through a vaporiser and turned into a gas before being piped inside the building
patient saftey features on anaesthetic machines
- pin index system
- ratio regulators
- nitrous oxide cut-out
- O2 failure alarm
- reserve oxygen cylinders
dead space
volume of gas that doesnt eliminate CO2
tidal volume
volume of gas entering the lung with each inspiration
minute volume
volume of gas entering the lungs within a minute
functions of a breathing system
- provide O2 +/- anaesthetic agent
- enable IPPV or spontaneous ventilation
- enable scavenging of expired gases
non-rebreathing system components
- attachment to ET tube
- inspiratory and expiratory tubes
- APL valve
- reservoir bag
rebreathing system components: circle
- soda lime canister
- tubing to ET tube, scavenging
- reservoir bag
- unidirectional valve
reservoir bag
should be 3-6 X tidal volume
breathing system tubing
coaxial (one tube lies within the other) or parallel
- parallel may increase drag but have less resistance
- beware of inner hose disconnection with coaxial systems
soda lime function
- absorbs CO2
- changes colour when exhausted (needs changing)
- water and heat produced
non-rebreathing system examples
- T-piece, bain, lack, magill
- FGF removes expired CO2
non-rebreathing system advantages and disadvantages
advantages:
- low resistance and lightweight
- some suitable for IPPV (T-piece and bain)
- cheap
disadvantages:
- higher FGF
- heat and moisture lost, expensive, increased pollution risk)
circle advantages and disadvantages
advantages:
- lower FGF
- lower pollution risk, heat and moisture retained
- suitable for IPPV
- higher resistance
minute vol calculation
tidal vol x resp rate
tidal volume calculation
use 10mL/kg as starting point
FGF calculation
minute volume x circuit factor
minimum FGF in the circle
metabolic oxygen consumption
large animals: 5mL/kg
small animals: 10mL/kg
main characteristics of T-piece
- <10kg
- circuit factor= 2-3
- suitable for IPPV
- low resistance and dead space
- 2 tubes= slight drag
characteristics of a bain
- > 8-10kg
- circuit factor= 2-3
- suitable for IPPV
- low drag and dead space
- coaxial
characteristics of a lack
- > 10kg
- circuit factor= 0.8-1
- unsuitable for IPPV
- moderate drag, resistance and dead space
characteristics of a circle
- variety of sizes
- > 15-20kg
- unidirectional valves, soda lime canister, APL valve= resistance
- FGF set at more than metabolic oxygen requirement
what happens when APL valve is left closed
- reservoir bag distends
- reduced thoracic movements
- possibly leaking around ET tube cuff
- tachycardia, hypoxia
- potential for pneumothorax/pneumomediastinum (rupture of lung or trachea)
effects of excessive resistance
- altered resp rate/pattern
- decreased tidal volume
- hypoventilation and hypercapnia
- hypoxia
effects of excessive dead space
breathing system too long
- increases PaCO2
- increases work of breathing as minute vol needs to increase to maintain normal levels of PaCO2
when is preforming procedures under sedation is appropriate in SA practice
procedures that aren’t invasive or painful that just require the animal to be still:
- radiography
- minor procedures such as wound re-dressing, de-matting
when should dogs and rabbits be extubated
- watch for signs that laryngeal reflexes are returning (swallowing)
- watch for spontaneous movement/other reflexes
when should cats be extubated
- when ear flick and blink return
- extubate before laryngeal reflexes return
- danger of laryngospasm if left too long
when should horses be extubated
- return of laryngeal reflexes
complication with pain/grimace scales
- pain can be hard to measure in prey species using grimace scale
what should be on an anaesthetic record
- TPR, pulse ox, drug doses, start and finish time
- every 5 mins
reflexes that are used to measure depth of anaesthesia- stage 3, plane 1:
- steady respiration
- pinch reflex
- no limb movement
- eye in ventro-medial position
stage 3 plane 2 measuring depth of anaesthesia
- eye ventromedial
- absent palpebral reflex
- muscles relaxed
- HR and tidal volume decrease
stage 3 plane 3 depth of anaesthesia
- eye becomes central, dilated
- HR and BP low
absent palpebral reflex and eyes ventromedial
adequate anaesthesia
palpebral reflex and central eyes
too light
no palpebral reflex and eyes central
too deep
how does anaesthesia affect hypothermia
- vasodilation increases heat loss
- thermoregulation is interfered with, reduced metabolic rate and heat produced
why is monitoring so important during anaesthesia?
- adverse affects of medication
- depth of anaesthesia
advantages of BP doppler
- inexpensive
- efficient
- quick results
disadvantages of oscillometric BP
- more expensive
- systolic, diastolic, mean
- interference, movement
advantages and disadvantages of direct BP
- gold standard, beat by beat info
- useful for long procedures
- arteries bleed
- aseptic
- invasive
types of capnography
sidestream
- not real time, needs FGF
mainstream
- real time, expensive
high end tidal CO2 causes
- hypoventilation
- reduced tidal volue
low end tidal CO2 causes
- hyperventilation
- low CO
- hypothermia
- leak in sample line, breathing system
high INCO2
- too low fresh gas flow
- too much dead space
- exhausted absorbant
advantages of capnography
- non invasive
- easy to set up and use
- effective way of monitoring
disadvantages of capnography
- dead space
- requires ET tube
limitations of pulse oximetry
- false readings
- doesn’t work on pigmented skin
- doesn’t work well in anaemia, poor perfusion
methods for maintaining anaesthesia
- TIVA
- injection
- gaseous
isoflurane, does it meet ideal agent requirements?
- irritant to MM
- peripheral vasodilation
- no analgesia
- rapid uptake and elimination
sevoflurane, does it meet ideal agent requirements?
- non irritant to MM
- poor analgesia
- high MAC
- rapid uptake and elimination
disadvantages of inhalational maintenance
- requires equipment and facilities
- mainly done in hosp environment
- personnel risks
disadvantages of injectable maintenance
- difficult to control depth
- unstable plane of anaesthesia if using bolus
- careful dosing needed
disadvantages of TIVA
- IV access essential
- long recovery after prolonged infusion
- tricky calculations
advantages of inhalational maintenance
- easy to admin
- suitable for most patients
- easy to adjust depth
advantages of injectable maintenance
- available in field
- admin by nurse
what to do during tachycardia during anaesthesia
- check for muscle tone, increased resp rate
- increase anaesthesia
- can be due to inadequate resp, hypovolaemia, drug action
what to do during brachycardia during anaesthesia
- check eye position, reflexes
- too deeply anaesthetised (turn down)
- hypothermic (check temp)
- drug action
managing hypotension during anaesthesia
- turn down anaesthesia
- IV crystalloid bolus
- replace blood loss if applicable
why do accidents and emergencies occur during anaesthesia?
- sick animal- sstabilise before procedure
- human error- checklists, communication
- equipment failure- check
- inadequate prep/monitoring
common human errors
- leaving APL valve closed
- drug admin errors
- airway management errors
- errors positioning
- inadequate eye protection
leaving APL valve closed
- reservoir bag distends
- reduced thoracic movements
- leaking around ET cuff
- tachycardia
airway management errors
- failed intubation
- traumatic intubation
- tracheal rupture
positioning errors
- pain
- comprimised ventilation
- comprimised CV function
- EPAM (equine post anaesthetic myopathy)
eye protection errors
- sedation reduces tear formation
- bland opthalmic ointment
- can lead to corneal ulceration
mechanisms of resp failure
- depression of resp centre in brain
- impaired movement of thoracic cage (sandbags)
- impaired lung movement (pleural effusion)
- airway obstruction
mechanisms of resp failure
- depression of resp centre in brain
- impaired movement of thoracic cage (sandbags)
- impaired lung movement (pleural effusion)
- airway obstruction
increased risks of anaesthesia in exotics
- size (difficult to weigh/examine)
- lack of equipment
- mouth anatomy (ability to intubate, obligate nasal breather)
- physiology (high metabolism, O2 consumption)
- temp (high SA:vol= heat loss)
- CVS (size of vessels, HR)
- GI (hind gut fermenter=gut stasis issue)
- species specific concerns
exotic species specific concerns
ferret: hyperoestrogenism
rabbit: liver torsion
poor husbandry (lack of knowledge)
Bird anaesthesia concerns
- hide illness
- stress of restraint
- complete racheal rings (do not cuff)
- movement of sternum essential to breathing
reptile/snake special considerations
- zoonosis
- husbandry= humidity, UV, light
- poikilothermic/ectothermic
- breath holding
- 3 chamber heart (shunt can cause poor gas uptake)
- avoid cuffed ET tube
tortoise special considerations
- respiration is produced by muscle movement of limbs
- low MAP
how long should guinea pigs and ferrets be starved before anaesthesia?
guinea pigs= 0-4hrs
ferrets= 6hrs
monitoring anaesthesia in exotics
reflexes (righting, withdrawal, jaw tone)
pulse oximetry
capnography
ECG
