Anaesthesia Flashcards
what is anaesthesia?
the reversible production of a state of unconsciousness required to perform surgery and diagnostic testing
what does anaesthesia rely on?
provision of the elements of the anaesthesia triad
what is general anaesthesia?
a state of unconsciousness produced by anaesthetic agents with absence of pain sensation over the entire body
what is regional anaesthesia?
insensibility caused by an interruption of sensory nerve conduction in any region of the body
what is local anaesthesia?
lack of sensation in a localised part of the body
define sedation
the allaying of irritability or excitement
define anxiolysis
reduced anxiety
define analgesia
reduced sensibility to pain
define narcosis
a sleep like state
define hypnosis
an artificially induced state of passivity (often used interchangeably with narcosis)
what is premedication?
a drug/combination of drugs given prior to the induction of general anaesthesia
why give premeds?
calms patients
aids restraint
provides pre-emptive analgesia
allows a reduction i induction and maintenance drugs
contributes to smooth induction and recovery
what is the sequence of events involved in general anaesthesia?
owner conversation/consent pre-operative examination checklist/ASA classification premedication induction maintenance recovery and post op. care
what happens during the pre-operative phase?
owner conversation about general wellbeing and informed consent
admission to the practice
what happens during the pre-operative examination phase?
full clinical exam
ASA classification
planning stage
what happens during the preoperative getting ready phase?
set up machine/equipment
prepare medication/drugs/fluids
place IV catheter (?)
premedicate patient
what happens during the induction phase of anaesthesia?
placement of IV catheter (if not placed before)
pre-oxygenation
administration of pre-med (if not already given)
administration of induction agent (propofol/Alfaxalone)
secure airway (ET Tube, V-Gel, LMA, Facemask)
what happens during the maintenance phase of anaesthesia?
anaesthesia is maintained throughout by gas, TIVA or injectables
potential placement of local and regional blocks
continue to surgery/diagnostic procedure
what is TIVA?
total intravenous anaesthesia
what happens during the recovery phase of anaesthesia?
cessation of gaseous maintenance/CRI/antagonism of injectable drugs (whatever is maintaining anaesthesia)
removal of airway device when safe
move to well ventilated/quiet/calm recovery area
what are the 3 elements of the anaesthetic triad?
analgesia
narcosis
muscle relaxation
can all aspects of the anaesthetic triad be achieved with one drug?
no - multi-modal approach needed
define balanced anaesthesia
anaesthesia produced by smaller doses of two or more agents considered safer than the usual large dose of a single agent
what is a key benefit of balanced anaesthesia?
side effect of each drug are reduced
what are the main reasons for anaesthesia?
facilitate surgical/diagnostic/other procedures
prevent pain/ suffering
research
immobility
what did the CEPSAF Enquiry look into?
relative risk of poor outcome (death) of a patient undergoing anaesthetic. Shows % risk of death
what is the overall CEPSAF risk for dogs?
0.17%
what is the overall CEPSAF anaesthetic risk for cats?
0.24%
what is the overall CEPSAF anaesthetic risk for rabbits?
1.39%
what did the CEPSAF Enquiry look into?
complications within a 48hr post operative period
when did the CEPSAF enquiry find 50% of anaesthetic deaths occurred?
within 3 hours of recovery
what made anaesthetic risk higher?
sick animals
cats
ET tube intubation in cats but not dogs
is anaesthetic risk higher in sedation or GA?
GA
what was horses overall calculated anaesthetic risk according to CEPEF?
2.1% (rising to 11.7% for colic cases)
what are some species specific issues with anaesthesia?
extremes of size hyper/hypothermia aggression drug sensitivities obesity
how do extremes of size pose problems during anaesthetic?
very large to very small requiring wide range of equipment
how does aggression pose problems during anaesthetic?
risk of injury - can’t perform pre op exam and may need extra equipment
stress to animal from handling
may rely on drugs that are not ideal for the animal
may need to extubate early and remove IV lines before animal is fully awake
how may drug sensitivities in some breeds pose problems during anaesthetic?
some large dogs may require lower mg/kg than their smaller friends
how does obesity pose problems during anaesthetic?
IM injection is difficult (for premed)
can easily overdose as liver does not match weight
ventilatory compromise due to weight of excess fat on body when positioned for surgery
increased CV workload
what are some breed specific issues with anaesthesia relating to brachycephallic dogs?
compromised airways (small trachea, extra pharyngeal tissue)
gastro-oesophageal reflux
occular issues (extra lubricant and care required)
skin problems
skeletal issues
how may gastro-oesophageal reflux be prevented in brachycephallic dogs?
give omeprazole 7 days prior to surgery to reduce stomach acid
use cuffed ET tubes
raise head until cuff inflated
what are some breed specific issues with anaesthesia relating to boxers?
intolerant to acepromazine which can cause bradycardia and hypotension
cardiomyopathy which can be seen in otherwise healthy animals and cause ventricular tachycardia, arrhythmia and syncope
how can breed specific issues with boxers be avoided?
don’t give ACP
ECG before procedure to check for cardiomyopathy
in what breeds is multi drug resistance seen?
collies
sheepdogs
shepherds
what does the MDR1 gene do?
removes drugs from the brain
what happens in animals with MDR1 gene mutation?
defect in the P-glycoprotein that transports drugs meaning that toxins cannot be transported away from the brain and so build up which can cause neurological symptoms
what are the 3 key drugs that are not managed by animals with the MDR1 gene mutation?
ivermectin
butorphanol
acepromazine
what are some breed specific issues with anaesthesia relating to greyhounds?
lack cytochrome P450 which is an important clearance mechanism and so affects metabolism of drugs
body fat is very low (17%) so will recover slowly, require padding and careful temperature monitoring
what are some breed specific issues with anaesthesia relating to dobermen?
Von-Willibrand deficiency which affects clotting time dilated cardiomyopathy (found in 50% of 6 year olds) which causes heart to function less well
how should Dobermen be tested for Von Wiliibrand factor deficiency and DCM?
BMBT
ECG
what is the key legislation associated with anaesthesia?
protection of animals (anaesthetics) act
misuse of drugs act and misuse of drugs regulations
veterinary surgeons act - schedule 3
where can guidance for anaesthesia be found?
AAHA anaesthesia guidelines for dogs and cats
AAFP feline anaesthesia guidelines
Association of Veterinary Anaesthetists
American College of Veterinary Anaesthesia and Analgesia
when must the pre-operative assessment take place?
before the administration of medication/premedication
what observations/questions should be involved in the pre-operative assessment?
full history
owner questioning on health/routine/behaviour etc
previous reactions to drugs/anaesthetics
procedure
breed/species
confirmation of pre-operative fasting times
what influence does the procedure have on the pre-operative assessment?
influences questions asked and elements of the exam
what parameters should be included in the pre-operative clinical exam?
full clinical exam MM CRT thoracic auscultation pulse rate and quality ventilatory effort temperature swellings/distention
what is assessed during thoracic auscultation in the pre-operative exam?
presence of heart murmur, ventilatory effort and RR
what pulses should be felt to assess pulse quality and perfusion?
peripheral
where should the clinical exam of the pre-operative assessment be started from?
a distance - note the animals temprament
what should be checked for significant findings during the pre-operative assessment?
history
why is a systematic approach to the clinical exam of a pre-operative assessment important?
nothing is missed
repetition will increase speed
what are the levels of ASA classification?
ASA 1-5 and E
what does E denote in the ASA classification?
emergancy
describe ASA I classification
normal healthy animal
describe ASA II classification
mild systemic disease
describe ASA III classification
Systemic disease, well compensated or controlled by treatment
describe ASA IV classification
severe uncompensated systemic disease
describe ASA V classification
unlikely to survive 24 hours
why is using ASA classification important?
identifies risk
increase safety of patient
quick
according to ASA which catergories are at low risk?
I and II
according to ASA which categories are at risk?
III-IV
what is the goal of pre-operative fasting?
reduce volume of stomach contents
prevention of GOR, regurgitation and aspiration
why is reducing the volume of stomach contents through preop fasting crucial?
aids ventilation
what is the suggested length of pre-op fasting time for cats?
6-8 hours
what is the suggested length of pre-op fasting time for dogs?
8-10 hrs
what is the suggested length of pre-op fasting time for rabbits and small furries?
no starvation needed but may be worth withholding for 30mins pre-op to remeove food from mouth
what is an effect of prolonged pre-op starvation?
increase in GOR
in cats it does not necessarily mean an empty stomach
why does prolonged starvation not necessarily mean an empty stomach in cats?
stress, meal size and a lack of dietary moisture (dry food) can slow gastric emptying
what has been shown to reduce incidence of GOR?
feeding small canned food 3 hours pre-op
what must be gained at all times for all procedures?
informed consent
what is involved in informed consent?
consent form alongside a discussion with client
what should be provided to the client once the consent form is signed?
a copy
is a consent form a legal document?
yes
why must a consent form be filled in in a private area?
GDPR
allows room for client to ask questions
how can communication with owners be most effective?
give realistic time frames and stick to them
utilise text/email after initial phone call
keep communication open
listen
give privacy and space
who launched anaesthetic safety checklists?
WHO in 2008
what is the benefit of surgical checklists?
reduction in rate of deaths and surgical complications by as much as 1/3
what are the 3 categories on the ASA anaesthetic safety checklist?
pre-induction
pre-procedure
recovery
what are the 3 categories on the recommended procedures section of the ASA checklist?
pre-anaesthesia
anaesthetic machine
drugs/equipment
what must be considered when using drug/anaesthetic protocols?
each patient must be treated as an individual and previously devised protocols must be made to meet patient needs and risk factors
what diagnostic tests may be used in a pre-op assessment?
bloods urine radiography ECG echocardiology ultrasound
what is a crucial element of anaesthesia?
patient preparation
where do the majority of complaints that surround anaesthesia and veterinary medicine arise from?
poor communication
what are the 2 main options for induction of anaesthesia?
injectable
inhalent
what are the benefits of IV injected anaesthesia induction?
quick (2-10 mins onset)
reliable
expected efficacy
less stress for animal
what are the disadvantages of IV injection of anaesthetic induction?
relies on presence of IV catheter which may be tricky
what are the benefits of IM injected anaesthesia induction?
fairly quick (10-20 mins) reliable if actually IM
what are the issues with IM injected anaesthesia induction?
in obese animals can be injected into fat (less effective)
painful
slower onset
what are the benefits of SC injected anaesthesia induction?
easy
less painful than IM
what are the disadvantages of SC injected anaesthesia induction?
causes pain
longer onset (30-45 mins)
lower efficacy
what must be checked before administering a drugs by different routes?
what it is licensed for
what are the benefits of chamber anaesthesia induction?
great for small animals (hamsters/mice)
easy to set up and use
cheap
no technical skill needed
what are the disadvantages of chamber anaesthesia induction?
very stressful for the animal difficult to observe/monitor animal risk of staff exposure unpleasant only when injection isn't possible
what are the benefits of face mask anaesthesia induction?
cheap
easy to set up and use
can give oxygen and/or volatile agent quickly
what are the disadvantages of face mask anaesthesia induction?
does not protect airway
increases dead space
human exposure to VA/waste gases
not always tolerated - animal should be premedicated wherever possible
what are the risks associated with physical restraint during anaesthesia induction?
stress becoming worse/escalation (cats particularly) respiratory compromise cardiac arrhythmias raised ICP/IOP pressure on jugular coughing
why is positioning of an animal so important?
facilitates placement of tubes/catheters/blocks
ensures animal safety (better anaesthesia/procedure)
ensures personnel safety
prevents injury to all
what are the 4 main airway management devices?
mask laryngeal mask (LMA) supraglottic device (V-Gel) Endotracheal tube
what is the advantage of a laryngeal mask?
easy to use (sits over larynx)
reduced complications compared to ET tubes
reduced airway pollutants compared to face masks
what is the disadvantage of LMA?
not really designed for veterinary patients
how do supraglottic airway devices (V-Gels) work?
species and weight specific design
sits in the pharynx and mimics the anatomy
what is the gold standard method for airway protection during anaesthesia?
ET tubes
what are the main advantages of ET tubes for airway management?
allows airway protection
prevents atmospheric exposure
allows accurate provision of anaesthetic gases
what is the purpose of murphy’s eye - seen on the distal end of ET tubes?
another site for movement of air if the main lumen becomes blocked
what is the role of a pilot balloon of an ET tube?
allows inflation of the cuff
what is the role of the adapter on an ET tube?
connects to the breathing system
what does the size in mm on the side of ET tubes show?
internal diameter
what are the 4 main types of ET tube?
silicone
PVC
red rubber
armoured
what is the role of an armoured ET tube?
has internal wire which prevents the tube becoming kinked when a patient has to de positioned awkwardly
when must armoured ET tubes never be used?
if patient is to be MRI’d
what is the point of a cuff on an ET tube?
allows tight seal in trachea
if inflated correctly is safe
prevents gas leaking around tube
prevents anything going into patients lung (aspiration)
allows accurate delivery of VA and oxygen
allows direct route to lungs (suction)
what are the safest type of ET tube cuffs?
high volume, low pressure
cuff pressure is spread over a wide area increasing the safety for the patient and reducing risk of damage
why are clear tubes safer?
can see debris/dirt
condensation can be viewed to check if tube is in correctly
should ET tubes be cleaned?
no! single use design
how should the correct length of ET tube be measured?
incisors to shoulder tip
what are the issues associated with an ET tube that is too long?
risk of single lung ventilation
increase in dead space
what equipment is required for endotracheal intubation?
laryngoscope tubes in a range of sizes local anaesthetic (cats - intubeaze) tie cuff syringe swab suction? mask for preoxygenation stylet/bougie
what size blade on a laryngoscope should be used?
one that will reach the epiglottis
what must be avoided when intubating/holding an animal for intubation?
no fingers in the mouth
how are ET tubes secured once they are placed?
attached to breathing system
tie is tied around tube and then around the back of the animals head/over the nose
describe the correct process for inflation of ET tube cuff
** check textbook**
what is the gold standard for confirmation of the correct placement of ET tubes?
capnograph trace
how else can correct placement of ET tube be checked?
visualisation of tube between the vocal folds
condensation inside tube
appreciation of air movement
why should you not press on the thorax to check for ET tube placement?
false positive (air from stomach) reflux reduction in functional residual capacity of lungs
what is the best position for intubation of rabbits?
as upright as possible
why is ET tube placement in rabbits so hard?
visualisation without endoscopy is very difficult
have to go in blind
what are the 6 main common complications during anaesthetic induction?
injury (staff or patient) lack of airway patency aspiration/regurgitation hypothermia effect of anaesthetic agents on CVS and respiratory system post-induction apnoea
what can be done to prevent aspiration/regurgitation on induction?
identify at risk patients
head up induction for those at risk
what is a common cause of hypothermia on induction?
IM premed (blanket over animal in kennel)
what can cause post induction apnoea?
drug given quickly
expected side effect
what must be balanced if post-induction apnoea is seen?
hypercapnia which will encourage patient to breathe and hypoxia which is dangerous
what must be done as soon as possible after patient is induced?
monitor monitoring equipment attached assume it is all down to you and check everything check peripheral pulses confirm ventilation
when are injectable anaesthetic agents used?
induction of anaesthesia before administration of an inhalational agent
adjunct to inhalational anaesthesia
short term anaesthesia
TIVA
what are the 4 most common injectable anaesthetic agents?
propofol
alfaxalone
ketamine
tiletamine/zolazepam
what injectable anaesthetic agents are licensed for use in dogs and cats?
propofol
alfaxalone
ketamine
tiletamine/zolazepam
what injectable anaesthetic agents are licensed for use in horses?
ketemine
what injectable anaesthetic agents are licensed for use in rabbits?
alfaxalone
what drugs are used for euthanasia?
pentobarbital
secobarbital sodium
cinocaine hydrochloride (Somulose)
what factors affect the effect of drugs?
blood flow to the brain amount of non-ionized drug lipid solubility molecular size concentration gradient protein binding distribution metabolism excretion
describe the characteristics of the ideal injectable anaesthetic agent
rapid onset non irritant minimal cardiopulmonary effects rapidly metabolised and eliminated non-cumulative good analgesia good muscle relaxation
where does propofol have it’s effect?
GABA agonist - enhances inhibitory neurons in the CNS
does the plasma bound portion of a drug exhibit any effect?
no
how fast is the onset of action of propofol?
rapid
what level of plasma protein binding is seen with propofol?
high - 96-98%
is propofol lipid soluble?
yes
why will propofol have more effect in hypoalbuminaemic animals?
less protein to bind to, more then free to cross blood brain barrier and have effect
how is propofol metabolized?
in the liver
how quickly is propofol metabolized?
rapidly
is propofol non cumulative?
in dogs but not in cats
what is common post induction with propofol?
post-induction apnoea
what are the effects of propofol on the CVS?
hypotension due to myocardial depression and peripheral vasodilation
does propofol provide analgesia?
no
what level of muscle relaxation does propofol provide?
adequate for surgery - some twitching may be seen
what can continued propofol use in cats cause?
Heinz body anaemia with consecutive day use
is propofol irritant if given perivascularly by accident?
no
is there pain associated with propofol on injection?
yes
what form is propofol presented in?
egg protein or lipid emulsion
what differences in propofol formulations are there?
some contain preservatives which mean that they do not need to be discarded after they have been broached and used once
what may be added to propofol as a preservative?
benzyl alcohol
how long can propofol containing benzyl alcohol as a preservative be stored fr after opening?
28 days
when should preservative containing propofol not be used ?
prolonged infusions (e.g. TIVA)
what type of anaesthetic is alfaxalone?
steroid anaesthetic
why is alfaxalone combined with cyclodextrin?
alfaxalone itself is insoluble - the addition of this sugar allows it to become soluable
what is the theraputic index of alfaxalone?
high
is alfaxalone irritant?
no - although possible some irritation IM
what level of plasma protein binding is alfaxalone associated with?
20%
how quick is the onset of effects of alfaxalone?
rapid
is alfaxalone rapidly metabolised and eliminated?
yes
is alfaxalone suited for TIVA?
yes as it is non cumulative
why is alfaxalone suited to TIVA?
it is non cumulative
what respiratory effects are seen after anaesthetic induction with alfaxalone?
some respiratory depression - post induction apnoea
what are the effects of alfaxalone on the CVS?
preserves baroreceptor tone so that heart rate will increase with reduced BP. Leads to transient tachycardia
why does alfaxone cause transient tachycardia?
HR increases as BP goes down as baroreceptor tone is preserved
how old should patients be before alfaxone is used due to marketing authorisation?
> 12 weeks
what type of anaesthetic is ketamine?
dissociative anaesthetic - NMDA agonist
is ketamine a good muscle relaxant?
no - should not be used as sole agent but alongside BDZ or alpha-2 agonist
are reflexes maintained when ketamine is given?
yes - central eye, palprebal reflex, swallow may be present
how does ketamine maintain CV and respiratory function?
sympathetic stimulation which causes release of adrenaline that counters the ionotropic effect of ketamine on the heart meaning there is no suppression
what is ketamine’s analgesic effect?
analgesia and antihyperalgesia
how fast is the onset of effect of ketamine?
slow
is ketamine cumulative?
no and neither is metabolite nor-ketamine
what may prolong duration of ketamine action?
renal dysfunction causing slower removal of nor-ketamine from system. This has a similar effect to ketamine
what percentage plasma bound is ketamine?
50%
how is ketamine often used in horses?
IV induction and as part of TIVA techniques for maintenance of anaesthesia
when is ketamine often used in cats?
IM as sedation or for induction of anaesthesia as part of a triple/quad
what is an effect of ketamine that means it must be used cautiously in certain paitents with underlying conditions?
increases IOP and ICP
how may tiletamine/zolazepam (Zoletil) be administered?
IM or IV
what is linked to poor recovery from administration of tiletamine/zolazepam (Zoletil)?
repeated dosing
what s the difference in pharmacokinetics of tiletamine/zolazepam (Zoletil) between cats and dogs?
dogs metabolize zolazepam much faster that tiletamine leaving it unbalanced
what type of drug is thiopental?
barbiturate
what type of receptors does thiopental work at?
GABA receptor agonist
what form does thiopental come in?
pwder made up to 2.5 or 5%
why may thiopental cause perivascular tissue necrosis?
due to its strongly alkaline nature
what can be caused by perivascular injection of thiopental?
perivascular tissue necrosis
how quick is the onset of effect of thiopental?
rapid
how plasma protein bound it thiopental?
high - 80%
what happens to thiopental before metabolism?
redistribution to tissues and then metabolism
in what animals is thiopental associated with prolonged recovery?
sight hounds
why does thiopental cause prolongued recovery in sighthounds compared to other dog breeds?
different metabolic pathways present
what effects does thiopental have on CVS?
moderate, short lived cardiorespiratory depression and ventricular bigeminy (alternating sinus and PVC)
what is ventricular bigeminy?
sinus rhythm followed by PVC (premature ventricular contraction)
in what animals is the effect of thiopental particularly predictable?
horses
what 6 factors will affect recovery from injectable anaesthetics?
drug factors including dose species, breed and age co-morbidities hypothermia individual co-morbidities additional factors - concurrent drug administration
what co-morbidities must be considered that will affect recovery from injectable anaesthetics?
hepatic function
renal function
cardiovascular function
how does cardiovascular function affect recovery from anaesthetics?
affect elimination of anaesthetic via distribution and movement to kidneys
how will hypothermia affect recovery from injectable anaesthetics?
metabolism is slowed and renal plasma flow reduced
when may TIVA be used?
to reduce exposure to inhalant anaesthetic agents
no access to anaesthetic machines - e.g. horses at a yard
specific conditions for whom TIVA is safer
what are the ideal properties of drugs used for TIVA?
rapid metabolism and elimination
fast onset
high therapeutic index
pharmacokinetic info available via data sheet
what are the most common injectable anaesthetics used in practice?
propofol
alfaxalone
ketamine
what is the main use of injectable anaesthetics?
IV induction (although also used through IM and TIVA)
what is the key role of an anaesthetic machine?
delivery of oxygen (or other gas) and a volatile agent to the patient
what are the 2 ways oxygen may be provided to the anaesthetic machine?
small cylinder attached to the trolley the machine is situated on
pipeline feeding from a larger bank outside the theatre
what are cylinders made of?
molybdenum steel
what are the key considerations for the storage of gas cylinders?
under cover
dry and clean
ideally indoors - well ventilated, fireproof room
not subjected to extreme heat or cold
away from flammable/combustible materials
what cylinders should be stored separately?
full and empty
what orientation should F, G and J cylinders be stored?
vertically
what orientation should C, D and E cylinders be stored in?
horizontally
what signs should be posted around cylinder storage area?
no smoking
how should cylinders be carried?
use trolley or hold correctly
what is the role of the cylinder yolk?
holds the cylinder in place
provides a gas-tight seal
allows unidirectional flow
what is a key safety feature of the cylinder yolk?
will only fit a specific gas canister within it which prevents attachment of the wrong type of gas cylinder to the inlet
what speed should cylinder yolks be opened?
slowly
what is the BODOK SEAL?
non-combustable neoprene washer with a copper ring
what is the role of the BODOK SEAL?
prevents gas leak
what should be avoided when handling cylinder yolk?
over tightening
oils and moisturiser on hands
why should oils and moisturiser on hands be avoided when handling the cylinder yolk?
fire risk due to high pressures and flammable gases
what is the pin index safety system?
yoke on the anaesthetic machine has 2 protruding pins which align with 2 holes on the corresponding gas cylinder
what is the purpose of the pin index safety system?
prevents the incorrect cylinder being fitted to the incorrect inlet
how many holes are on the pin index safety system?
7
what pins are found on an oxygen cylinder?
2 and 5
what pins are found on a nitrous oxide cylinder?
3 and 5
what pins are found on a medical air cylinder?
1 and 5
what pins are found on a carbon dioxide cylinder?
1 and 6
what pins are found on a entonox cylinder?
7
where is piped gas supplied from?
a main source outside of theatre
where does piped gas feed into?
colour coded and labelled pipelines
what connects the anaesthetic machine to Schrader sockets?
flexible pipelines
what are Schrader sockets?
attachment point for gas pipeline in the wall which will only accept a unique diameter index collar
what are the key parts of a gas pipeline from socket to anaesthetic machine?
Schrader probe - flexible colour coded pipe - non interchangeable screw thread
what is the role of a Schrader probe?
prevents misconnection of the wrong gas
what is a Schradar probe?
unique diameter index collar which matches corresponding Schradar socket
what is a non-interchangeable screw thread (NIST)?
nut and probe with unique profile for each gas with a one way valve to guarantee unidirectional flow
what is the role of NIST?
prevents incorrect attachment of wrong gas
how many banks of cylinders are linked to a pipeline?
two banks
why are there always 2 banks of cylinders attached to a pipeline?
one in use and one reserve
what happens if oxygen in cylinder banks becomes too low?
alarm will sound
what material is gas pipework made of?
copper
why is gas pipework made of copper?
handles high pressure well
where may Schradar sockets (pipeline outlets) be located?
in the wall or ceiling mounted
what must be done to ensure pipe is secure?
tug test
what colour are oxygen cylinders?
white
what colour are medical air cylinders?
black with white collar
what colour are nitrous oxide cylinders?
blue
what is the pressure within an oxygen cylinder?
13700 Kpa
what is the pressure within a nitrous oxide cylinder?
4400 Kpa
why is the Kpa within nitrous oxide cylinders so much lower than within oxygen cylinders?
nitrous oxide is a liquid with vapour on top
what is the volume of an oxygen E cylinder?
680l
what is the volume of an F size oxygen cylinder?
1360l
what is the volume of an J size oxygen cylinder?
6800l
what would an E size cylinder be used for?
side of machine oxygen supply
what would a size J cylinder be used for?
piped oxygen supply
what is the role of the pressure regulator?
regulates gas from the cylinder to anaesthetic machine
why is a pressure regulator essential?
cylinder pressure is high (>10 000 Kpa) and needs to be reduced to a safe level that will not damage the anaesthetic machine and patient
what is a safe pressure level for gas to enter the anaesthetic machine?
around 400 kPa
what are the 4 key jobs of the pressure regulator?
reduces the cylinder pressure to a suitable supply pressure
compensates as the cylinder content decreases
smooths any fluctuations from gas supply
ensures safe delivery of gas at a manageable pressure
what is indicated by pressure gauges?
pressure of gas within cylinder and pipeline in kPa
how can you tell which gauge is for which cylinder?
colour coded
what is pressure in the cylinder proportional to?
volume of gas contained within it
what happens to the pressure gauge as the cylinder empties?
pressure gauge drops
what can the pressure gauge be used to determine?
when the cylinder needs to be changed
why must you be cautious when reading a nitrous oxide pressure gauge?
as nitrous is a liquid which then vaporises as it is used the pressure will remain relatively constant until the liquid is depleted when it will fall quickly
when will the oxygen failure alarm sound?
when oxygen supply falls below 200 kPa
what else should happen alongside the o2 failure alarm sounding?
delivery of nitrous oxide should be cut out
what may make it possible to deliver 100% N2O to the patient if oxygen fails?
if there is pressure in the oxygen line
what other mechanism should prevent delivery of 100% N2O?
hypoxic guard system
what may some machines use to inform you of low oxygen?
warning message on the scree
do all machines have nitrous oxide cut off?
no
how does nitrous oxide cut off prevent a hypoxic mixture being delivered to the patient?
flow of nitrous oxide is dependent on oxygen pressure
if oxygen pressure falls below 130-70 kPa the nitrous oxide supply will be cut off
at what oxygen pressure will the nitrous oxide cut off occur?
130-70 kpa
is hypoxic guard found on all machines?
no
how does hypoxic guard work?
oxygen and nitrous control valves are mechanically linked
both valves can be adjusted independently but the link maintains the minimum ratio of oxygen:nitrous
can nitrous oxide be turned on independently of oxygen on an anaesthetic machine with hypoxic guard?
no
what ratio of oxygen to nitrous oxide is the lowest allowed by hypoxic guard?
20-25%
on a machine with hypoxic guard what happens when nitrous oxide is turned on?
oxygen flowmeter is activated
on a machine with hypoxic guard what happens when oxygen is turned off?
so is nitrous oxide
where is the check valve/non-return pressure relief safety valve located?
downstream of vapouriser
what is the role of the check valve/non-return pressure relief safety valve?
one way valve preventing backflow of gas into the machine and creation of back pressure
when does the check valve/non-return pressure relief safety valve open?
when the back bar pressure (location of vapouriser) is >35 kPa
what is the purpose of the check valve/non-return pressure relief safety valve?
protects the machine not the patient
does each gas have it’s own flowmeter?
yes
what is the key role of a flowmeter?
administration of chosen level of fresh gas
what do flowmeters measure?
flow of gas passing through them
why must you be cautious when using low flow gas through a flowmeter?
accuracy of +/- 2.5%
what happens when flowmeters are turned on?
small amount of oxygen is released (residual flow)
what is the minimum flow of gas through a flowmeter?
200-300 ml/min
what are the 3 parts of the flowmeter?
flow control valve
tapered transparent tube
lightweight rotating bobbin or ball
what is the role of the flow control valve on a flowmeter?
allows fine adjustment of gas flow and reduces gas pressure from 420kPa to 100 kPa
what is the role of the tapered transparent rube of a flowmeter?
visual scale
what happens within the tapered transparent tube of the flowmeter when the valve is opened?
gas enters
what is the role of the lightweight rotating bobbin or ball of a flowmeter?
floats within the tube as gas passes around it
what does higher floating of the flowmeter bobbin or ball mean?
higher flow
where should flow be read from on a flowmeter with a bobbin?
the top of the bobbin
where should flow be read from on a flowmeter with a ball?
centre of the ball
what is the role of the white dot on the bobbin of a flowmeter?
confirms flow by rotating
where are vaporisers located?
back bar of the anaesthetic machine
where are vaporisers located in relation to the flowmeter?
downstream
what is contained within a vaporiser?
volatile liquid anaesthetic agent (e.g. isoflurane
what is passed through the vaporiser?
gas from the flowmeter
what happens to gas from the flowmeter as it passes through the vaporiser?
picks up vapor to deliver to the patient
what happens to gas when it enters a calibrated vaporiser?
splits into 2 streams - bypass channel and chamber above liquid anaesthetic
how is the ratio of gas that enters the bypass channel and vapour chamber adjusted?
control valve (numbers on top!)
what can be done by adjusting the ratio of gas that enters the bypass channel and vapour chamber?
concentration of vapor picked up by gas cna be increased or decreased
what is the control valve of the vaporiser controlled by?
large dial on the front of the vaporiser
why is the vaporiser housed in a block of brass?
to minimise the effect of temperature cooling
what happens as the temperature of the vaporising chamber drops?
the bi-metallic strip bends and moves, reducing resistance to flow allowing greater ratio of gas to pass into the chamber (overdose)
are calibrated vaporisers agent specific?
yes
when does cooling occur in calibrated vaporisers?
during vaporisation
what is a vaporiser sometimes known as?
temperature compensation mechanism
what is the role of wicks in a calibrated vaporiser?
increase surface area for evaporation of anaesthetic liquid
what is the role of baffles in calibrated vaporisers?
direct incoming gas down closer to the surface of the liquid
what must not happen when vaporisers are moved?
must not be tipped
where are the vaporiser(s) connected to the anaesthetic machine?
back bar
what is the role of Selectatec and Interlock systems?
provides mounting of two vaporisers on the back bar
when using Selectatec and Interlock systems can vaporisers be used at once?
no - only one can be turned on and gas will only flow through the one in use
what attaches to the common gas outlet?
breathing system
what is the role of the common gas outlet?
delivers gas(es) and anaesthetic agent to the patient
what happens if the common gas outlet is obstructed?
pressure relief safety valve should open to prevent damage to the machine
what is the role of oxygen flush?
removal of gas quickly in an emergency (not when the patient is attached)
what pressure and speed is oxygen supplied by oxygen flush?
400kPa and 35-75 l/min
what does the oxygen flush bypass?
flowmeters and vaporiser
what could be caused by using the oxygen flush when the patient is attached?
barotrauma (lung damage)
dilution of anaesthetic gases
what should be used to fill reservoir bag if empty/low?
flowmeter
what is scavenging?
removal of environmental contaminants
what regulations are waste anaesthetic volatile agents and gases subject to?
COSHH and Health and Safety at Work Act
what are the 2 types of scavenging?
active
passive
how does active scavenging work?
(torbridge)
waste gases and anaesthetic agents are drawn outside of the building by a fan and vent system
what is required in an active scavenging system to ensure negative pressure is not applied to the patients breathing system?
air break
what is the role of the air break in active scavenging?
ensure negative pressure is not applied to the patients breathing system
how does passive scavenging work?
gas is pushed by patients expiratory effort into tubing either leading outside the building or into a canister containing active charcol
what is the issue with passive scavenging via a tube leading outside the building?
makes it harder for the patient to exhale due to increased resistance
what does passive scavenging by activated charcoal not absorb?
nitrous oxide
why must passive scavenging systems into activated charcoal be weighed regularly?
to check if they are used up
what are the benefits of passive scavenging?
can be moved around
easy to use
what are the disadvantages of passive scavenging into active charcoal?
needs to be stored carefully before disposal as heat can cause it to release its contents
must be changed regularly
how do oxygen concentrators work?
takes in air and purifies it using a molecular sieve containing a material called Zeolite that removes nitrogen from the air leaving the remaining air 87-95% oxygen
when is oxygen concentration often used?
ICU units
oxygen for anaesthesia
how must liquid oxygen be stored?
-183 degrees
what is liquid oxygen stored in?
vacuum insulated evapourator
where is liquid oxygen stored?
outside
what happens to liquid oxygen before it can be piped into the hospital?
drawn off as required, passed through a vapouriser and turned into gas
what regulates the flow of gas from the vacuum insulated evapourator before it enters the pipework system?
control panel
what is required to ensure adequate oxygen supply in the event of any primary supply system failure?
backup cylinder manifolds
what are the dangers associated with liquid oxygen?
burns
frostbite
hypothermia
what are the 8 key patient safety features on anaesthetic machines?
pin-index system and NIST for pipelines colour coded pressure gauges and flowmeters oxygen flowmeter is touch coded ratio regulators nitrous oxide cut out alarm air intake valve reserve oxygen cylinders
what is touch coding of the oxygen flowmeter?
it is the easiest dial to turn
what does chronic exposure to volatile agents increase the risks of?
spontaneous miscarriage
congential malformation (men and women affected)
liver and kidney damage
what 10 ways can exposure to volatile agents be reduced?
well ventilated theatres/recovery areas
IV induction where possible
cuffed ET tubes
connect animal to breathing system before turning on gases
use low flows
check for leaks
flush breathing system with oxygen before disconnecting animal
use key fill vapourisers
fill vaporisers at the end of the day
monitor personnel exposure to anaesthetic gases
why do recovery area need to be well ventilated?
patients will be breathing out gases
how many air changes per hour should their be in theatres and recovery areas?
15-20
how should the breathing system be flushed with the animal still attached?
animal remains connected to system with just oxygen at the end of the procedure
why is nitrous oxide no longer used by many practices?
very bad for the environment
describe the process of preforming an anaesthetic machine check
scavenging connected to wall, red block will move up inside to show connection. Check piping and connect to common gas outlet
plug in gases
turn on machine and note residual flow on flowmeter (if expected)
turn O2 flow up to the top, then drop to 4 l/min (repeat with all present pipelines)
turn on N2O with no O2 - this should cut out
disconnect O2 from wall - use flush to clear system - alarm should sound. Replace O2 into wall and tug test
with just O2 - detach scavenge and occlude end. Flowmeter bobbin should move up and down showing no leaks
check vaporiser has enough agent, is securely attached and there is free movement of dial (O2 off at this point)
define dead space
volume of gas which doesn’t eliminate carbon dioxide
define tidal volume
volume of gas entering the lung with each inspiration
define minute volume
volume of gas entering the lungs each minute
define metabolic oxygen requirements
amount of oxygen required each minute for metabolic processes
define rebreathing
occurs when the inspired gas(es) reaching the alveoli contain more CO2 than can be accounted for by mere re-inhalation from the patients dead space gas (negligable)
what is the formula required to calculate minute volume?
tidal volume x respiratory rate
what must be detected when using breathing systems?
rebreathing
what are the 3 key functions of a breathing system?
provide oxygen +/- anaesthetic agent
enable IPPV or spontaneous ventilation
enable scavenging of expired gases
where does a breathing system attach to the anaesthetic machine?
common gas outlet
how does the breathing system attach to the patient?
via ET tube or mask
what does IPPV stand for?
intermittent positive pressure ventilation
what is the fresh gas flow?
oxygen/nitrous/air from flowmeters
why is scavenging of expired gases so important?
removes CO2
removes waste anaesthetic gases
why must CO2 be removed once expired from the patient?
causes:
adrenaline release
tachycardia
tachypnoea
what condition can high levels of CO2 mimic?
light plane of anaesthetic
identify the components of this non-rebreathing system and the type of system it is
Ayres T-Piece (clockwise from top) 1. APL valve 2. reservoir bag 3. connector to common gas outlet 4. breathing system tubing 5. connection to ET tube or mask 6. Attachment for scavenging tubing
what does APL valve stand for?
adjustable pressure limiting valve
identify the components of this breathing system and identify the type
Circle (clockwise from right) 1. unidirectional valves - ensure gas flow in one direction 2. attachment to common gas outlet of anaesthetic machine 3. soda lime canister 4. breathing system tubing 5. attachment for scavenging tubing 6. APL limiting valve 7. connection to ET tube/mask 8. reservoir bag
what is the role of soda lime in circle breathing system?
absorbs CO2
what is the approximate value used to calculate tidal volume?
10ml/kg
what size should the reservoir bag on a breathing system be?
3-6x tidal volume
what sizes of reservoir bag are available?
0.5, 1, 2 and 3 litre (larger are available if needed e.g. horse)
why must the reservoir bag be checked before each anaesthetic?
as they perish over time
what does the APL bag attach to?
scavenging system
identify this circuit and it’s weight bracket and circuit factor
Ayres T-Piece
less than 10kg - preferably less than 7.5kg
2-3
identify this circuit, it’s weight bracket and circuit factor
Bain
8-10kg with valve (smaller without valve for smaller animals)
2-3
identify this circuit, it’s weight bracket and circuit factor
Lack (standard)
over 10kg
1
identify this circuit, it’s weight bracket and circuit factor
Mini Lack
more than 1kg
1
identify this circuit, it’s weight bracket and circuit factor
Circle
varies - can have a circuit suitable for any size
not applicable
Guess this capnography trace
normal!
alpha and beta angles less than 90
inspired baseline is 0
guess this capnography trace
cardiac osscilations
normal - particularly in large chested dogs.
caused by pulmonary artery pulsations which affect inspiration - should match HR trace
Guess the capnography trace
leaky ET tube
small complexes and not the correct shape. EtCO2 is also reduced
CO2 is leaking around ET tube and not through sample line
guess the capnography trace
Brochospasm (asthma, anaphylaxis, obstruction)
shark fin
increase in airway resistance causing prolonged attempts to exhale and steep inspiration. Lungs are not emptying properly
guess the capnography trace
bucking
patient on IPPV has neuromuscular blocking agents wearing off and muscle function return. Own muscles are trying to breathe against ventilator
guess the capnography trace
rebreathing of CO2
waseform never reaches baseline 0
INCO2 is 8 and shoudl be 0
what heart arrhythmia is shown on this trace?
ventricular fibrilation
what is the arrhythmia shown on this trace?
1st degree block
what arrhythmia is occuring in this trace?
Mobitz second degree heart block
identify the arrhythmia in this trace
3rd degree block
identify this arrhythmia
ventricular tachycardia
what is the name of this arrhythmia?
ventricular premature complex (VPC)
what animal is this trace from?
horse
