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
should the APL valve be open or closed?
open at all times - can be fatal if left closed
why does resistance within a breathing system matter?
results in hypoventilation - so increased CO2 - and increases work of breathing
what can resistance of a breathing system be influenced by?
tubing and valves (unidirectional and APL)
what effect does an increase in radius have on resistance?
2 x increase in radius will lead to 16 x less resistance
what effect does an increase in length of breathing circuit have on resistance?
2 x increase in length leads to a 2 x increase in resistance
what are the 2 types of breathing system tubing?
coaxial and parallel
describe coaxial breathing system tubing
one tube is inside another
describe parallel breathing system
2 tubes are side by side
what is the resistance like in parallel configurations of breathing systems?
less than coaxial
what is a negative about parallel breathing system configurations?
may increase drug - pull on the ET tube
what is it important to be aware of with coaxial breathing systems?
inner hose disconnection
what is a potential benefit of coaxial breathing system configuration over parallel systems?
warming of inspired air is possible (although may not have clinical impact)
what is the role of soda lime?
absorbs CO2
what type of reaction is the absorption of CO2 by soda lime?
exothermic
what are the products of the absorption of CO2 by soda lime?
water and heat
how is exhaustion of soda lime in a circle circuit indicated?
dye changes colour
what is found within soda lime?
94% calcium hydroxide (Ca(OH)2)
5% sodium hydroxide (NaOH), silica and dye
how much CO2 can one kg of soda lime absorb?
120L CO2
why must gloves be worn when changing soda lime?
it is caustic
what are the 2 types of breathing system?
Non-rebreathing systems
rebreathing systems
how do non-rebreathing systems remove expired CO2?
fresh gas flow
how do rebreathing systems remove expired carbon dioxide?
soda lime
give 3 examples of non-rebreathing systems
T-Piece
Bain
Lack
give an example of a rebreathing system
Circle
which type of breathing system requires a higher fresh gas flow?
non-rebreathing
what are the issues with higher fresh gas flow on non-rebreathing systems?
increased pollution risk
more heat and moisture lost from patient
more expensive to run
what are 3 main benefits of non-rebreathing systems?
inspired agent should be the same as that on the vapouriser
low resistance and lightweight
some suitable for IPPV
cheap to purchase
what non-rebreathing systems are suitable for IPPV?
T-Piece and Bain
what are the benefits of lower fresh gas flow?
lower pollution risk/environmental impact
heat and moisture retained by soda lime
less expensive to run
what are the disadvantages of rebreathing circuits?
slow changes in inspired anaesthetic agent concentration
higher resistance
what should be done if a rapid increase in volatile agent is required by a patient on a rebreathing system?
increased fresh gas flow
can rebreathing systems be used for IPPV?
yes
how is fresh gas flow calculated in non-rebreathing systems?
fresh gas flow = minute volume x circuit factor
what units is fresh gas flow measured in?
ml/kg/min
what value can be used for a minute volume calculation if you don’t know the respiratory rate or if the animal is panting?
200ml/kg/min
what is a circuit factor?
the amount by which the calculated tidal volume of the patient is multiplied by in order to administer the correct amount of gas. Each type of circuit has a different circuit factor
how is fresh gas flow calculated in rebreathing systems?
minimum fresh gas flow = metabolic oxygen consumption
what is the minimum fresh gas flow form large animals?
5ml/kg
what is the minimum fresh gas flow for small animals?
10ml/kg
what is required at low flows on a rebreathing system?
accurate flow meters and vapouriser as the closer the flow is to these values the lower the margin for error
in practice how is fresh gas flow managed on a rebreathing circuit?
high FGF initially and the reduced to 1L/min in animals up to 100kg
what body weight is the Ayres T-Piece used for?
up to 10kg but preferably less than 7.5kg
what is the calculation for fresh gas flow for Ayres T-piece?
FGF = minute volume x 2-3
can Ayres T-Piece be used for IPPV?
yes
why is Ayres T-Piece good for small patients?
low resistance and dead space
what causes modest drag in an Ayres T-Piece breathing system?
2 parallel tubes
what has made Ayres T-Piece easier to scavenge?
version with APL valve which has an attachment for scavenge
what animals is the Ayres T-Piece used for?
cats and exotics
what weight of animals is the Bain circuit used for?
8-20kg with valve (smaller bain without valve may be suitable for smaller animals)
how is FGF calculated for a Bain circuit?
FGF = minute volume x 2-3
what are the benefits of a Bain circuit?
can be used for IPPV
low drag and dead space
easy to scavenge
what are the issues with a Bain circuit?
inner tube can become disconnected (coaxial configuration)
how can the integrity of a breathing circuit be tested?
connect to common gas outlet, occlude patient end of tubing. Close APL and allow reservoir bag to fill, listen for leaks. open APL valve to release pressure
how can the inner tubing of a Bain circuit be tested?
using 15ml syringe plunger occlude only inner tube. Place FGF on 4l/min. Should trigger pressure release valve on bakc bar
what patients are most suited to the Lack circuit?
patients >10kg (mini versions available)
what is the drag, resistance and dead space like in a Lack circuit?
moderate
what is the fresh gas calculation for the Lack?
minute volume x 1
is a Lack circuit suitable for IPPV?
no - occasional breaths are ok, can cause rebreathing
why is a Lack circuit not suitable for IPPV?
can cause rebreathing
what sizes of circle circuit are available?
variety - human adult >20kg small animal systems >15kg smaller ones are available for cats and dogs with paediatric tubing large animal versions
what parts of a circle circuit contribute to resistance?
unidirectional valves, soda lime canister and APL valve
what is the FGF of circle circuits set as?
more than metabolic oxygen requirement (1l/min for animals under 100kg, 0.5-1l/min for animals over 100kg)
what factors must be considered when choosing a breathing system for a case?
size of animal valve position and IPPV requirement ease of scavenging cleaning and sterilisation use of nitrous oxide heat an moisture retention
what are the signs of APL valve being accidentally left closed?
reservoir bag distends reduction in thoracic movements possible leaking around ET tube cuff tachycardia hypoxia
why are thoracic movements reduced if the APL valve is left closed?
animal struggles to breathe against pressure created in circuit
what conditions can be caused by the APL valve being left closed?
pneumothorax
pneumomediastinum
rupture of lung tissue or trachea
potentially fatal
how is accidental closure of the APL valve prevented?
systematic approach to system checks and checks when attaching to new system
how can excessive resistance in the breathing system be recognised?
altered RR (low or occasionally fast)
decreased tidal volume
hypoventilation and hypercapnia - increased end-tidal CO2
hypoxia
altered respiratory pattern (e.g. paradoxical breathing)
what can reduced alveolar ventilation due to excessive resistance in the breathing system lead to?
light plane of anaesthesia as impact on uptake of VA
what may apparatus dead space be formed from?
integral part of breathing system (e.g. ET tube connector) or excessively long ET tube protruding from mouth
what is the effect of increasing dead space to tidal volume ratio?
increases PaCO2
increases work of breathing
why does increasing dead space to tidal volume ratio increase the work of breathing in small animals?
minute volume needs to increase to maintain PaCO2 at normal levels
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
what is meant by the post op period after anaesthesia?
procedure is finished and the patient now needs to regain consciousness and start their recovery
what are the 2 key steps involved in getting the patient into recovery?
preparing for end of anaesthesia
end of anaesthesia
what should be done when preparing for the end of anaesthesia?
reduce volatile agent or IV agent (whatever is keeping the patient asleep)
turn up to 100% oxygen if using nitrous oxide
how can you tell when you need to prepare for the end of anaesthesia?
watching the procedure to see when the vet is nearly finished (e.g. skin closure nearly done)
why is turning up to 100% on preparation for the end of anaesthesia necessary if nitrous oxide has been used?
counteracts hypoxia
what should you do at the end of anaesthesia?
turn off all anaesthetics
ensure analgesia is in place
describe the ideal recovery environment
safe and secure ideally purpose built well ventilated warm accessible and easy to observe patients close proximity to clinical supplies (e.g. oxygen, catheters, swabs, CPR kit) and staff
why is the ideal recovery area well ventilated?
animals will be exhaling anaesthetic gases to remove them from the body
what are the 4 key types of airway management devices used in veterinary practices?
SGAD (V Gel)
ET Tube
LMA
face mask
what should be done in recovery in all species if the patient has an intubated trachea?
loosen/untie the ties on ET tube ready to remove (extubation)
when should the ties on an ET tube be undone in a recovering patient?
personal preference situation dependent (not if you are just about to move the patient)
when should the cuff of a cuffed ET tube be deflated during recovery?
close to extubation (ideally 1 min before!), not when you turn off volatile agent
why should the cuff of a cuffed ET tube be deflated close to extubation?
prevention of aspiration and improved airway control
what are the signs that show that dogs and rabbits should be extubated?
signs that laryngeal reflexes are returning (e.g. swallowing)
other reflexes returning and/or spontaneous movement
when should cats be extubated?
when showing earlier reflexes (e.g. ear flick and blink) and before swallowing returns
why must cats be extubated before swallowing returns?
have very sensitive larynxes and there is a danger of laryngospasm if you wait for swallowing
when should horses be extubated?
respiration rate is a good guide as laryngeal reflexes are weak
how should the tube be removed once you have judged it is time?
smoothly remove tube without damaging the airway (remember ET tube shape) - don’t wriggle the tube!
what happens if the ET tube is removed too early?
the patient has an unsupported airway
what should you do if the tube has been removed too early?
maybe provide supplemental oxygen (flow-by)
have laryngoscope and ET tube ready just in case
what may happen if the tube is removed too late?
patient may bite tube/damage airway/get distressed/develop laryngospasm (cats)
when may late extubation be necessary?
in patients at high risk of airway obstruction (e.g. BOAS dogs after airway surgery)
what must you do if performing late extubation on patients?
monitor carefully
can late extubation be performed on cats?
no - due to risk of laryngospasm
is late extubation well tolerated?
mostly in patients that require it due to the fact they live with breathing difficulties - not all though!
what should be done with the patients tongue around the time of extubation?
pull out to the side of mouth so that it doesn’t obstruct the airway
what can be done with the mouth/tongue before extubation to make the patient more comfortable?
wet with a damp swab
why may you want to gently tug the patients tongue as it is beginning to recover more?
sometimes seem to have their tongue stuck out of their mouth - a gentle tug may help them to regain function and pull it back in!
following extubation what are the stages of recovery?
lift head
assume sternal recumbancy
stand
full recovery with no signs of sedation/ataxia
what must be monitored on recovery of all patients no matter their ASA grade?
Temperature
Pulse
Respiration
quality of recovery
pain/analgesia
what should the frequency of temperature measurement in the post op period depend on?
individual case - more if attempting t address hypo/hyperthermia
less if uncomplicated recovery
what are the effects of hypothermia on the recovering patient?
bradycardia and cardiac arrhythmias impaired coagulation and wound healing prolonged duration of action of drugs so slower recovery from anaesthesia decreased renal plasma flow decreased oxygen delivery to tissues shivering may increase o2 requirement
at what temperatures can atrial fibrillation be caused?
30 degrees C
at what body temperatures can ventricular fibrillation be caused?
24-28 degrees C
why does hypothermia lead to prolonged duration of action of drugs and so slower recovery from anaesthesia?
slows metabolism
how can hypothermia during and after anaesthetic be minimised?
warm from time of premed - particularly IM
warm throughout perioperative period
use heating devices
ensure warm environmental temperature
how can an animal be warmed throughout the peri-operative period?
insulation
warmed fluids
HME or rebreathing system
perform skin prep/clipping before anaesthesia to reduce anaesthetic time
what is a HME?
heat and moisture exchanger put between ET tube and breathing system to raise heat and humidity of inspired air
what can cause hyperthermia in the anaesthetised/recovering patient?
decreased heat loss
excessive external heat
increased metabolic production of heat due to underlying process
what are the physiological effects of hyperthermia?
increased basal metabolic rate
increased oxygen requirement
parenchymal cell damage
by how much does basal metabolic rate increase for every degree C above normal temperature?
13%
what effect can a temperature of >41 degrees C have on the body?
irreversible brain damage
what effect can a temperature of >43 degrees C have on the body?
death
if using wheat bags what must happen to ensure the patient is not burned?
wrapped in a towel and never in direct contact with the patient
when checking pulse what are you assessing?
circulation
what pulses are best to check quality of circulation?
peripheral
what else should be checked as a measure of circulation?
MM
CRT
what equipment may be used to assess circulation?
pulse ox is desirable but usually impractical after a certain point in recovery!
auscultate chest with stethoscope
ECG if required
what types of obstruction must be checked for to ensure a patent airway?
oral obstruction
anatomical obstruction
what may an oral airway obstruction be caused by?
mouth packs
saliva
vomit
what may an anatomical obstruction be caused by?
head stuck in corner of the cage and neck kinked
when should an animal be placed in its kennel?
only once it is able to lift it’s head
what can be done with a patient if concerned about the risk of inhalation of saliva/blood/vomit?
patient placed in head down position
what must you do if your patient is in head down position with the kennel door open?
must be observed at all times
what must be removed from the kennel while the patient is recovering?
water bowl - semi conscious patient may drown in it
what must be observed when looking at a patients respiration?
that they are breathing!
resp rate in breaths per minute
note pattern
auscultate
what should be noted about the patients respiratory pattern?
deep vs shallow
thoracic or abdominal
what should be done if you are concerned about a patients breathing?
provision of oxygen supplementation
what are the main types of oxygen supplementation?
oxygen cage/tent
face mask
nasal oxygen
flow by
what animals is an oxygen tent suitable for?
smaller patients only
what are the issues with face mask and nasal oxygen to provide oxygen supplementation?
may not be tolerated and can make respiration worse if patient is stressed by them
what is the ideal recovery?
calm and stress free for all
what behavior is often seen in recovery?
excitement
what should be done if the patient is excitable on recovery?
monitor and observe - potentially resedate
what must be provided to ensure patient cannot injure himself or staff during recovery?
suitable cage/box and remove obstructions
in what animals is a controlled recovery essential to prevent serious injury?
horses
what is the ideal way of measuring pain?
recognised pain scoring system
what should additional analgesics be given based on?
patients pain score and not based on what time they last had a pain killer
what behaviours may indicate pain in animals?
inappetance reluctance to walk/move/jump/stand difficulty in mobility vocalisation panting lip-smacking yawning aggression sleeping more reacting badly to being touched
why do some animals not exhibit many pain behaviours at all?
prey vs predator - prey animals cannot afford to be seen as weak
what are the main physiological signs of pain?
increased: HR, RR, temp and BP
what are the subjective pain assessment tools?
simple descriptive scales
numerical rating scales
visual analogue scales
what are the more precise pain assessment tools for animals?
composite scales
grimace scales
behavioral assessment
why are composite pain scales preferable to more subjective measurements?
have a prescribed point for analgesia
less subjective!
when are grimace scales useful?
in patients who don’t show pain in traditional ways (e.g. rabbits)
how should assessment using a grimace scale be done?
over a short period of time and ideally remotely
what do grimace scales look at?
pain face - eye and ear position are recognised as good indicators of pain in some species
what other area must be considered as well as pain when assessing patient comfort?
full bladder cold too hot wet bedding tight stitches clipper rash need to defecate fear/anxiety
what must be done with IV catheters during recovery?
flushed, patent with fluids flowing
properly covered and suitably padded
what must be done when removing IV catheters?
apply pressure to the area to ensure haematoma doesn’t form
what should be checked before recovering the animal?
wound checked and dressing/creams applied if needed
check consent form for any additional procedures
check that nothing is swelling due to over tight dressings
what may be needed if the patient is interfering with the wound?
extra dressings/collar/suit
when checking the surgical wound what are you looking for?
bleeding or swelling
what are the key considerations when nursing the recovering patient?
clean, dry, warm and quiet
toilet needs met
water and food when appropriate
TLC
when should animals be fed post op?
when awake/able to stand and swallow except for specific surgeries
what procedures may mean that patients cannot be fed once they are awake and able to stand?
GI surgery (controlled feeding)
Sedation /CRIs
follow up imaging needed
what type of food should be given post op?
bland, soft food
what meal size and frequency is ideal post op?
little and often
what may be necessary when feeding small mammals in recovery?
assisted feeding
why is it so crucial that rabbits eat soon after surgery?
at risk of ilius and gut stasis
where should post op data be recorded?
specific continuation sheet (hospital record) or on the back of anaesthetic record card
why should all post op care be noted down?
in case of an adverse event can demonstrate that care was provided
why must a general anaesthesia record be completed for every patient?
legal document
when should each round of parameter checks be completed?
minimum of 5 minutes
what parameters are measured during general anaesthesia monitoring?
HR BP resp rate temperature pulse ox drug doses (inc. O2 and volatile agent)
when should anaesthetic monitoring take place?
from time of premed to time of recovery
what other information, aside from monitoring record should be included on the anaesthetic record?
animal details
staff involved
where should anaesthetic records be stored?
animal file
who assigned guidelines for assessing depth of anaesthesia?
Guedel
why is Guedel’s work on anaesthesia planes not totally reliable with veterinary patients?
rare that only inhalant drugs are given. Balanced anaesthetic technique will influence reflex and autonomic responses
what parameters are relied upon when monitoring patients under a balanced anaesthetic technique?
physiological parameters
how many stages of anaesthesia are there?
4
name the stages of anaesthesia
stage 1-4
which anaesthesia stage is divided into 3 planes?
stage 3
what are the names of the 3 planes of stage 3 of anaesthesia?
plane 1, 2 and 3
when does stage 1 of anaesthesia occur?
begins at time of induction and lasts until unconsciousness is present
what are the physiological effects seen during stage 1 of anaesthesia?
pulse and resp rates are often elevated, breath holding may occur and pupils may dilate
when does stage 2 of anaesthesia occur?
lasts from onset of unconsciousness until rhythmic breathing is present
what reflexes are present during stage 2 of anaesthesia?
all cranial nerve reflexes are present and may be hyperactive
describe eye position in stage 2 of anaesthesia
eye may appear wide and open with pupil dilated - the eye will soon rotate to ventromedial position
describe signs of plane 1 of stage 3 of anaesthesia
respiration becomes regular and deep, spontaneous limb movement is absent but pinch reflex may be brisk. Nystagmus, if present, will start to slow and disappear
describe eye position during plane 1 of stage 3 of anaesthesia
eyeball is now ventromedial, opening the eye will show the sclera
what is plane 1 of stage 3 of anaesthesia suitable for?
minor procedures (e.g. abscess lancing and skin suturing)
describe plane 2 of stage 3 of anaesthesia
palpebral reflex is sluggish or absent although corneal reflexes remain.
Muscles appear relaxed, pedal reflex begins to go
Tidal volume may decrease as resp rate settles.
HR and BP may be slightly reduced
describe eye position during plane 2 of stage 3 of anaesthesia
eye position is ventromedial and the eyelids my be partially seperated
what procedures is plane 2 of stage 3 of anaesthesia adequate for?
most surgical procedures
describe plane 3 of stage 3 of anaesthesia
pedal reflex is lost
abdominal muscles are relaxed
HR and BP may be low
what is the pedal reflex?
pinching between patients toes to see when they withdraw their foot and the speed at which they do
describe the eye position of plane 3 of stage 3 of anaesthesia?
eyeball becomes central and eyelids begin to open
pupillary diameter increases
describe physiological signs of stage 4 of anaesthesia
progressive respiratory failure
pulse may be rapid or very slow and become inpalpable
CRT becomes prolongued
sometimes may see accessory respiratory muscle activity - twitching in the throat (can be confused with light plane of anaesthesia)
describe the eye position during stage 4 of anaesthesia
central eye with no palpebral reflex
what is happening during stage 4 of anaesthesia?
anaesthetic overdose
why should an anaesthetic be monitored?
volatile agents are used which have a profound effect on the patient
it is a legal requirement
there can be quick changes in the animals equipment
what can be monitored during anaesthesia?
depth of anaesthesia CVS respiratory system inhalent/drug administration body temperature urine output blood glucose blood gases neuromuscular function
why should inhalant/drug admin be monitored?
avoid dose dependent effects
what parameters can be monitored during general anaesthetic with minimal equipment?
temperature ventilation pattern resp rate pulse quality heart rate thoracic auscultation mucous membranes CRT eye position
what parameters can be monitored during anaesthesia but require more specialist equipment?
pulse ox capnography spirometry ECG BP
what is an oesophageal stethoscope used for?
listening to heart and breath sounds in the anaesthetised animal
where should the oesophageal stethoscope be placed?
via the oesophagus to the level of the heart base
how should an oesophageal stethoscope be placed?
palpate apex beat and measure stethoscope against the animals lateral neck and thorax, listen as you pass the stethoscope into the oesophagus and stop once you can hear heart sounds
describe correct eye position in an adequate plane of anaesthesia
ventromedial position with absent palpebral reflex
describe eye position in an light plane of anaesthesia
central with palpebral reflex
describe eye position in a deep plane of anaesthesia
central with no palpebral reflex
what must be monitored alongside anaesthesia?
patient reaction to any drugs given - side effects or adverse response
describe the depth of this plane of anaesthesia:
increased HR
increased resp rate
mucous membranes pink
CRT - brisk
central eye position with slight palpebral reflex
too light
Describe the depth of this plane of anaesthesia:
steady HR
slightly reduced resp rate
mucous membranes pink
CRT <2 secs
ventromedially rotated eye position with no palpebral reflex
adequate
describe the depth of this plane of anaesthesia:
steady HR
slightly reduced resp rate
mucous membranes pink/pale pink
CRT 2-3 seconds
central eye position with no palpebral reflex
too deep
what are the key tips for good anaesthetic monitoring?
focus no distractions treat patients as if they were yours make the recording sheet legible ask for help
what body system does blood pressure indicate the function of?
CVS and perfusion
what is arterial blood pressure a measure of?
the pressure exerted by blood on the walls of the blood vessels
what is arterial blood pressure an indirect indicator of?
blood flow
why is it so critical that blood pressure is monitored in the anaesthetised patient?
most drugs used cause suppression of the CVS, respiration and BP leading to hypotension
what are the 2 key methods of blood pressure measurement?
indirect / non-invasive (NIBP)
direct / invasive (IBP)
what are the 2 methods of indirect / non-invasive blood pressure measurement?
doppler
oscillometric
what is involved in direct / invasive measurement of blood pressure?
placement of an arterial line catheter
what are the advantages of direct blood pressure measurement?
accurate
reliable
beat to beat info
what are the disadvantages of direct blood pressure measurement?
invasive
expensive
requires experience to place
what are the advantages of indirect / non-invasive blood pressure measurement?
non-invasive
easy
can detect trends
cheap
what are the disadvantages of indirect blood pressure measurement?
may be less reliable and accurate than arterial line
slower to gain a result
what animals is doppler indirect arterial blood pressure measurement best?
cats
in what states is a doppler able to detect arterial BP?
pulse flow can be detected in low flow states
what are the benefits of doppler technique for indirect measurement of BP?
inexpensive
efficient
quick results
what blood pressure can be measured with a doppler?
systolic only
what are the disadvantages of oscillometric BP measurement compared to doppler?
less reliable
interference caused by movement of animals (harder when conscious)
not as effective in small animals (e.g. cats)
more expensive
what blood pressure types can be detected by oscillometric measurement?
systolic
diastolic
mean
what equipment is needed for a doppler BP measurement?
Doppler unit (microphone) Sphygmomanometer headphones selection of cuffs gel spirit clippers
what is systolic blood pressure the measure of?
the force the heart exerts on the walls of the arteries
what is diastolic blood pressure the measure of?
the pressure in the arteries when the heart is between contractions
what is mean arterial blood pressure the measure of?
the intravascular pressure in the vessel during one complete cardiac cycle
describe the basic principle of how a doppler machine works?
doppler flow meters detect blood flow and emit an ultrasonic signal. An auditory signal is produced by a frequency shift of underlying red blood cells. An inflatable cuff is placed around the limb and inflated which occludes the artery. This will cause the noise to stop. The cuff is then deflated until the sound returns and blood pressure is read.
what is the ideal cuff width for blood pressure monitoring?
40% of the limb circumference
what cuff should you choose if the calculated width falls between 2 sizes?
the larger of the two
what will happen to the BP reading if the cuff is too small?
result will be artificially high
what will happen to the BP reading if the cuff chosen is too big?
the result will be artificially low
what are the benefits of oscillometric blood pressure monitoring?
automated convenient (esp. during anaesthesia)
which of the blood pressure measurements is the least reliable on oscillometric BP measurement?
diastolic
what is required to perform direct arterial pressure monitoring?
arterial catheter placement
why must the use of direct arterial blood pressure be justified?
it is invasive and their is high risk of infection
what is the ‘ideal’ patient for direct arterial blood pressure monitoring?
sick
require haemodynamic support
undergoing major procedures
why must placement of an arterial line be aseptic?
high risk of infection
what additional equipment may be required when placing an arterial line?
inco-sheet as bleeding is likely
why must a patient with an arterial BP monitoring line in be closely monitored?
if interfered with infection could be introduced
if removed there will be heavy bleeding
what should be done to arterial lines to ensure they are not confused with IV lines?
clearly labelled as some drugs cannot be safely administered into an artery
what must happen when an arterial line is removed?
pressure bandage applied for at least 40 mins to prevent bleeding
what is the most common artery used for arterial blood pressure monitoring?
metatarsal or dorsal pedal artery
why is the metatarsal /dorsal pedal artery the best choice for arterial monitoring?
easy to secure in place
easier to maintain for post-op monitoring
less risk of large haematoma
how does direct arterial line monitoring measure blood pressure?
electronic system attached to fluid filled tubing system
the catheter detects pressure waves in the arterial system, this transfers pressure waves to the fluid common in the tubing system and so to the diaphragm of the electronic transducer. This is converted to an electric signal and shown of the monitor
how must the transducer of the direct BP monitoring system be set up?
placed at heart level (referenced)
set at atmospheric pressure at the zero reference point
how can the accuracy of direct arterial blood pressure monitoring be improved?
reduction of factors which alter the mechanical waveform and so the reading e.g. air bubbles or interference
what is the aim of blood pressure monitoring during anaesthesia?
maintain adequate BP to to maintain tissue oxygenatio
what is mean arterial blood pressure the combination of?
cardiac output and peripheral vascular resistance
what is the driving force behind tissue oxygenation?
blood pressure
what are the main effects of anaesthesia on blood pressure?
causes vasodilation due to drugs and volatile gases used - this has a negative impact on BP and leads to hypotension
what is the ideal systolic blood pressure of anaesthetised patients?
90 mmHg
what should be done if systolic blood pressure is low?
identify underlying cause
reduce volatile agent
consider concurrent use of local blocks and topping up analgesia
what should be done if the patient has become bradycardic due to low blood pressure?
manage bradycardia
consider fluids
consider drug therapy (anticholinergics/vasopressors/beta 1 adrenergic agonists)
what are the 3 main ways of maintaining anaesthesia?
gaseous
injection
TIVA (total intravenous anaesthesia)
what is the most common method of anaesthesia maintenance?
gaseous
what is a volatile anaesthetic agent?
a liquid that at room temperature changes into a vapour and when inhaled is capable of producing general anaesthetic
what does a higher MAC mean?
it is less potent - more is required to have an effect
what can lower MAC?
use of drugs in balanced anaesthesia
what is MC sparing?
anything that will lower MAC
what can reduce MAC?
hypothermia hypoxaemia hypercapnia drugs - sedative or injectable agents analgesics pregnancy old age hypotension
what is the blood solubility of sevoflurane?
0.69 - quick changes in depth, recovery and indction
what is the blood solubility of isoflurane?
1.4 - fairly rapid induction and recovery
what is the effect of lower blood solubility on anaesthetic gases?
can only go to target organ rather than round the body - effect is quicker and so is recovery
does sevoflurane or isoflurane have a lower blood solubility?
sevoflurane
why does reduced cardiac output lead to better uptake of anaesthetic gases?
increases alveolar ventilation as blood is moving ‘slower’
what proportion of isoflurane metabolism is hepatic?
1%
what proportion of sevoflurane metabolism is hepatic?
3%
what is the main route of elimination of anaesthetic gases?
exhalation
what is the MAC of isoflurane?
1.4-1.6
is isoflurane well tolerated for induction?
no - irritant to MM
what is a common side effect of isoflurane?
peripheral vasodilation leading to hypotension
does isoflurane provide analgesia?
no
what is the MAC of sevoflurane?
2.1-2.6
is sevoflurane irritant to MM?
no
does sevoflurane provide analgesia?
poor
what is produced when sevoflurane degrades in soda lime?
compound A produced
what is compound A linked to?
nephritis in rats
how is nitrous administered?
gas
what is the MAC of nitrous?
> 100%
what is nitrous used as?
supplement to anaesthesia
does nitrous have good anaesthetic properties?
yes
are their cardiopulmonary effects of nitrous?
minimal
why is there rapid uptake and elimination of nitrous?
it is insoluble
what effects on the lungs can nitrous have?
second gas effect
diffusion hypoxia
explain the second gas effect
high level of plasma solubility of NO2 leads to rapid diffusion into the blood stream. This increases the concentration of VA and O2 in the alveoli and so increases speed of diffusion of these gases into the blood stream
explain diffusion hypoxia
at the end of NO2 supply to patient there is rapid diffusion of nitrous back into alveoli which dilutes VA and oxygen within alveoli and reduces diffusion into the patient
what are the side effects in animals of volatile agents?
cerebral effects
CV effects
respiratory effects
what are the cerebral effects of volatile agents?
reduced cerebral metabolism so reduced blood flow and reduced oxygen consumption
what are the cardiovascular effects of volatile agents?
does dependent depression of output
reduction in peripheral resistance and vascular tone due to a reduction in myocardial contractility and vasodilation
what are the personnel effects of volatile agents?
mutagenic and teratogenic
reduced fertility
renal and hepatic disease
what steps must be taken to ensure safe use of volatile agents?
avoid personnel exposure
avoid gas induction
place ET tube and inflate cuff before turning on vapouriser
leave patient connected to breathing system for as long as possible
ensure adequate scavenging
ensure machines are turned off after use
recover patients in well ventilated area
train staff to know what to do if there is a spillage
what are the problems with using a facemask to deliver volatile agents?
atmospheric pollution potential for airway obstruction/aspiration IPPV may be difficult monitoring can be difficult hard to secure labour intensive
how should volatile agent be administered?
titrate to effect to allow for individual differences and patient own parameters
how can IM injections be used to maintain anaesthesia?
those used for induction may be sufficient (e.g. triples)
give repeated injections
what are the issues with using IM maintenance of anaesthesia?
difficult to control depth - slow onset and unpredictable
limited access
limited range of drugs
what is preferable to IM anaesthesia?
IV
what does IV anaesthesia require?
secure V access
what are the benefits of IV injections to maintain anaesthesia?
can give repeat
non-painful
what are the downsides to IV injection maintenance of anaesthesia?
can result in an unstable plane of anaesthesia when using bolus techniques
can get cumulative effects of some drugs (species differences)
how are IV anaesthetic maintenance drugs eliminated?
metabolism
what is TIVA?
the use of a continuous rate of drug to maintain anaesthesia - no boluses
when would TIVA maintenance of anaesthesia be ideal?
lung surgery
what is essential to provide TIVA?
IV access
what is a possible effect on recovery from using TIVA?
prolonged recovery if prolonged infusion
why is technical skill required for TIVA?
tricky calculations
how is TIVA often delivered?
syringe drive/pump
how do rabbits most often have anaesthetic maintained?
gas or injectable
do rabbits often receive TIVA?
uncommon
what are the advantages of inhalational anaesthetics?
easy to administer/calculate
suitable for most patients
easy to adjust depth
what are the disadvantages of inhalational anaesthetics?
requires specialist equipment
has impact on BP through vasodilation (hypotension)
personnel risks
what are the advantages of injectable anaesthesia?
available in all settings
can be administered by a nurse
provides good level of sedation
what are the disadvantages of injectable anaesthetics?
careful dosing needed
limited choice of drugs
not so easy to to change depth quickly/if at all
what is considered when deciding what maintenance technique to use?
species behaviour procedure facilities expertise budget
what shoudl be avoided when moving the patient?
twisting of ET tube / breathing system when moving
accidental disconnection or extubation
how can airway maintenance issues be identified?
check equipment
watch patient (particularly the thorax)
capnography
look for changes in parameters
why is positioning of the patient under anaesthesia so important?
prevent muscle or nerve damage
prevent post-op pain
optimise ventilation
how can eyes be protected during anaesthesia?
occular lubricant
what can be used to aid correct positioning?
bedding / padding / foam wedges
what are the 4 main whys through which heat can be lost?
convection
conduction
radiation
evapouration
how is heat lost through convection?
the loss of heat to cool air surrounding the body
what can make heat loss through convection worse?
low ambient temperature or drafts
how is heat lost through conduction?
loss on body heat to surfaces that are in contact (e.g. kennel floor or theatre table)
how is heat lost through radiation?
loss of body heat to structures not in contact with the patient
how is heat lost through evaporation?
from moisture evaporation (e.g. surgical scrub/alcohol or open body cavity)
what are the 2 ways which anaesthesia can affect hypothermia?
by increasing blood flow from core to periphery
by interfering with the body’s thermoregulatory mechamisms and by reducing metabolic rate and heat generated
what is the effect of anaesthesia increasing blood flow from core to periphery?
leads to increased heat loss and a fall in core temperature
what is the physiological impact of hypothermia?
CNS depression hypotension bradycardia hypoventilation decreased basal metabolic rate decreased urine output
what are the main risk factors for heat loss/hypothermia?
high surface area to body weight ratio little body fat thin hair large area of coat loss large amount of internal tissue exposed insufflation of cold air (e.g. during endoscopy) extremes of age ectothermic animals (e.g. reptiles)
what can be done to reduce the risk of hypothermia?
minimal anaesthetic time minimal wetting of fur (e.g. scrub or ultrasound gel) maintain high ambient temp use heat an moisture exchangers on breathing systems use appropriate breathing systems warmed fluids for IVFT and lavage kep patient warm from premed onwards use insulating materials
what are some key sources of patient warming?
blankets/towels/bedding incubators heat mats microwave warming bags hot water bottles hot hands forced air warming systems (e.g. bair hugger) heat lamps warm water enema/bladder lavage (last resort)
what body systems can capnography be used to monitor?
pulmonary and CVS
what 4 pieces of information can be gained from capnography?
inspired CO2 - number
expired CO2 - number
respiratory rate
capnograph - wave form
what are the 2 types of capnography devices?
multiparameter - part of a larger machine
handheld
what does EtCO2 show?
how much CO2 patient is exhaling
what does INCO2 show?
how much CO2 patient is inhaling - should be 0
how should capnograpy be set up?
check machine is plugged in/batteries are ok
untangle leads
select connector (sidestream or main stream)
ensure connector/sample line are in good order
attach connector to breathing system ready to use
turn on machine
capnogram will show once patient breathes
what are the 2 types of capnography?
sidestream
mainstream
how does sidestream capnography work?
connector is attached between ET tube and breathing system with a sample line coming off - patient breathes in fresh gas and exhales waste gases. Small amount of air is removed via the connector and transmitted to machine through sample line (e.g. Torbridge system)
what are the advantages of side stream capnography?
cheaper
less likely to break
easy to replace if broken
what are the disadvantages of sidestream capnography?
slight time delay in results (not quite real time)
takes some of the FGF requirement from the patient so FGF may need to be raised particularly when using low flow
sample line is easily damaged and needs changing regularly
how much FGF may be taken by a sidestream capnography sample line?
150ml per sample
does mainstream capnography require a sample line?
no - just a connector between ET tube and breathing system
how does mainstream capnography work?
gases are analysed within connector which they pass through out of the patient. Infra red light is shone through the gas stream onto a sensor on the other side. CO2 absorbs infra red so the more there is the less infra red will reach the sensor. The result is then displayed as a number on the multiparameter
why is infra red light used on mainstream capnography?
CO2 absorbs infra red radiation and so reduced levels will be detected by the sensor when CO2 is present
what are the advantages of mainstream capnography?
real time results
no need for sample line so there is no FGF requirement
what are the disadvantages of mainstream capnography?
very expensive to buy
can be easily damaged
can add drag to the system
what is sampled by capnographs?
CO2 in both inspired and expired gas
in a healthy patient/correct capnograph trace what should the value of the baseline be?
0
what happens in phase 1 of the capnograph waveform?
shows inspired gases - value should be 0
what happens in phase 2 of the capnograph waveform?
start of expiration - anatomic dead space and gas from bronchioles and alveoli leave the airway
what is the alpha angle of the capnography trace used to measure?
ventilation/perfusion mistmatch
what happens in phase 3 of the capnograph waveform?
alveolar plateau - last bit of alveolar gas is sampled
what is the beta angle used to assess?
rebreathing
what will happen to the beta angle of the capnograph trace if rebreathing is present?
> 90 degree angle
what will happen to the alpha angle of the capnograph trace if a V/Q mismatch is present?
> 90 degree angle
what happens during phase 0 of the capnograph trace?
inspiratory downstroke - marks beginning of inspiration where trace should drop to baseline - 0
what is normal end tidal CO2 (EtCO2) in dogs?
35-45 mmHg
what is normal end tidal CO2 (EtCO2) in cats?
28-35 mmHg
what is normal inspiratory CO2 (INCO2) of all species?
0 - should not be inhaling any CO2
what is the respiration rate of all species that should be shown on the capnography readout?
variable!
what can high EtCO2 be caused by?
hypoventilation
reduced respiratory rate
reduced tidal volume
define tidal volume
the amount of air that moves into or out of the lungs during one respiratory cycle
what is low EtCO2 caused by?
hyperventilation low cardiac output decreased metabolic rate hypothermia PE leak in sample line poor sample technique (dilution) leak in breathing system
why may low cardiac output lead to low EtCO2?
lower amount of CO2 being moved from the respiring tissues to lungs due to reduced blood movement round body
what has an effect on the causes of high INCO2?
type of breathing system used
what can cause high INCO2 in a non-rebreathing system?
too low FGF
too much dead space (e.g. ET tube too long)
what can cause high INCO2 in a rebreathing system?
exhausted absorptive agent - CO2 not being removed
faulty/sticky unidirectional valuves
what are the benefits of canography?
non-invasive easy to set up easy to use very efficacious way of monitory ventilatory ability of patient can give info on cardiac output
what are the limitations of capnography?
increased dead space
requires ET tube/mask (if well fitting)
how can dead space be reduced?
correct size of ET tube and any connectors used
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 is the point of anaesthesia?
take an animal into a state of unconsciousness to perform a required procedure. the animal then regains consciousness without any long term impairment (hopefully)
what approach should be taken when things aren’t going to plan in anaesthesia?
logical
what is SpO2 a measure of?
how much oxygen the blood is carrying as a percentage of the maximum it could carry
will a patient with low SpO2 have cyanotic membranes?
not necessarily
what should the normal SpO2 in an anaesthetised dog or cat breathing 100% O2 be?
98-100%
what is occurring when SpO2 has fallen?
hypoxia/hypoaemia
what value should SpO2 remain above during anaesthesia?
above 95%
at what value is SpO2 concerning?
90%
what is the first thing that should be done if SpO2 isn’t above 95%?
reposition/ moisten tongue to ensure reading is correct
what 3 separate conditions of oxygen contribute to SpO2?
oxygen that is supplied to patient
oxygen transported into lungs
oxygen being delivered to tissues
what is the first thing that must be checked if SpO2 has dropped and the probe doesn’t need repositioning?
do you have control of the airway
what should be done if SpO2 has dropped and oxygen is being supplied by a mask?
check for leaks
may need to intubate
what should be done if SpO2 has dropped and oxygen is not being supplied by a mask or airway device?
straighten neck, pull tongue forward, check mouth and suction if required. Then supply oxygen either via a mask or intubate
what should happen if the patient is not getting oxygen?
should be supplied
what may be causing low SpO2 in the non intubated patient?
may be airway obstruction: anatomical (e.g. in brachycephalic breeds), a condition (e.g. laryngeal mass) or debris such as food or vomit
what method provides complete airway control?
tracheal intubation
what issues with the patient can potentially cause difficult intubation?
laryngeal mass or anatomical issues (e.g. brachycephallic dogs)
how can you prepare for a potentially difficult intubation?
pre-oxygenation with mask prior to attempt to intubate
have all equipment that may be needed to hand before intubation attempt
may need to administer corticosteroids (hydrocortisone)
why may administering corticosteroids help with a potentially difficult intubation?
reduces inflammation
if the patient is intubated and they are attached to the anaesthetic machine what is the next thing that should be checked to try and correct low SpO2?
is oxygen being provided to the patient
how can you check that oxygen is being supplied to the patient?
check pressure gauges on anaesthetic machine to see that pressure is ok
if the pressure is ok on the anaesthetic machine gauges what should be checked next?
flow rate is adequate for the patient and circuit used
what should you do if flow rate is not adequate for the patient and circuit used?
adjust as appropritate
if the pressure is not ok on the anaesthetic machine gauges what should be done?
check cylinder is turned on, whether or not it is empty and that the pipeline is plugged in
what should be done prior to anaesthesia to avoid SpO2 dropping due to equipment issues?
checking of machines and equipment
if oxygen is being supplied correctly what should be checked next?
breathing system and ET tube
what should be checked when looking at the breathing system and ET tube to ascertain why SpO2 is dropped?
is the breathing system correctly attached to the machine and patient
what should be done if the breathing system is not correctly attached to the machine and patient?
correct all connections
what should be done if the breathing system is correctly attached to the machine and patient?
check to see if breathing system is leaking or there is a leak around the ET tube
what should be done if the breathing system is leaking or there is a leak around the ET tube?
fix it or replace it
when can a leak around ET tube cuffs occur even if they have been properly secured?
when patient is moved
is there is a slow leak in the cuff valve
what must be assessed if oxygen is being provided to the patient, the breathing circuit and ET tube cuff are fine but the SpO2 is still low?
is oxygen reaching the patients lungs
what must be assessed about a patients breathing if they are receiving oxygen but SpO2 is low?
are they breathing spontaneously
what should be assessed about a patient who is breathing spontaneously with low SpO2?
is there a normal or abnormal respiration pattern
what should be assessed about a patient who is not breathing spontaneously with low SpO2?
are they on a ventilator or not
what should be done about a patient with low SpO2 who is on a ventilator?
check settings and connections and adjust accordingly
what often causes panting in the anaesthetised patient?
inadequate anaesthesia
what is paradoxical breathing often associated with in the anaesthetised patient?
respiratory obstruction
what is paradoxical ventilation?
where the abdomen rises and thorax falls on inspiration and then reverse on expiration
what may be causing an anaesthetised patient not to breathe at all?
post induction apnoea
depth of anaesthesia
drugs affecting respiratory drive
use of neuromuscular blocking agents
what effect can too light anaesthetic depth have on respiration?
breath holding
what effect can too deep anaesthetic depth have on respiration?
loss of respiratory drive due to depression of respiratory centres in the brain
how can drugs negatively affect respiratory drive?
decrease brain sensitivity to CO2 (main driver of ventilation) leading to hypercapnia
if a patient with low SpO2 is not breathing at all or has an abnormal pattern of ventilation what should you do?
squeeze reservoir bag
what are you looking for when you squeeze the reservoir bag when you are trying to discover why you patient has low SpO2?
does the chest rise as expected
can you hear gas leaks? - if so recheck ET tube
what should you do if you squeeze the reservoir bag and the thoracic cage doesn’t expand?
is there a mechanical issue like a sandbag/surgeon pressing on the chest - if yes, remove!!
what can you check for if the chest of your patient does not expand when the reservoir bag is squeezed but there is no external, mechanical issue?
is the chest open
could there be fluid or air in the thoracic cavity
could the ET tube or airway be blocked
why may the lungs not be able to contract after expansion?
there is a blockage in the expiratory gas pathway preventing this
what may be causing a blockage in the expiratory gas pathway preventing the contraction of lungs after expansion (on breathing)?
check t-piece bag is not twisted
is APL valve closed
check for kinks in breathing system tubing or heavy items compressing it
could ET tube or airway be blocked
what can cause respiratory tract obstruction?
kinked ET tube - tube too long
debris in ET tube or respiratory tract
foreign body somewhere in respiratory tract
what do you need to do if you have resolved issues with oxygen supply and are sure there are no obstructions to flow but the patient is still not breathing well?
ventilation needed - manual or IPPV
what is key about manual ventilation?
which care and only for a short period
why is a ventilator preferable to manual ventilation?
gives more control and better if will be required for longer
what should be included within patient monitoring as well as their physiological parameters?
checking equipment
what are other causes of hypoxaemia seen in compromised patients?
ventilation-perfusion mismatch
shunt or venous admixture
diffusion barrier
what ASA classification patients are at risk of hypoxaemia due to CVS/pulmonary compromise?
not usually 1 and 2 (3-5 more at risk)
what could be used if patients are judged to be at risk of hypoxaemia due to CVS/pulmonary compromise?
IPPV
what is the issue if all checks have been performed and patient still has low SpO2?
issue is with circulation/tissue perfusion
what are some of the causes of tachycardia during anaesthesia?
inadequate anaesthetic depth/inadequate analgesia hypercapnia hypoxia hypovolaemia/hypertension secondary to some drugs electrolyte abnormalities hyperthermia underlying conditions
what ASA category of anaesthesia is tachycardia due to inadequate anaesthetic depth often seen in?
1 and 2 undergoing routine procedures
what will tachycardia due to inadequate anaesthetic depth be associated with?
increased muscle tone
increased respiratory rate
increased BP
when may anaesthesia depth be adjusted?
in response to noxious and non-noxious stimuli - try and increase or decrease before these occur
what is a sign that your patients level of anaesthesia is too light?
movement
in what patients is tachycardia due to hypercapnia often seen?
ASA1 and 2 patients undergoing routine procedures
what will hypercapnia during anaesthesia most often be caused by?
inadequate respiration
how should tachycardia due to hypercapnia be treated?
as with steps for falling SpO2
what should happen to a dehydrated/hypovolaemic patient before anaesthesia?
should be stabilised unless it is an emergancy
what are the 2 effects of drugs that can lead to tachycardia?
direct or indirect
what are the direct causes of tachycardia due to drug action?
alfaxalone, ketamine, atropine and dopamine may all cause tachycardia in some patients
what are the indirect causes of tachycardia due to drug action?
anaphylaxis
what must be done before assuming that tachycardia is due to drug action?
rule out all other causes
when should electrolyte abnormalities and underlying conditions that may cause tachycardia during anaesthesia be picked up?
in pre-anaesthetic exam so should be aware prior to induction and patient should be stabilised
what are the main causes of bradycardia during anaesthesia?
patient too deeply anaesthetised drug effects increased vagal tone or vagal stimulation hypothermia severe hypoxia hypertension (reflex bradycardia) hyperkalaemia severe metabolic abnormalities (e.g. hypoglycaemia)
how can you check if bradycardia is due to anaesthetic depth?
check depth indicators (muscle tone, eye position, reflexes)
what is bradycardia due to deep anaesthesia seen alongside?
decreased respiratory rate and hypotension
what drugs can cause bradycardia in the anaesthetised patient?
opioids and alpha 2 agonists due to vagally mediated action (parasympathetic)
what can bradycardia due to drug action be treated by?
atropine (anti-cholinergic)
would bradycardia often be treated with anticholinergics?
no - unless worried about hypotension/reduced perfusion or arrhythmias
what patients may have high vagal tone leading them to be prone to bradycardia in anaesthesia?
brachycephallic dogs
what vagal reflex can be stimulated in some patients leading to bradycardia?
occulocardiac
what can be used to treat bradycardia due to high vagal tone/vagal reflex stimulation?
anticholinergic preemptively or when it occurs
how can bradycardia due to hypothermia be treated/avoided?
preserve body temperature during anaesthesia and monitor throughout
how can bradycardia due to hyperkalaemia be treated/avoided?
pre-anaesthetic checking/screening of potentially hyperkalaemic patients and stabilisation before anaesthesia
what patients have the potential to become hyperkalaemic?
those with renal failure, urethral obstruction and diabetics
how can bradycardia due to severe metabolic abnormalities be treated/avoided?
treat underlying cause/stabilise prior to anaesthesia
what is hypotension defined as?
mean arterial pressure below 60mmHg or systolic pressure measured using a doppler below 80mmHg
why should blood pressure be measured directly or indirectly rather than relying on pulses?
may still be able to feel weak pulse even with very low BP due to contraction of heart
what is hypotension due to?
one or more of the following:
reduced inflow to the heart
reduced pumping function of the heart
reduced vascular resistance
what are the main causes of hypotension during anaesthesia?
anaesthetic drugs
blood loss during surgery
pre-exisiting conditions
anaphylactic reaction to drugs, blood or blood products administered during anaesthesia
what pre-existing conditions can cause hypotension during anaesthesia?
hypovolaemia shock cardiomyopathy valvular heart disease arrhythmias hypothyroidism hypoxaemia Addisonian crisis
how should hypotension during anaesthesia be managed if likely due to anaesthesia?
turn down anaesthetic - may be all that is needed
if severe maybe turn off for 1-2 mins
IV crystalliod bolus
administer a positive inotrope like dopamine or epinephrine if it persists
ensure adequate ventilation and oxygenation
how should hypotension during anaesthesia be managed if cause is known?
treat primary problem (e.g. replace blood loss)
ensure adequate ventilation and oxygenation
what heart arrhythmia is shown on this trace?
ventricular fibrilation
what are the 5 main causes of accidents and emergencies during anaesthesia?
sick animal human error equipment failure inadequate preparation inadequate monitoring
how can accidents and emergencies during anaesthesia be prevented in sick animals?
stabilise before procedure if possible
postpone procedure
plan and have all equipment and drugs to hand
how can accidents and emergencies during anaesthesia be prevented due to human error?
check lists
communication during procedure
HALT - hungry, angry, lonely/late, tired - increases risk of human error
how can accidents and emergencies during anaesthesia be prevented due to equipment failure?
check all equipment before use
how can accidents and emergencies due to inadequate preparation during anaesthesia be prevented?
do not skimp time on preparation
how can accidents and emergencies during anaesthesia be prevented due to inadequate monitoring?
use eyes and ears at all times
what are common human errors during anaesthesia that lead to accidents and emergencies?
leaving APL valve closed drug administration errors airway management errors errors with positioning inadequate patient eye protection
what can drug administration errors be caused by?
incorrect calculation
incorrect route
wrong drug
perivascular administration
what are the key airway management errors?
failed intubation
traumatic intubation
both can lead to tracheal rupture
what are the main effects of positioning errors on patients?
EPAM - equine post anaesthetic myopathy pain compromised ventilation compromised cardiovascular function tourniquet effect (with resulting ischemia)
why can positioning errors cause so many problems for anaesthetised patients?
they are unable to move themselves if a position is painful and so damage can occur
what will result from inadequate protection of the eyes during anaesthesia?
corneal ulceration
why do eyes need protection during anaesthesia?
anaesthesia/sedation reduces tear formation
eyes are often open during anaesthesia with no blinking
how can eyes be protected during anaesthesia?
using bland ophthalmic ointment and avoiding eye trauma
what are the main mechanisms of respiratory failure?
depression of respiratory centre in brain
interruption of nervous/neuromuscular transmission
impaired movement of thoracic cage (e.g. sandbags or increased intra-abdominal pressure)
impaired lung movement e.g. pleural effusion
airway obstruction
what is cardiac arrest?
cessation of effective circulation
what are the main causes of cardiac arrest?
pre-existing cardiovascular disease anaesthetic overdose arrhythmias, cateholamine release hypovolaemia electrolyte/acid base abnormalities vagal reflexes hypoxia/hypercapnia/respiratory arrest
what often is a prewarning of cardiac arrest?
brady or tachycardia
what increases the chance of successful resuscitation?
early recognition of cardiac arrest
what may show on an ECG before cardiac arrest/during?
ventricular asystole
ventricular fibrillation
electromechanical dissociation/pulseless idioventricular rhythm
what blood pressure is classed as hypertensive?
> 120 mmHg MAP
what can cause hypertension?
nociception hypercapnia hypoxia drugs (inadequate anaesthesia or analgesia)
what causes vomiting / regurgitation during anaesthesia?
species and pain dependent
drug induced
length of pre-anaesthetic fasting (too short or too long)
when are the danger periods for vomiting / regurgitation?
induction and recovery
how can vomiting / regurgitation be prevented from leading to aspiration?
head elevated until ET tube placed and cuff inflated
what should be done if vomiting / regurgitation occurs?
head down
suction or swap out pharynx
consider IV omeprazole
record on anaesthetic record
what drug can be given to patients at risk of vomiting / regurgitation?
omeprazole
what are the risk factors for oesophageal reflux?
excessive / inadequate fasting
drugs
abdominal pressure increase
abdominal surgery / long ops
how can you tel that silent regurgitation has occurred?
may vomit blood tinged fluid in recovery
appear unable to swallow
appear distressed
what is helpful for avoiding anaesthetic accidents?
checklists
in what patient are anaesthetic emergencies more common?
sick patients
what body system does ECG give information about?
CVS
what are the key indications for use of ECG?
arrhythmia detected on auscultation
investigation of syncope
investigation of suspected cardiovascular disease
monitoring for arrhythmias in sick animals (e.g. ICU)
monitoring during anaesthesia
what is syncope?
fainting or passing out
which lead is anaesthesia ECG run from?
lead II
what information can be gained from ECG?
heart rate
ECG trace
what does ECG tell us about?
cardiac function - including heart rate, electrolyte imbalances, myocardial hypoxia, arrhythmias
what are the limitations of ECG?
no information on cardiac output / myocardial performance or blood pressure
pulseless electrical activity / electromechanical dissociation present after death
how can ECG electrodes be attached?
clips attached to adhesive pads placed on paws
crocodile clips with surgical spirit or ultrasound gel to improve contact
what method of ECG electrode attachment is preferable?
clips on pads as crocodile clips are painful in the conscious animal and can cause skin trauma
describe the ECG lead set up in small animals
red - right fore
yellow - left fore
green/black - left hind
describe the ECG lead set up in large animals
red - neck
yellow - sternum
green/black - over lateral thorax
on the small animal where is lead 1 located?
between red lead and yellow lead (left and right forelimbs)
on the small animal where is lead 2 located?
between red lead and green lead (right fore and left hind)
on the small animal where is lead 3 located?
between green lead and yellow lead (left hind and left fore)
what does the P wave on an ECG represent?
atrial depolarization
what does the QRS complex on an ECG represent?
ventricular depolarisation
what does the T wave on an ECG represent?
ventricular repolarisation
what is indicated by a tall P wave?
right atrial enlargement
what is indicated by a wide P wave?
left atrial enlargement
what is indicated by a tall R wave?
hypertrophy
what is indicated by a wide R wave?
left bundle bunch block
what is indicated by a deep S wave?
right ventricular hypertrophy
what is indicated by a wide S wave?
right bundle branch block
what is shown by the T wave?
myocardial ischemia or electrolyte disorders
what are the common ECG patterns seen with GA?
tachycardia bradycardia heart block premature ventricular contractions (VPC) fibrilation
what are the 2 types of cells within the heart?
working myocardial cells with the ability to contract
self excitatory cells with the ability to generate an impulse
what is automaticity?
cells that are able to generate an impulse
what cells within the heart are able to generate impulses?
sinoatrial node atrioventricular node perkinje fibres right and left bundle branches bundle of His
which cells of the heart produce the strongest and fastest electrical impulse and so coordinate the heart when it is working correctly?
SA node
what is the effect of other cells of the heart taking over impulse production?
there is a slower heart rate as they are less powerful
what is an arrhythmia?
a change in rhythm, rate or origin that differs from the normal cardiac cycle. Most are clinically insignificant and some are fatal
what happens during 1st degree block?
electrical signal doesn’t pass through the AV node as quickly as it should - a delay in conduction from atria to ventricles
how can 1st degree heart block be seen on a ECG trace?
prolonged distance between P and R waves - gap between P and QRS should be smaller than the gap from QRS to T
what is the arrhythmia shown on this trace?
1st degree block
what are the 2 types of second degree block?
Wenckebach
Mobitz
how many different types of second degree block are there?
2
how can Wenckebach second degree heart block be identified on a ECG trace?
progressive lengthening of P-R gap until QRS complex is missed totally
what is happening in the heart during Wenckebach second degree heart block?
impulse is prevented from travelling between atria and ventricles for increasing periods of time. At some point the gap will be so large that it will be missed altogether and the ventricles do not depolarise. The cycle will then begin again
how can Mobitz second degree heart block be identified on a ECG trace?
P-R is constant but intermittently QRS complexes are missed
what arrhythmia is occuring in this trace?
Mobitz second degree heart block
what is happening during Mobitz second degree heart block?
normal rhythm with occasional missed QRS complexes as impulse doesn’t reach AV node
what is happening in the heart during 3rd degree heart block?
complete AV block
different (but consistent) area of the heart is generating electrical impulses - ensures that blood still reaches tissues
how can you tell that a patient is suffering 3rd degree block from an ECG trace?
will be regular P waves and QRS complexes but not evenly spaced or in the ‘right’ order. May be some negative T waves
identify the arrhythmia in this trace
3rd degree block
how is ventricular tachycardia identified on an ECG?
wide ventricular complexes - do not look normal, fast HR
what is ventricular tachycardia caused by?
electrical impulse originating in the ventricles that is not led by the SA node
prior to what even may ventricular tachycardia be seen?
arrest
identify this arrhythmia
ventricular tachycardia
what can cause ventricular premature complex?
high sympathetic tone - pain, excitement, stress
electrolyte and acid base disturbances
some drugs
when are ventricular premature complexes clinically significant?
frequent, multifocal or in series as they may affect BP
how may ventricular premature complex be treated?
treat underlying cause
use drugs such as lidocaine
what is the name of this arrhythmia?
ventricular premature complex (VPC)
what is different about the equine ECG?
negative QRS complexes
why do equine ECGs have negative QRS complexes?
base apex lead configuration is used rather than the limb leads used in small animals - leads are in saggital plane rather than frontal
why will no enlargement of QRS complex or change in morphology be seen in equine ECG?
due to extensive perkinje network with the heart
what animal is this trace from?
horse
what are the main technical issues with ECG machines?
poor electrical contact
leads may fall off
electrical interference (e.g. diathermy, phones)
movement interference from animal
what should you do if you see a strange ECG trace?
check leads are on correctly
check placement of leads
try to screen shot or record a video of trace
where should any arrhythmias/different traces be noted on the GA sheet?
in the notes area with the right time assigned
what body system can be monitored using pulse ox?
CVS and perfusion
what 3 pieces of information can be gained from pulse ox monitoring?
haemoglobin oxygen saturation levels
heart / pulse rate
wave form (only some machines)
how can PaO2 be calculated?
multiply inspired fraction of oxygen by 5
what is the value of PaO2 normally around room temperature?
around 100
what is shown on an oxyhaemoglobin dissociation curve?
relationship between arterial oxygen concentration and % of haemoglobin saturated with O2
what are the advantages of handheld pulse ox?
can be taken anywhere
veristile
what are the disadvantages of handheld pulse ox?
susceptible to damage
needs charging
where does a pulse ox gain its background measurement of light absorption from?
muscle, tendons, ligaments and bones
how does pulse ox measurement work?
absorption of near-infrared light light by oxyhaemoglobin and red light by deoxyhaemoglobin means that levels of each can be emitted from LED on one side of probe and the amount absorbed on the other side used to calculate proportion of haemoglobin that has bound O2
how is pulse ox able to detect only arterial blood?
red light absorption will fluctuate in arteries along with cardiac cycle as blood volume does. Blood volume remains consistant in other tissues
how much red light is emitted by the pulse ox machine?
660Nm
how much infrared light is emitted by the pulse ox machine?
940Nm
what is the difference between oxyheamoglobin and deoxyhaemoglobin?
oxyhaemoglobin has all 4 subunits bound to O2, deoxyhaemoglobin is not carrying O2
what does Beers law state?
the amount of light absorbed increases or the light transmitted decreases as the concentration of the substance increases
what does lamberts law state?
intensity of transmitted light decreased exponentially as the distance traveled through a substance increases
what should be done when setting up pulse ox?
check unit for signs of damage
ensure batteries are in/charged or machine is plugged in
ensure probe is connected
test probe (use finger)
where can a pulse ox probe be placed?
anywhere hairless and non-pigmented tongue - ideal interdigital ear prepuce vulva skin webbing
what is the desired pulse ox measurement?
100%
at what saturation should you begin checking equipment, O2 supply and patient?
<95%
what SpO2 is concerning and requires immediate assessment?
<90%
what is a plethysmograph?
wave form of pulse ox on screen - mimics arterial BP trace and heart activity (will increase on systole and decrease on diastole)
what are the benefits of pulse ox?
non-invasive available in almost all settings non-painful quick and easy to set up and use gives a clear reading can be used on unconscious and conscious patients
what are the limitations of pulse ox?
false readings possible
susceptible to damage
doesn’t work in anaemic patients
can cause tissue compression in small animals
won’t work well on pigmented skin
patient movement can interfere
poor perfusion will affect reading
too thin tissue (e.g. cat ear) can cause poor reading
interference possible from overhead lights
no differentiation between carboxyhaemoglobin and oxyhaemoglobin so may see falsely elevated levels
why may SpO2 be read as high in anaeamic patients?
may read a well saturated RBC and so show high reading even though this is not the case for all RBC
how can issues with pulse ox machines be resolved?
re-position location of probe wet the area ensure it is working! change batteries/power source check for probe damage check patient! - MM, CRT etc
