Anaesthesia Flashcards
Define pain
Unpleasant sensory and emotional experience associated with or resembling that associated with actual or potential tissue damage
Define nociception
Neural process of encoding noxious stimuli
What is the difference between pain and nocicpetion
Pain is the interpretation of nociception, dependent on the individual, nociception can be present without pain
What is the purpose of pain and why does it need to be treated?
Protection
Can affect function and well-being of individuals
Define nociceptive pain
Pain from actual damage to non-neural tissues, activation of nociceptors
Define neuropathic pain
Pain from a lesion or disease to somatosensory system
Explain the difference between nociceptive and neuropathic pain
Nociceptive is in a normally functioning somatosensory system, neuropathic pain is in a damaged somatosensory system due to lesion or disease, harder type of pain to treat
Define hyperalgesia
Increased level of pain in response to a normally painful stimuli
Define allodynia
Pain from a normally non-painful stimuli
What is the differences between acute and chronic pain?
Acute- short term, acts as protection, can lead to chronic pain if untreated
Chronic- long term, generally not protective, causes suffering
What are physiological signs of pain?
Tachycardia Hypertension High body temperature Altered RR and pattern Release of stress hormones (adrenaline, cortisol etc.)
What factors affect how animals present signs of pain?
Species
Individual
Condition
Prey or predator
What are signs of pain common to dogs and cats?
Hunched over Pain face Lack of grooming Inappetence Condition specific signs
What are signs of pain in dogs?
Positive signs rather than reducing normal behaviour
Attention seeking
Submission
Vocalisation
What are signs of pain in cats?
Absence of normal behaviour Hiding Tense Fear-aggression Unwilling to have human contact
What are signs of pain in rabbits?
Tend to mask signs of disease Immobility Depression Closed eyes Not grooming Isolation Bruxism Hunched over Change in temperment
What are signs of pain in horses?
Fight or flight response Low head Vocalisation Grooming Agitation Restless Lameness Pain face Bruxism
Why is it important to be able to quantify pain?
Determine the course of treatment and assess if its effective and if the animal has a good quality of life
Name and briefly describe different methods of quantifying pain
Numerical rating scale- number pain 1-10
Visual analogue scale- marking pain on a line
Simple descriptive scale- provide description of pain to assign
What is the preferred method of assessing pain and how is it used?
Composite pain scale
Tailored to dogs and cats, has specific parameters that are assessed to determine pain
Analgesia provided for cats above 5/20 and dogs above 5/20 or 6/24
What are challenges of pain assessments?
Animal themselves can’t tell you what or where the pain is
Needs to rely on owner or vets judgement which is subjective
Some patients will have different reactions to pain, some hide it etc so hard to be definite
What are some methods used for chronic pain assessments and how do they work?
LOAD questionnaire- mobility questions scored 0-4
CSOM- 5 normal behaviours determined and assessed over time whether they engage with these and how they change with treatments
Videos- track changes in normal environment
Tend to look at patterns not one point in time
Why are chronic pain assessments important?
Aid decision on treatment, keeps it consistent or need for euthanasia
Define preventative analgesia
Administering effective analgesia before, during and after procedure
Why is preventative analgesia important?
Prevents upregulation of nervous system in noxious stimuli so lowers intensity and length of acute pain, should also reduce chronic pain
What is multi-modal analgesia?
Using different classes of analgesic agents and techniques
Why is multi-modal analgesia used?
No single analgesic will block all nociceptive pathways
Leads to more effective analgesia and lowers doses so reduces side effects
What are the legal requirements for opioids?
Controlled drugs so need CD cabinet, records of drugs
Full agonists- schedule 2, special prescription, storage, destruction and record keeping requirements
Partial agonists- schedule 3, special prescription requirements, buprenorphine needs to be locked in cabinet
How do opioids produce analgesia?
Act at endogenous opioid receptors in brain and spinal cord
Mu agonists are most effective at providing analgesia
Name examples of opioids of full and partial agonists and antagonists
Full agonists- methadone, fentanyl
Partial agonists- buprenorphine, butorphanol
Antagonist- naxolone
State the type of opioid, licencing, species used in, use and duration of action of fentanyl
Type of opioid- Full mu agonist
Licencing- cats and dogs
Species used in- cats, dogs, rabbits, horses
Use- intraoperative, short term infusions
Duration of action- minutes
State the type of opioid, licencing, species used in, use and duration of action of morphine
Type of opioid- full mu agonist Licencing- non Species used in- dogs, cats, horses Use- general acute pre-, peri- and post-op pain Duration of action- 2-4 hours
State the type of opioid, licencing, species used in, use and duration of action of methadone
Type of opioid- full mu agonist Licencing- cats and dogs Species used in- cats and dogs Use- general acute pre-, peri- and post-op pain Duration of action- 2-4 hours
State the type of opioid, licencing, species used in, use and duration of action of pethidine
Type of opioid- full mu agonist Licencing- dogs, cats, horses Species used in- mainly horses Use- general acute pre-, peri- and post-op pain Duration of action- minutes
State the type of opioid, licencing, species used in, use and duration of action of buprenorphine
Type of opioid- partial mu agonist Licencing- dogs, cats, horses Species used in- dogs, cats, rabbits Use- general acute pre-, peri- and post-op pain Duration of action- 6 hours
State the type of opioid, licencing, species used in, use and duration of action of butorphanol
Type of opioid- K agonist/mu receptor Licencing- dogs, cats, horses Species used in- dogs, cats, rabbits Use- general acute pre-, peri- and post-op pain Duration of action- 2 hours
How are opioids administered?
Usually IV, cant for pethidine
Well absorbed orally, SC, IM but oral has significant first pass metabolism
What are side effects seen when using opioids?
Respiratory depression- dose dependent, mainly when under anaesthesia
Sedation- more in dogs, dose dependent
Excitement- high doses, usually in pre-med
Bradycardia
Nausea- more in pre-med
Low GI motility- issue if using chronically
Urinary effects- when give epidurally
How do NSAIDs work to provide analgesia?
Inhibit prostaglandin production which are inflammatory mediators by inhibiting COX (cyclooxygenase) or LOX (lipoxygenase)
What are cautions that should be taken when using NSAIDs?
Metabolised by liver so care when patient has hepatic compromise
Care when patient is dehydrated or hypotensive
Can only use one in multi-modal analgesia
What NSAIDS and by what administration are licenced for dogs?
Meloxicam- injection, oral Carprofen- injection, oral Robenacoxib- injection, oral Ketaprofen- injection, oral Firocoxib- oral Phenylbutazone- oral Grapiprant- oral
What NSAIDS and by what administration are licenced for cats?
Meloxicam- injection, oral
Carprofen- injection
Robenacoxib- injection, oral
Ketaprofen- injection, oral
What NSAIDS are used in rabbits?
Meloxicam- most common
Carprofen- sometimes used
What NSAIDS and by what administration are licenced for horses?
Meloxicam- injection, oral Firocoxib- injection, oral Flunixin- injection, oral Phenylbutazone- injection, oral Ketaprofen- injection
What are common side effects of using NSAIDs?
GI ulceration- particularly if history, or has reduced drug clearance ability
Renal ischemia
Hepatopathy/liver disease- rare idiosyncratic reaction in dogs
CNS- unknown cause, dullness and lethargy in cats
When should dog and cat owners seek medical attention when using NSAIDs?
Vomiting, diarrhoea
General illness
When should horse owners seek medical attention when using NSAIDs?
Colic, diarrhoea, dehydration, weight loss
General illness
When should rabbit owners seek medical attention when using NSAIDs?
Anorexia, bruxism, depression, vomiting
Explain how local anaesthetics work as analgesics
Enter nerve fibres and block voltage-operated Na+ channels, stabilising membrane so blocks nerve conduction Blocks nociception (perception) before blocking proprioception (body position) and mechanoreception (stimuli detection)
What are the characteristics of local anaesthetics?
Weak bases
Only can cross lipid membranes and enter nerve cells when uncharged
When in higher pKa or lower pH more of drug is ionised so has slower and less effect
What are the two types of local anaesthetics and their properties?
Amide- i in name before caine, stable, broken down by cytochrome P450 liver enzymes, longer plasma half life
Ester- no i in name before caine, relatively unstable, rapidly broken down by cholinesterase so short plasma half life, PABA formed in hydrolysis which can be allergen
What are local anaesthetics used for?
Balanced anaesthesia
Desensitisation
Post-op pain relief
Lameness investigations
What is the licencing, species used in, length of action and other information about procaine?
Licencing- dogs, cats, horses
Species used in- dogs cats, horses, rabbits
Length of action- 50 minutes
Other- licenced versions contain adrenaline to vasoconstrict and keep in local area, least potent
What is the licencing, species used in, length of action and other information about lidocaine?
Licencing- dogs, cats, horses
Species used in- dogs, cats, horses, rabbits
Length of action- 20-40 minutes
Other- 2-5 minute onset, lower cardiotoxicity than bupivacaine, low potency
What is the licencing, species used in, length of action and other information about bupivacaine?
Licencing- none
Species used in- dogs, cats, rabbits
Length of action- 6 hours
Other- longer onset than lidocaine, most potent
What is the licencing, species used in, length of action and other information about mepivacaine?
Licencing- horses
Species used in- horses
Length of action- 2 hours
Other- used mainly for digit nerve blocks, more potent and toxic than lidocaine
What is the licencing, species used in, length of action and other information about ropivacaine?
Licencing- none
Species used in- small animals
Length of action- 6 hours
Other- lower CVS and CNS toxicity than bupivacaine, high potency
What is the licencing, species used in, length of action and other information about EMLA/eutectic mix of local anaesthetic/lidocaine and procaine?
Licencing- none
Species used in- rabbits
Length of action- 30-45 minutes
Other- topical, IV catheter placement
What is the licencing, species used in, length of action and other information about proparacaine and tetracaine?
Licencing- none
Species used in- cats, dogs
Length of action- 15 minutes in cats, 45 minutes in dogs
Other- opthalamogical preparations to desensitise cornea
Explain toxicity pharmacology for local anaesthetics
Increases as potency and dose increases
Causes neurotoxicity and CV toxicity
Prevented by not exceeding maximum dose, if need larger volumes dilute, aspirate to make sure isnt in vessels
How are local anaesthetics formulated?
Made into salt solution as otherwise poorly water soluble, does lower pH causing stinging on injection
What is meant by baricity?
Weight of one substance compared to another
How does baricity affect use of local anaesthetics in epidurals?
If moves into higher space could compromise respiratory muscles, need to add glucose to make solution heavier
What factors affect duration of action of local anaesthetics?
Lipid solubility
Strength of binding to channel
Speed of removal and metabolism
Why do vasoconstrictors get added to local anaesthetics?
Reduce speed of systemic absorption, prolongs duration of action, reduces toxicity and reduced bleeding at injection site
How does protein binding affect local anaesthetics?
Those that bind more readily have longer duration of action and lower toxicity risk as are only active when unbound
Side effects of local anaesthetics
Increased risk at increased doses
CNS- seen at lower doses, minor behavioural changes, muscle twitching, tremors, CNS depression, death
CV system- hypotension, dysrhythmias
Treat symptomatically as cant reverse local anaesthetics
What is paracetamol licenced for and when is it used?
Dogs, orally
Alternative to NSAIDs when contraindicated, useful to add to horse analgesia when in extreme pain. Toxic to cats
What is tramadol licenced for and when is it used?
Dogs, injection and oral
Also used in cats and rabbits, may cause GI motility decrease in horses
Alternative for opioids use at home, second analgesia in chronic pain
How does tramadol provide analgesia?
Acts centrally on mu opioid, noradrenergic and serotonergic systems
Wide therapeutic index but questions about efficacy
Should be used as co-analgesic
What analgesics have no licencing in animals and are used as second line anaesthesia to treat chronic pain?
Gabapentin
Pregabalin
Amantadine
Amitriptyline
How does gabapentin cause analgesia and what are side effects?
Binds to voltage gated calcium channels
Sedation, more when combined with tramadol, potentially toxic in liquid solutions with xylitol
What does pregabalin have a similar structure to and how does it differ?
Gabapentin
Better oral bioavailability and half life
What are features of amantadine?
NMDA receptor agonist
Antihyperalgesic, used along side other analgesics
Short duration of action
Renal excretion
How do you calculate fresh gas flow ml?
body weight (kg) x tidal volume (ml/kg) x respiratory rate x circuit factor
or
minute volume x circuit factor
How do you calculate drug volume (ml)?
(body weight (kg) x drug dose (mg/kg))/drug strength (mg/ml)
How do you convert mcg/kg to mg/kg?
mcg/kg / 1000
How to convert drug strength in % to mg/ml
% x 10
Define anaesthesia
Reversible state of production of state of unconsciousness
Define general anaesthesia
State of unconsciousness with absence of pain across whole body
Define local anaesthesia
Lack of sensation in localised part of the body
Define analgesia
Reduced pain
Define sedation
Alloying of excitement or irritability
Define premedication
Combination of drugs prior to inducing general anaesthesia
What is the purpose of anaesthesia?
Prevent pain and cause immobility to allow surgery and diagnostic testing
Define anxyolysis
Reduced anxiety
Define narcosis
Sleep like state
What is the risk of mortality due to anaesthesia in cats, dogs, horses and rabbits?
Cats- 0.24%
Dogs- 0.17%
Horses- 2.2%, 11.7% if colic
Rabbits- 1.39%
What increases risk of anaesthesia death?
If already sick
Extremes of patient size- unsuitable equipment
Aggressive patient- hard to examine pre-op, remove IV and ETT early
Drug sensitivities in certain breeds
Obesity- hard to inject IM, easily overdose as liver not bigger with higher body mass, more thoracic pressure so harder to breathe
Brachycephalic- harder to intubate, prone to gastroesophageal reflux, prone to dry eyes
What are the different classes of drugs in the schedule and examples?
1- no veterinary use, amphetamines 2- full mu agonists, morphine, fentanyl 3- barbiturates, tramadol, gabapentin 4- benzodiazepines, steroids 5- codeine, morphine in small doses
What is meant by anaesthetic triad?
Narcosis
Analgesia
Muscle relaxation
Define balanced anaesthesia
Anaesthesia produced by smaller doss of multiple drugs
Why is balanced anaesthesia used?
Anaesthetic triad cant be provided by a single agent
By using smaller doses of multiple drugs it lowers risk of side effects
What needs to be included in owner conversation and consent pre-op?
Explain procedure, risks, costs etc. Get full history Confirm fasting times Gain informed consent, sign documents Tell when they will hear from practice
Why is pre-op fasting recommended in dogs and cats?
Reduce risk of gastroesophageal reflux, regurgitation, aspiration
Help ventilation as less pressure on diaphragm
When should you not fast patients pre-operatively?
Not in rabbits as cause gut stasis
If too long excess stomach acid produced causing increased risk of reflux
What is checked in pre-op vet exam?
Full clinical exam, particularly MM for petechia, CRT, heart, pulses, respiration, temperature and any owner concerns
ASA classification
Drugs planned to use
Any diagnostic testing such as bloods or urine
What are the different ASA classifications?
I- normal healthy animal
II- mild systemic disease
III- controlled systemic disease
IV- severe uncompensated systemic disease
V- unlikely to survive 24 hours without intervention
Why are surgical checklists used?
Reduce rate of death and surgical complications
What preparation is taken before inducing an animal under anaesthesia?
Set up machines and equipment
Prepare medications, drugs and fluids
Place IV catheter
Premed patient
What is the purpose of premedication?
Calm patient
Lower risk of injury
Aid restraint
Decreases stress as stress hormones reduce response to anaesthesia
Pre-emptive pain relief
Reduce induction and maintenance drugs needed
Smooth induction and recovery
What are the routes of admin of premed?
IV
IM
SC
OTM
What are advantages and disadvantages of IV admin of premed?
Advantages- rapid onset, predictable effect
Disadvantages- need restraint and IV access
What are advantages and disadvantages of IM admin of premed?
Advantages- fairly rapid onset, predictable effect
Disadvantages- painful
What are advantages and disadvantages of SC admin of premed?
Advantages- easy administration
Disadvantages- not suitable for all drugs, slow onset, can be unpredictable
What are disadvantages of OTM admin of premed?
Not suitable for all drugs
Slow onset
Can be unpredictable
How does ASA grading affect premed protocols?
I and II- standard protocols and routine monitoring
III- stabilise prior, IV catheter and fluids in place
IV and V- same as III, also brief owners on risk, calculate and draw up first CPCR medication doses
What premedication protocols are typically used for cats and dogs with ASA I or II?
ACP + opioid
Alpha 2 agonist + opioid
What premedication protocols are typically used for dogs with ASA III?
ACP + opioid
Benzodiazepine + opioid
What premedication protocols are typically used for cats, dogs and rabbits with ASA VI or V?
Benzodiazepine + opioid
Benzodiazepine + ketamine
Opioid alone
What premedication protocols are typically used for cats with ASA III?
Benzodiazepine (midazolam) + ketamine
What premedication protocols are typically used for rabbits with ASA I or II?
ACP + opioid
Alpha 2 agonist + opioid
Fluanisone alone or with benzodiazepine
What premedication protocols are typically used for rabbits with ASA III?
Benzodiazepine + opioid
Name the classes of drugs used for premedication
Phenothiazines Alpha 2 agonists Benzodiazepines Butyrophenones Opioids
How do phenothiazines act in the body and what effects do they produce?
Dopamine receptor antagonist in CNS
Sedation
How do alpha 2 agonists act in the body and what effects do they produce?
Alpha 2 adrenergic receptor in CNS
Sedation, analgesia, muscle relaxation
How do benzodiazepines act in the body and what effects do they produce?
Enhance GABA at GABA alpha receptor
Sedation, minor tranquiliser, muscle relaxation, anticonvulsant
How do butyrophenones act in the body and what effects do they produce?
Dopamine receptor antagonist in CNS, interferes with GABA, norepinephrine, serotonin mediated activity
Sedation
How do opioids act in the body and what effects do they produce?
Endogenous opioid receptors in CNS
Sedation, analgesia
Which drug is a phenothiazine, what is its licencing and what is it used for?`
Acepromazine
Cats and dogs for pre-med and sedation often in combination with opioids
How is acepromazine administered and how does each method effect time to peak effect?
SC
IM- 30-40 minutes
IV- 10-15 minutes
How long is duration of action of acepromazine and how is it eliminated?
4-6 hours
Liver metabolises
Why can’t acepromazine be given orally?
Poor oral bioavailability
What are side effects of acepromazine?
Peripheral vasodilatation causing lowered body temperature, and blood pressure
What are examples of alpha 2 agonists and what are they licenced for?
Dexmedetomidine Medetomidine Romifidine Xylazine Cats, dogs and rabbits
How is dose of alpha 2 agonists calculated and why is it done this way?
Very potent so done by body surface area
How are alpha 2 agonists administered and how does this effect time to effect?
IV- rapid effect after 5 minutes
IM- effect after 15 minutes
What agent can be used to reverse alpha 2 agonists?
Atipamezole
If not reversed what is the duration of action of alpha 2 agonists and how are they metabolised?
2-3 hours
Liver metabolism
What are side effects of alpha 2 agonists?
Bradycardia Reduced CO Second degree AV block Hypertension initially then hypotension Respiratory depression GI stasis Hyperglycaemia Increased urine production Uterine contractions
What are examples of benzodiazepines and what are they licenced for?
Diazepam in cats and dogs
Midazolam in horses
How are benzodiazepines administered?
IV by slow infusion as rapidly crosses blood brain barrier
How are benzodiazepines metabolised?
Liver
How does duration of effects of diazepam and midazolam differ?
Diazepam has shorter half life but longer length of action as its metabolites are active
What is the reversal for benzodiazepines and why is it rarely used?
Flumazenil
Very expensive
What are side effects of benzodiazepines?
Mild dose dependent respiratory depression
Minimal CVS effects
What is an example of butyrophenones and what is it licenced for?
Fluanisone, only in combination with fentanyl
Small furries
How is sedation as a result of benzodiazepines improved?
Combining with opioid, ketamine or alpha 2 agonist
What is the duration of action of fluanisone?
30-60 minutes
What is the result of combining benzodiazepine with fluanisone?
20-40 minutes of muscle relaxation
What are side effects of fluanisone?
Respiratory depression
How are opioids metabolised?
Liver
How should you care for premedicated or sedated patients?
Keep in quiet environment
Regular but preferably continuous monitoring of ABC, TPR, CRT, MM
What are common issues when patients have been premedicated?
Excitement Excess sedation Airway obstruction CVS up to and including cardiac arrest Decompensation of existing conditions
Why is sedation used?
Allow procedures that would be impossible in fully conscious animals
Handling anxious, dangerous or feral animals
Keeping still for radiography
Minor procedures such as wound dressing
What drugs and protocols and used for sedation?
Same as premedication but higher doses
State the main method of admin of premed
IM
What is mean by induction phase?
Taking patient from conscious to unconscious state
Why should you pre-oxygenate patients before induction?
Give more time to place ETT before decompensation
What are the different methods of admin of injectable induction?
IV- titrate to effect, 2-10 minute onset, reliable, little stress to animal, does need IV access
IM- 10-20 minute onset, reliable, painful
SC- easy, less painful, 30-45 minute onset, lower efficacy, less reliable
What are different methods of inhalational induction?
Face mask- held tightly over face, cheap, easy, can give oxygen and VA quickly, lacks air way protection, not always tolerated, increased deadspace, harder to monitor, cant IPPV
Chamber- good when cant get IV, easy, cheap, stressful for animal, hard to observe
Why is injectable induction prefered?
Prevents risk of exposure to staff of inhalant VA
What needs to be considered when restraining for induction?
Minimal as possible physical restraint but ready for more
Dont compromise ventilation
Chemical restraint as needed
What are risks involved to the patient with restraining for induction?
Stress
Respiratory compromise
Cardiac arrhythmia
Raised ICP and IOP
Why do you need to restrain for induction?
Aid tube and catheter placement
Keep patient and staff safe
How does a laryngeal mask airway work and why are they uncommonly used?
Sits over larynx
Not designed for veterinary species
How do v-gels work and what are advantages and disadvantages?
Sits in pharynx forming secure seal over trachea
Advantages- can be reused, structure mirrors anatomical structure, useful in rabbits
Disadvantages- species and weight specific so need range, need to be trained to use
What is the gold standard for airway management and why?
Endotracheal tube
Prevent atmospheric exposure, protects airway and allows accurate provision of gases
What is the benefits of a cuffed ETT?
Prevents gas leakage and aspiration
What are the different types of cuffs on ETT?
Low volume high pressure- pressure produced on small area of trachea
High volume low pressure- pressure evenly distributed on larger area
What are safety features present on ETT?
Murpheys eye- hole in side of tube to allow ventilation if end of tube is blocked
Armoured- only some tubes, inner wire to prevent kink if in awkward position
List equipment needed for intubation
Laryngoscope ETT- length reaches from incisors to shoulder tip Local anaesthetic- cats to prevent laryngeal spasm Tie Cuff syringe Swab Suction Mask to pre-oxygenate
How do you check ETT is in correct place?
Leak test Capnograph trace (gold standard) Visualise tube between vocal folds Condensation in clear tubes Feel air movement
What are common complications during induction?
Injury to patient and staff Lack of airway patency Aspiration and regurgitation Hypothermia CV and respiratory effects from anaesthetic agents Post induction apnoea
What are common complications involving the ETT during maintanance?
Twisted
Disconnected
Extubation
Wrong tube size placed
What factors determine technique used for anaesthetic maintenance?
Species Behaviour Access to IV Procedure Facilities Expertise
What is the purpose of anaesthetic machines?
Delivery of oxygen and volatile gases to the patient
How should oxygen cylinders be stored?
Under cover, clean and dry
Indoors in well ventilated fireproof room
Not exposed to extreme heat, cold, flammable or combustible materials
Empty and full seperate
F, G, J stored vertically
C, D, E stored horizontally
How should you handle oxygen cylinders?
Hold correctly or move with trolley
What are the pressures inside oxygen and nitrous oxide cylinders?
Oxygen- 13700kPa
Nitrous- 4400kPa
How much do E, F and J oxygen cylinders hold?
E- 680 litres
F- 1360 litres
J- 6800 litres
What is a cylinder yolk on anaesthetic machine and what is its function and key features?
Area that holds cylinders in place, specific to each type of gas
Provides tight bodok seal to keep unidirectional flow
Has pin index safety system to make sure correct cylinder attaches
What do the different coloured pipelines supply?
White- oxygen
Nitrous- blue
Black- medical air
How are pipelines prevented from misconnection?
Connect to anaesthetic machine Schrader socket with their Schrader probe (unique diameter index collar to correspond to socket)
What are NISTs on pipeline and what is their purpose?
Non-interchangeable screw thread
Unique for each gas and has valve for one way flow
What is the function of pressure gauges on anaesthetic machines?
Indicate gas cylinder and pipelines pressure so shows when cylinder needs changing
What is the purpose of pressure regulators on anaesthetic machines?
Reduces pressure of gas from the cylinder to prevent damage
Compensate pressure as it decreases when cylinder empties
Smooth pressure fluctuations
How does an oxygen failure alarm work?
Alarm when oxygen supply falls below 200kPa
Should also cut off nitrous delivery
What is the purpose of hypoxic guard?
Prevent hypoxic mixture being delivered as nitrous is cut off when oxygen falls below 130-70kPa
Linked valves means minimum 1:1 ratio is maintained
Oxygen always on if nitrous is
How does a non-return pressure relief safety valve work?
One way valve preventing backflow to gas machine, opens when back bar pressure is more than 35kPa
What is a flow meter?
Measures flow of each gas passing through
What are the components of a flow meter?
Flow control valve- fine adjustment of gas flow, reduces pressure from 420kPa to 100 kPa
Tapered transparent tube- visual scale of gas flow
Bobbin or ball- rotates in tube as gas passes around
How do you read the bobbin and ball in flowmeter?
Bobbin- top
Ball- centre
What is the function of a vaporiser?
Contains volatile liquid anaesthetic agent picked up by gas from flow meter to deliver to patient
How do calibrated vaporisers work?
Gas entering from flowmeter goes down bypass channel or into chamber above liquid anaesthetic to pick up anaesthetic
Control valve adjusts how much gas goes to vapour chamber determining concentration of anaesthetic agent picked up
What is the effect of temperature cooling on vaporisers and how is it minimised?
Bi-metallic strip bends to resistance is reduced and more gas passes through VA chamber so more anaesthetic is delivered to the patient
Housed in brass and has TEC/temperature compensating mechanism
What is the purpose of wicks and baffles in vaporisers?
Wicks- increases surface area for anaesthetic agent to evaporate
Baffles- direct incoming gas to surface of liquid
What is the function of the back bar on anaesthetic machines?
Connects vaporiser by selectatec and interlock systems
