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
What is the common gas outlet on anaesthetic machines?
Attaches breathing systems to deliver gases to patient
What is the purpose of oxygen flush and how does it work?
Remove gas from system in an emergency
Supplies oxygen at 400kPa and 35-75l/minute, bypassing flowmeter and vaporiser
When should you never use the oxygen flush?
When connected to the patient
What is meant by scavenging?
Removal of environmental contaminants as waste VA and gases are subject to COSHH and HASAWA
Describe active scavenging
Waste anaesthetic agents drawn outside of building by fan and vent system, with air break to prevent negative pressure on patients breathing effort
Describe passive scavenging
Gas pushed by patients expiratory effort to outside building with increases resistance or into activated charcoal canister
How do oxygen concentrators work?
Take in and purifies air using molecular sieve to remove nitrogen from air
How is liquid oxygen stored?
In cold specific container, liquifies at -183 degrees, with vacuum installed evaporator
Outside
How is liquid oxygen used?
Oxygen drawn off as needed, passed through vaporiser and turned to gas to enter pipes, flow regulated by control pannel
Name safety features present on anaesthetic machines
Pin index system NIST on pipelines Colour coding Touch coded oxygen flowmeter (easier to turn than others) Ratio regulators Nitrous cut off and alarms Air intake valve Reserve oxygen cylinders
How are staff kept safe when using anaesthetic machines?
Well ventilated rooms, 15-20 air changes per hour
IV induction when possible
Cuffed ETT
Connect breathing system before turning on VA
Low flow techniques
Leak check
Oxygen flush before disconnecting
Fill vaporiser with key and at end of day
Monitor exposure
Define dead space
Volume of gas that doesn’t eliminate carbon dioxide
Define tidal volume
Volume of gas entering lungs on each inspiration
Define minute volume
Volume of gas entering lungs per minute
Define metabolic oxygen requirements
Oxygen required each minute for metabolic processes
Define rebreathing
Inspired gases reaching alveoli contain more carbon dioxide than can be accounted by just inhalation from patients dead space
List functions of anaesthetic breathing systems
Provides oxygen and anaesthetic agents via common gas outlet to airway management device
Allow IPPV or spontaneous ventilation
Allow scavenging of expired gases
List components of breathing systems
Reservoir bag
APL/adjustable pressure limiting valve
Tubing
Soda lime in circles
What is the rough estimate for the size of reservoir bag to use?
3-6x tidal volume
What is the effect of leaving the APL valve closed?
Reservoir bag extends System becomes high pressure Thoracic movement reduces Tachycardia, hypoxia Pneumothorax, pneumomediastinum Death
How is resistance of tubing effected?
2x length = 2x resistance
2x radius = 16x less resistance
What are the two arrangements of tubing in breathing systems?
Parallel- tubing lies next to each other
Coaxial- one tube inside the other
What is the purpose of soda lime in circles?
Absorbs carbon dioxide in exothermic reaction
What factors affect the choice of breathing system used?
Size of patient Valve position IPPV requirement Ease of scavenging Cleaning and sterilisation Heat and moisture retention
What is the impact of increased resistance in breathing systems?
Low RR, altered pattern and increased effort
Decreased tidal volume
Hypoventilation, hypoxia, hypercapnia
Light plane anaesthesia due to reduced alveolar ventilation
What causes increased dead space in breathing systems?
Long ETT
Part of system used
What is the effect of increased dead space?
Increased PaCO2
Increased work of breathing to increase minute volume
What are the two types of breathing systems?
Non-rebreathing
Rebreathing
How do non-rebreathing systems work?
Fresh gas flow removes expired carbon dioxide
What are advantages and disadvantages of non-rebreathing systems?
Advantages- inspired agent same as shown on vaporiser, low resistance, light weight, cheap
Disadvantages- more expensive, heat and moisture lost, increased risk of pollution
State patient weight requirement, circuit factor, resistance, dead space and drag, ability to scavenge and location of bag for T-piece
Weight- less than 10kg
Circuit factor- 2-3
Resistance, dead space and drag- low resistance and dead space, reasonable drag
Ability to scavenge- hard unless APL valve present
Location of bag- expiratory limb
State patient weight requirement, circuit factor, resistance, dead space and drag, ability to scavenge and location of bag for bain
Weight- over 8-10kg and under 15-20kg Circuit factor- 2-3 Resistance, dead space and drag- low drag and dead space Ability to scavenge- easy Location of bag- expiratory limb
State patient weight requirement, circuit factor, resistance, dead space and drag, ability to scavenge and location of bag for lack
Weight- over 10kg less than 25-30kg, mini for over 1kg
Circuit factor- 1
Resistance, dead space and drag- moderate
Ability to scavenge- good
Location of bag- inspiratory limb
Which breathing systems can be used for IPPV?
T-piece
Bain
Circle
How do rebreathing systems work?
Soda lime removes expired carbon dioxide
What are advantages and disadvantages of circle?
Advantages- lower FGF so lower pollution, less expensive to run, heat and moisture retained
Disadvantages- Slow changes in inspired anaesthetic agent concentration, higher resistance
How is FGF calculated in circles?
Metabolic oxygen requirement
5ml/kg for large animals, 10ml/kg for small animals
What is the weight requirement and resistance of circles?
Weight- over 10-15kg
Resistance- high due to unidirectional valves and soda lime canister
What are the features of an ideal injectable anaesthetic agent?
Rapid onset Non-irritant allowing IM or IV admin Minimal cardiopulmonary effects Rapid metabolism and elimination Non-cumulative to allow top ups Good analgesia and muscle relaxation
What are injectable anaesthetic agents commonly used for?
Induction of anaesthesia
Along side inhalational anaesthesia for balanced technique
Triple for short term anaesthesia- alpha 2 agonist, opioid, ketamine IM
TIVA
Euthanasia
What factors affect the effect of injectable anaesthetics?
Blood flow to brain- need to cross BBB Amount of non-ionised drugs- brain protected from ionised drugs Lipid solubility- BBB is lipid Molecular size Concentration gradient Protein binding- only unbound cross BBB Distribution and metabolism Excretion
Why is TIVA used?
Reduce exposure to inhalational anaesthetics
Allow anaesthesia without access to machines
Maintain stable plane of anaesthesia as no bolus
What are the disadvantages of TIVA?
Can have longer recovery
Complicated calculations need to be done for dosing
What are ideal properties of injectable anaesthetic agents that make it suitable for TIVA?
Rapid metabolism and elimination
Fast onset
High therapeutic index
Pharmacokinetics available to allow CRI dose calculations
List the injectable anaesthetic agents available for use in animals
Propofol Alfaxalone Ketamine (mainly used^) Tiletamine Zolazepam Thiopental
What is licencing for propofol and how is it typically administered?
Cats and dogs
IV as irritant otherwise
What is the drug class and mode of action of propofol?
Drug class- substituted phenol
Mode of action- GABA agonist (enhances inhibitory GABA in CNS)
State the speed of onset and length of effect for propofol
Rapid onset
5-10 minutes effect
What are features of propofol (protien binding, solubility, metabolism and elimination, cumulation)?
Highly protein bound
Lipid soluble
Rapid liver metabolism and elimination
Cumulative in cats (lack glucorinidation pathway) not in dogs
What physiological effects can be seen after propofol admin?
Post induction apnoea
Hypotension from myocardial depression and peripheral vasodilation
What components of the anaesthetic triad are provided by propofol?
Muscle relaxation
No analgesia
What is the difference between propofol with and without preservatives?
Non-preservative containing- discard whats not used in dose, used for TIVA Preservative containing (benzyl alcohol)- can store 28 days once opened
What is licencing and administration method of alfaxalone?
Cats, dogs and rabbits
IV, maybe irritant if IM
What is alfaxalones drug class and mode of action in the body?
Neuroactive steroid GABA agonist (enhances inhibitory GABA in CNS)
What is the formulation of alfaxolone?
Clear solution containing cyclodextrin ring as alfaxalone isnt water soluble without
State features of alfaxalone (protein binding, speed of onset, metabolism, length of effect, cumulation)
20-50% protein bound Rapid onset Rapid liver metabolism and elimination 15-30 minute effect Non-cumulative
What are potential physiological effects seen after alfaxalone admin?
Respiratory depression
Post induction apnoea
Tachycardia as response to hypotension
What is licencing and method of admin for ketamine as injectable anaesthetic?
Cats, dogs and horses
IV and IM
What is ketamines drug class and mode of action?
Drug class- phencyclidine derivative
Mode of action- NMDA antagonist (dissociative anaesthetic)
Why is ketamine not used as a sole anaesthetic agent?
Muscle relaxation is poor and reflexes are maintained
State features of ketamine when used as anaesthetic agent (speed of onset, length of effect, cumulation and metabolism, excretion, protein binding)
Slow onset so need calm environment 20-40 minute effect Non-cumulative through active metabolite by liver nor-ketamine Renal excretion 50% protein bound
What can be physiological effects seen after administering ketamine?
Increased IOP and ICP
What components of the anaesthetic triad does ketamine provide?
Analgesia (and antihyperalgesia)
When is ketamine most commonly used as an anaesthetic agent?
Horses for maintenance by TIVA
Cats IM as sedative or IV for induction
What is tiletamine licencing and how is it administered?
Dogs and cats
IV or IM
What is the mode of action of tiletamine?
NMDA antagonist
What is licencing and mode of action of zolazepam?
Dogs and cats
GABA agonist
What are the features of thiopental (mode of action, formulation, pH, speed of onset, protein binding, metabolism, cumulation)?
Barbituate acting at GABA receptor Powder, 2.5% or 5% Alkaline Rapid onset Highly protein bound Metabolised after redistributing Does accumulate
What can be physiological effects seen after admin of thipental?
Perivascular tissue necrosis
Cardiorespiratory depression
Short term ventricular bigeminy (alternating normal sinus and premature ventricular complexes)
Define volatile anaesthetic
Liquid at room temperature changes to vapour and inhaled to produce general anaesthesia
What are the main uses of inhalational anaesthesia?
Maintenance of anaesthesia
Induction
What are the advantages and disadvantages of inhalational anaesthesia?
Advantages- easy to administer and calculate doses, can be used for most patients
Disadvantages- higher risk of death, exposure to staff
List ideal properties of inhalational anaesthetic agents
Non-irritant to MM Minimal cardiopulmonary effects Rapid uptake and elimination Non-toxic Non-flammable and chemically stable Easily vaporised Provide good analgesia and muscle relaxation
Define MAC and state what it stands for
Concentration required to prevent purposeful movement in response to supramaximal noxious stimuli in 50% of patients
Minimum alveolar concentration
Define MAC sparing
Reducing MAC by use of other drugs
What increases and decreases MAC?
Increases- hyperthermia, young animals, hyperthyroidism
Decreases- drugs, hypothermia, pregnancy
How does MAC affect potency?
Higher MAC the less potent a drug
What factors affect uptake of inhalational anaesthetic agents?
Concentration in inspired air- higher has quicker uptake
Alveolar ventilation- higher increases uptake
Blood gas solubility- lower increases onset and recovery as moves to target organ faster
CO- lower increases onset and recovery as rapidly increases alveolar concentration so picked up in blood
Blood tissue solubility- affects distribution
How are inhalational anaesthetics eliminated?
Metabolism
Biotransformation
Exhalation
What needs to happen for animals to recovery from anaesthetic in terms of levels of agent?
Needs to be low enough in CNS
What are side effects to animals when using inhalational anaesthetics?
Cerebral
CV
Respiratory
What are effects to humans when exposed to inhalational anaesthesia?
Mutagenic
Tetragenic- cause congenital disorders
Reduced fertility
Renal and hepatic disease
How are inhalational anaesthetics used safely?
Avoid staff exposure Avoid gaseous induction Inflate cuff before turning on vaporiser Keep patient on breathing system for few minutes to allow VA scavenging Recover in well ventilated area Training to deal with spillages
Which inhalational anaesthetic agents are licenced for cats and dogs?
Isoflurane
Sevoflurane
State features of isoflurane (whether irritant, toxicity, stability, ease of vaporising, MAC)
Irritant to airways and MM Toxic Stable and non-flammable Easily vaporised MAC- 1.4-1.6
State features of sevoflurane (whether irritant, toxicity, stability, ease of vaporising, MAC)
Non-irritant to airways and MM Toxic Stable in presence of soda lime, flammable in oxygen or nitrous Easily vaporised MAC- 2.1-2.6
What elements of the anaesthetic triad are achieved by isoflurane?
Muscle relaxation
No analgesia
What elements of the anaesthetic triad are achieved by sevoflurane?
No analgesia or muscle relaxation
State physiological effects associated with isoflurane use
Vasodilation Hypotension Respiratory depression, hypoventilation, hypercapnia Bronchodilation Reduced renal and hepatic perfusion
State physiological effects associated with sevoflurane use
Cerebral vasodilation, increase intercranial blood volume
Hypotension
Respiratory depression, hypoventilation, hypercapnia, less than isoflurane
Bronchodilation
Reduced renal and hepatic perfusion
How does uptake and elimination differ between isoflurane and sevoflurane?
Iso- slower, blood gas solubility 1.4, 1% metabolic elimination
Sevo- faster, blood gas solubility 0.69, 3% metabolic elimination
Which inhalational anaesthetics no longer have licencing?
Halothane
Desflurane
What is nitrous used for in anaesthesia?
Analgesic
What is meant by nitrous second gas effect?
Inhaled gas higher in alveoli than blood so nitrous diffuses into blood and isoflurane in alveoli is in much higher concentration
What is meant by diffusion hypoxia of nitrous?
Equal nitrous and oxygen delivered and in blood, nitrous stopping causes it to rapidly diffuse to alveoli diluting alveolar oxygen
State features of nitrous as anaesthetic gas (uptake and elimination, MAC, ratio given with oxygen)
Rapid uptake and elimination due to being insoluble
MAC over 100%
1:2 with oxygen in non-rebreathing systems
1:1 with oxygen in rebreathing systems
Why should 100% oxygen be provided for 5-10 minutes after turning off nitrous?
Compensate hypoxia
Why is it important to position patients correctly under anaesthesia?
Support joints to prevent muscle or nerve damage
Prevent pain post-op
Optimise ventilation
Aware of nasal congestion
Why do you need to use GA records and how often are they updated?
Legal requirement
Every 5 minutes, sometimes continuous if needed
What should be recorded on anaesthetic records?
HR RR Temperature BP Pulse oximetry Drug doses, oxygen, anaesthetic gas Start time, date, finish time, critical event
What parameters are monitored under anaesthesia?
Depth of anaesthesia CV system Respiratory system Drug administration Temperature Urine output Blood parameters Neuromuscular function Pulses Eye position MM CRT
In what ways can heat be lost when anaesthetised?
Convection- loss of heat to cool air
Conduction- loss of heat to surfaces in contact
Radiation- loss of heat to structures not in contact
Evaporation- loss of heat from moisture evaporation
What factors of patients will increase heat loss?
High surface area: body weight Low fat Thin hair Exposed internal tissues Extreme age
Why does anaesthesia cause hypothermia?
Increase blood flow from core to periphery so more heat lost
Reduced metabolic rate reducing heat produced
What are the effects of hypothermia?
CNS depression Hypotension Bradycardia Hypoventilation Low metabolic rate Low urine output
How do you minimise the risk of hypothermia?
Minimal anaesthetic time Minimal wetting of patient when scrubbing High ambient temperature Appropriate breathing system Warmed fluids Use insulating materials or heat sources
What information does a capnograph give you?
Inspired carbon dioxide
Expired carbon dioxide
RR
Capnograph trace
What are the normal ranges for end tidal carbon dioxide in cats and dogs?
Cats- 28-35
Dogs- 35-45
What causes high and low end tidal carbon dioxide?
High- hypoventilation due to reduced RR and tidal volume
Low- hyperventilation, low CO, low metabolic rate, hypothermia, pulmonary embolism, leak in sample line or breathing system
What causes high inspiratory carbon dioxide in non-rebreathing and rebreathing systems?
Non-rebreathing- too low FGF or too much dead space
Rebreathing- exhausted soda lime, faulty valves
What are the two types of capnography machines and how do they work?
Side stream- takes small sample of air through sample line to machine for analysis
Mainstream- gas analysed in breathing system using infrared detectors of absorption by carbon dioxide
State advantages and disadvantages of side stream capnography
Advantages- cheaper, less likely to break, easy to replace
Disadvantages- delay in readings, when low FGF can take large proportion, easily damaged sample line
State advantages and disadvantages of mainstream capnography
Advantages- real time, doesnt effect FGF
Disadvantages- expensive, easily damaged, adds drag
What are some advantages of capnogrpahy?
Non-invasive
Easy to set up and use
Effective monitoring of ventilation
Informs about CO (low carbon dioxide implies low CO)
What are some disadvantages of capnography?
Increased dead space
Need ETT
Takes time to learn normal or abnormal
What information is shown on ECG and how is this used?
ECG trace and HR
Non-diagnostic, look for normal and report abnormal
What is meant by electromechanical dissociation?
Pulseless electrical activity of the heart few minutes post death
What are common abnormalities that can be interpreted from ECG trace?
Electrolyte imbalance
Myocardial hypoxia
Arrhythmias
What are indications for use of ECG?
Arrhythmias on auscultation Investigating syncope/fainting Investigating CV disease Monitoring arrhythmia General monitoring
How is ECG attached to paitents?
Clips or adhesive pads in good contact with skin, improved with ultrasound gel or surgical spirit
What ECG leads are used in small animals?
Red- right fore
Yellow- left fore
Green- left hind
What ECG leads are used in large animals?
Red- neck
Yellow- sternum
Green- lateral thorax
What are potential reasons for abnormal ECG traces?
Poor contact
Leads fallen off
Electrical or movement interference
What do the different waves on the ECG represent?
P- atrial depolarisation
QRS- ventricular depolarisation
T- ventricular repolarisation
What is different about equine ECG compared to normal ECG?
Upside down QRS complex as leads are base apex not limbs
What do some ECG abnormalities mean (tall p wave, wide p wave, tall r wave, wide r wave, deep s wave, wide s wave, abnormal t wave)?
Tall p wave- right atrial enlargement
Wide p wave- left atrial enlargement
Tall r wave- hypertrophy
Wide r wave- left bundle branch block
Deep s wave- right ventricular hypertrophy
Wide s wave- right bundle branch block
Abnormal t wave- myocardial ischemia, electrolyte imbalance
What is commonly seen on ECG traces under anaesthesia?
Tachycardia Bradycardia Heart block Premature ventricular contraction Arrhythmia/fibrillation
What is a 1st degree block and how is it shown on ECG?
Signal held up in first part of cycle
Long PR distance
What are the two types of 2nd degree block?
Wenckebach- lenghtening of PR until beats lost and impulse blocked
Mobitz- sudden beat loss
What are 3rd degree blocks?
Complete block to signal at AV node, fatal
What are the causes of ventricular premature comples?
High sympathetic tone
Electrolyte acid base imbalance
What information does pulse oximetry give?
Haemoglobin oxygen saturation
HR
Pulse rate
How does pulse oximetry work?
Probes emit and detect light which changes dependent on oxyhaemoglobin (absorbs more infrared) and deoxyhaemoglobin (absorbs more red light)
Only works on arterial blood
Where should pulse oximeter be placed?
Hairless and non-pigmented area Tongue Interdigital Ear Prepuce Vulva Skin webbing
What do different haemoglobin saturations mean?
100%- best case
95-100%- good
90-95%- start to worry
Less than 90%- very concerned
Define plethysmography
Trace mimicking arterial blood pressure on pulse oximeter
What is a diachronic notch seen on plethysmograph caused by?
Aortic valve closing and distending aorta contracts causing brief arterial pressure change
What are advantages of pulse oximetry?
Non-invasive
Widely available
Easy to set up and use
Can be used when conscious or unconscious
What are disadvantages of pulse oximetry?
Can give false readings
Easily damaged
Not good if anaemic as shows good saturation even if have very low numbers of RBC
Large probes can compress small animal tissues
Ineffective if poorly perfused
False elevation with carboxyhaemoglobin
What should you do if there are problems with pulse oximeter?
Reposition probe
Wet area
Test on own finger
Check actual patient status
Define blood pressure
Measurement of pressure exerted by blood on walls of blood vessels
Why does anaesthesia effect BP?
Drugs are vasodilatory
What are advantages and disadvantages of direct BP measurements?
Advantages- accurate, reliable, beat to beat information
Disadvantages- invasive, need experience, risk of infection and bleeding, risk of patient removing, pressure bandage needed on removal
What are the two methods of direct BP monitoring and how do they work?
Arterial line, gold standard- catheter in dorsal pedal or femoral artery
Haemodynamic monitoring- electronic using fluid filled tubing with catheter detecting pressure waves in arteries, transducer detects movement and converts to electrical signal
What are advantages and disadvantages of indirect BP measurement?
Advantages- non-invasive, easier to run
Disadvantages- unreliable sometimes, less accurate, slower
What are advantages and disadvantages of doppler for BP measurement?
Advantages- inexpensive, efficient, can detect pulses in low flow states, fast results
Disadvantages- only provides systolic information
How does oscillometric BP monitoring work?
Artery wall oscillates as blood flows through as cuff inflates and deflates
Rapid increase in oscillation amplitude is systolic and rapid decrease is diastolic
What are advantages and disadvantages of oscillometric BP monitoiring?
Advantages- provides systolic, diastolic and mean information, automated process
Disadvantages- less reliable as affected by movement, cant pick up trends well in small animals, more expensive
What is the impact of incorrect cuff size when taking BP measurements?
Too big- artificially low result
Too small- artificially high result
How should you manage hypotension?
Find underlying cause and treat Reduce VA as vasodilatory Increase analgesia and local blocks Manage bradycardia Give fluids Ensure adequate ventilation
What is meant by SpO2?
Measurement of how much oxygen the blood is carrying as percent of maximum able to be carried
What checks should be made if SpO2 has fallen?
Check pulse oximeter is correctly working
Is patient intubated?
Is anaesthetic machines pressure gauges okay?
Is flow rate adequate?
Is breathing system correctly attached?
Are there any leaks in the breathing system or ETT?
Is the patient spontaneously breathing/are ventilator settings correct?
Does thorax expand if bag is squeezed or is there pressure or airway blockage?
Can lungs contract?
What are causes of lungs being unable to contract when SpO2 has fallen under GA?
Expiratory pathway blockage Twisted bag Closed APL valve Kink in tubing Blocked tube
If SpO2 is fallen but all checks are normal what is causing the problem?
Poor tissue perfusion
What are causes of abnormal breathing under GA?
Panting- inadequate anaesthesia
Paradoxical breathing- respiratory tract obstruction
What are some causes of no breathing when under GA?
Post induction apnoea
Too deep anaesthesia reducing respiratory drive
Too light anaesthesia causing breath holding
How do you identify tachycardia and bradycardia?
Monitoring pulses
Cardiac auscultation
What are common causes of tachycardia when anaesthetised?
Inadequate depth Hypercapnia Hypovolaemia Drug action Electrolyte abnormalities
What causes of tachycardia under GA in ASA 1 and 2 pateints?
Inadequate depth
Hypercapnia
How do you respond to tachycardia in response to inadequate depth of anaesthesia and what are signs this is the cause?
Increase depth of anaesthesia
Reaction to noxious and non-noxious stimuli, increased muscle tone, increased RR, increased BP, movement
How do you respond to tachycardia in response to hypercapnia and what are signs this is the cause?
Follow steps for when SpO2 falls
Poor respiration
How do you respond to tachycardia in response to hypovolaemia and what are signs this is the cause?
Stabilise before anaesthetic and manage fluid deficit
Patient is hypovolaemic or dehydrated
What should you do if suspect drug action is the cause of tachycardia under GA?
Rule out other causes
How do you respond to patients with electrolyte imbalances to prevent tachycardia under GA?
Identify on pre-assessment and stabilise
What is stage one of anaesthesia and what can be observed in this stage?
From induction to unconsciousness
Increased pulse rate and RR, may have breath holding and dilated pupils
What is stage 2 of anaesthesia and what can be observed in this stage?
Onset of unconsciousness until rhythmic breathing is present
All cranial nerve reflexes present, eyes wide and open with dilated pupils
What is plane 1 of stage 3 of anaesthesia suitable for and what can be observed in this stage?
Minor procedures
Regular and deep respiration, brisk pedal reflex (pinching paw), slowing and disappearing nystagmus (involuntary rhythmic eye movement), eyes pointing ventromedially
What is plane 2 of stage 3 of anaesthesia suitable for and what can be observed in this stage?
Most surgical procedures
Eyes ventromedial with partially separated eyelids, sluggish palpebral reflex (touching periocular skin), present corneal reflexes, relaxed muscles, lower pedal reflex, lower tidal volume, lower HR, lower BP
What is plane 3 of stage 3 of anaesthesia suitable for and what can be observed in this stage?
All procedures
Eyes face centrally and eyelids start to open, increased pupillary diameter, no pedal reflex, relaxed abdominal muscles, low HR, low BP
What is stage 4 of anaesthesia and what can be observed in this stage?
Overdose
Respiratory failure, rapid or slow pulses, eyes central, no palpebral reflex
What are caused of bradycardia under anaesthetic?
Too deep anaesthesia Drug action High vagal tone Hypoxia Hypothermia Hyperkalaemia
What are signs too deep anaesthesia is the cause of bradycardia and how do you respond?
Low RR, hypotension, low muscle tone, lack of reflexes
Adjust depth of anaesthesia
How do you respond when drugs are the cause of bradycardia during GA?
Treat with atropine if worried about hypotension or arrhythmia
What causes high vagal tone leading to bradycardia in GA and how is it treated?
Occulocardiac reflex- eye compression decreases pulse rate
Anticholinergics
How should you treat patient to prevent bradycardia under GA when pre-assessment picks up hyperkalaemia?
Stabilise before anaesthesia and treat underlying cause
What are causes of hypotension when under anaesthetic?
Reduced inflow to the heart, reduced pumping, vascular resistance due to drugs, hypovolaemia, shock, arrhythmia etc.
What are some causes of respiratory failure under anaesthesia?
Depression of brains respiratory centre
Impaired movement of thorax
Impaired lung movement
Airway obstruction
What is meant by cardiac arrest?
Cessation of effective circulation
What are possible causes of cardiac arrest?
Pre-existing CV disease Anaesthetic overdose Arrhythmia Hypovolaemia Electrolyte abnormalities Respiratory arrest
What are causes of hypertension under GA?
Nociception
Hypercapnia
Hypoxia
Drugs
How can you prevent vomiting in patients under anaesthesia?
Fast before anaesthetic
Elevate head until ETT cuff inflated
Consider omeprazole in patients with high risk
How do you respond to patients who vomit under anaesthesia?
Keep head down
Suction pharynx
What are risks of oesophageal reflux when under anaesthesia?
Excess or inadequate fasting
Drugs
Abdominal pressure
Abdominal surgery
What are causes of emergencies and accidents during anaesthesia?
Sick patients- stabilise before anaesthesia, prepare equipment and drugs
Human error, poor communication, not doing checklists, leaving APL valve open, drug admin errors, poor airway management, poor positioning, inadequate eye protection
Equipment failure
Poor preparation
Poor monitoring
Name drugs used for euthanasia and what species they are used for
Pentobarbital- lots of species
Secobarbital sodium plus cincocaine hydrochloride- dogs, cats, horses, cattle
What mode of action do euthanasia drugs act by?
Barbiturate enhances action of GABA at GABA receptor
Local anaesthetic blocks sodium channels in heart interrupting action potentials
Explain the general stages of recovery from anaesthesia
End of procedure so need to regain consciousness
Stop anaesthetic agent and antagonise injectable drugs either just before or after procedure ends
Give 100% oxygen if nitrous was used
Maintain analgesia
Remove airway device as appropriate
Place in suitable recovery area
What makes a suitable area to recover from anaesthetic?
Safe Secure Well ventilated Warm Easy to observe Good access to supplies
What should be observed in patients from extubation to full recovery?
Lift head
Sternal recumbency
Standing
No signs of sedation
How should you prepare for extubation?
Untie ties
Deflate cuff when close
When should you extubate dogs and rabbits?
Signs of laryngeal reflexes and spontaneous movement
When should you extubate cats?
Early reflexes, before laryngeal reflex
What happens if you extubate too early or late?
Early- unsupported airway
Late- distress, damage to airway, laryngospasm in cats
What factors need considering when recovering animals?
Drug factors and doses
Species, breed, age
Co-morbidities
CV function- delivery and distribution to kidneys
Hepatic and renal function- metabolism and excretion
Temperature- hypothermia causes slower metabolism and renal plasma flow
What parameters need monitoring when recovering animals?
TPR MM CRT Quality of recovery Pain Excretions Comfort Catheters Surgical site Food and water
What causes hypothermia in recovery?
Vasodilation from drugs
Lack of movement
Cold environment
What are the effects on recovery of hypothermia?
Bradycardia Cardiac arrhythmia Atrial fibrillation - 30 degrees Ventricular fibrillation- 24-38 degrees Impaired coagulation and wound healing Longer drug action so slower recovery Low oxygen delivery Slower metabolism
What causes hyperthermia in recovery?
Decreased heat loss
Warm environment
Increased metabolic heat production
What are the effects of hyperthermia in recovery?
Higher metabolic rate Higher oxygen requirement Cell damage Irreversible brain damage- 41 degrees Death- 43 degrees
What needs monitoring for respiration in patient recovery?
Patent airway
RR
Breathing pattern
What measures should you put in place to protect respiration in recovery?
If worried of aspiration or vomiting, keep head down
Remove water bowl to prevent drowning
Supplement oxygen where needed
How do you maintain a good quality of recovery?
Keep calm and stress free
Re-sedate if too excited
Be aware of causing injury
What are signs of pain in recovery?
Inappetence Immobility Vocalisation Agression Sleeping Increased HR Increased RR Increased temperature Increased BP
What does CPCR stand for?
Cardiopulmonary cerebral resuscitation
What are the mortality rates for patients who experience CPA?
Under anaesthesia- 53%
In general- 90%
What does RECOVER stand for and what is its purpose?
Reassessment campaign on veterinary resuscitation
Use evidence based guidelines to treating CPA and identifies areas that need more development
How should you prepare for a CPA?
Everyone involved knows what to do, what protocols are and where equipment, drugs etc. are kept
When should you initiate CPCR?
Unresponsive apnoeic patient with no pulses
What is classed as basic life support in CPCR?
Recognising CPA
Compressions- 100/minute 1/3 to 1/2 chest in lateral recumbency, compressing main part of heart and allowing full recoil
Ventilation- securing airway while compressions take place, 10 breaths/minute providing oxygen, can check effectiveness with capnography as hypoxia and hypercapnia reduce chance of circulation returning
What are roles in a CPCR team?
Lead Cardiac compressor Ventilator Note keeper Runner
What is classed as advanced life support?
Drugs- IV where possible
Correcting cause of arrest
Monitoring- ECG, capnography, pulse oximeter
Fluids, eye lubrication, temperature regulation, IV catheter placement
What is involved in post CPA care?
IVFT
Oxygen therapy
Referral where needed
Make sure CPCR process was correctly recorded
Why is it important to debrief after CPCR?
Emotions high
Discuss what happened
Clear the air of any problems
Restock equipment and drugs
How is CPA managed in already anaesthetised pateint?
Note time and inform surgeon Start compressions Manually ventilate Stop anaesthetic drugs and consider adrenaline Manage same as other crashes
What is a main contributor to pollution in veterinary practices and how does it contribute to global warming?
Anaesthetic gases
Greenhouse gases or plug atmospheric window (used to cool earth as low absorption of natural greenhouse gases)
Why is nitrous bad for the atmosphere?
Although less global warming effect has lower potency so more needs using, is also ozone depleting
How can practices improve carbon footprint?
Dont use nitrous Avoid unneeded anaesthesia Use TIVA where possible Sevoflurane is better than isoflurane Dont waste resources Low flow anaesthetic techniques
How does low flow anaesthetic work with circle and lack and what are negatives?
Circle- over 5kg, has reduced FGF. Can dilute anaesthetic, slower onset and hypoxic mixture if using for long time
Lack- under 5kg, uses capnography to find lowest FGF that prevents rebreathing
How should waste be disposed of in practice and what is the negative to reusing?
Correctly separated
Dont use unnecessary resources
Re-use and recycle where possible
Re-using has higher risk of infection and failure of equipment
What should be checked before sedation or anaesthetising horses?
Check passport (food producing so drug regulations)
Assess temperament to decide drugs
Assess CV and respiratory systems
Assess facilities, procedure and pain levels likely
Dont withhold food
Get owner consent, inform that best for vet to be present whole time
Describe the ideal environment for equine sedation
Quiet Calm Lots of time Safe Equipment and drugs prepared
How is equine sedation administered?
IV to jugular- ideal as fastest onset and most control of drug
IM- remote when cant gain IV access, need higher doses
What sedative are licenced in horses?
Acepromazine Xylazine Romifidine Butorphanol Buprenorphine Pethidine
What is the most common sedation combination used in horses?
Alpha 2 agonist and opioid
When is acepromazine used in equine sedation?
Alone or in combination to provide mild sedation
What is the onset time, length of effect, metabolism and any other effects of acepromazine in horses?
30 minute onset
4-6 hour duration
Metabolised by liver
Vasodilatory
What effects does alpha 2 agonists have in horses?
Sedation
Muscle relaxation
Analgesia
What side effects can alpha 2 agonists have in horses?
Bradycardia, second degree AV block so initially causes hypertension and vasoconstriction, then hypotension
Hypoinsulinemia
Decreased GI motility
What are the alpha 2 agonists used in horses for sedation?
Xylazine- shorter lasting, faster onset
Romifidine
Which opioids are used in horses for sedation?
Butorphanol- provides less analgesia
Buprenorphine- needs large volume
Pethidine- need to give IM, relieves colic
What effects do opioids have when given to horses for sedation in combination with alpha 2 agonist?
Synergistic effect on analgesia, increases sedation and ataxia (un coordination)
How should catheters be cared for in recovery?
Covered and suitably padded
Pressure placed on removal to prevent haemotoma
What are common causes of death in equine anaesthesia?
Fractures
Myopathy
Cardiac arrest
What are risk factors for equine anaesthesia?
Drugs Age Duration of procedure Type of procedure Environment (field or hospital)
What determines if horses are anaesthetised in field or hospital?
Temperament Can you get to hospital Type of procedure Length Facilities available
How should horses be prepared for general anaesthesia?
Full exam
Gained consent
Groom and remove shoes
Weigh
Antibiotics 30 minutes before anaesthesia if using to lower BP
Rinse mouth to prevent debris pushed into airway
IV catheter placed in left jugular
What equipment is needed for equine anaesthesia?
Padded head collar and lead rope Towel for eyes and eye lubrication Drawn up and labelled drugs ETT and gag prepared Table, monitors and machines prepared
How are horses induced for anaesthesia?
Once fully sedated
Ketamine/diazepam and thiopental in fast IV bolus
May use GGE/guaiphenesin, a muscle relaxant
Field- free fall guiding head
Practice- tilt tables and gates
What technique is used for equine intubation?
Blind technique, extend head and neck
Oral but can be nasotracheal
What maintainace is used for horses in field and theatre?
Field- TIVA for max 2 hours
Theatre- TIVA, sevoflurane, isoflurane
What are side effects of inhalational anaesthetics used in equine anaesthesia?
Respiratory depression
Hypotension
Rapid recovery
What analgesics are used for equine surgery?
NSAIDs- before anaesthetising Opioids Alpha 2 agonist Ketamine Local blocks
What should be monitored in equine anaesthesia?
RR and pattern- easily compromised leading to hypoxaemia, hypoventilation, hypercapnia as not designed to lay down for long times
Eye position, nystagmus- depth of anaesthesia
Palpebral reflex
Muscle tone
Movement- may be sudden
BP- CO decreased in anaesthesia, commonly get hypotension
ECG- common to initially get 2nd degree AV block
How should you recover horses from anaesthesia?
Quiet environment
Cover eyes to reduce stimulation and fear
Supplement oxygen
Remove ETT when respiratory effort increases (weak laryngeal reflexes)
Alpha 2 agonist to keep calm
Analgesia
Catheterise bladder to remove stimulation to stand
What are causes and prevention of equine post anaesthetic myopathy?
Causes- damage during anaesthesia
Prevention- careful positioning, let down (take out of training) fit horses few days pre-op, minimise anaesthetic time, lighter anaesthesia, avoid hypoxia
What are signs of equine post anaesthetic myopathy?
Lameness Cant stand Distress Hard swollen muscles Myoglobinuria High creatinine kinase muscle enzyme
What is treatment for equine post anaesthetic myopathy?
Analgesia Sedation Fluids Nursing care May need euthanasia
What are common neuropathies/nerve compression in horses after anaesthesia and what are the prognoses?
Radial, facial and femoral, brachial plexus
Depends on degree of damage
What is spinal cord malacia?
Softening of spinal cord
What are causes, signs and result of spinal cord malacia?
Cause- unknown
Sign- complete hind limb paralysis
Result- fatal
What are common causes of fractures in equine anaesthesia?
Trauma in induction, recovery
Pre-existing injury
Myopathy increases risk
When is equine castration carried out typically?
6 months to 2 years
Testicles fully descended
Where can equine castration be carried out and how?
In hospital or field by vet
Standing or under GA
Why are horses castrated?
Behaviour modification- reduced agression, easier to handle geldings
Management- turn out with mares
Control breeding
Medical reasons- neoplasia etc
What determines if a castration is done standing or under GA?
Size of horse for visualisation
Temperament
Cost
What is an open castration?
Vaginal tunic incised and left open
When are open castrations carried out?
Young unbred horses when being castrated standing in field
How is an open castration performed?
Incision through skin and vaginal tunic to expose testes
Emasculators used on vas deferens and testicular vessels to crush and transect
What is semi-closed castration?
Vaginal tunic incised then sutured closed
What environment is semi-closed and closed castration carried out in?
Hospital under GA
What is closed castration?
Vaginal tunic sutured proximally to testes before incision
How is closed castration performed?
Incision through skin only with blunt dissection of vaginal tunic containing testes
Ligatures placed before emasculation
What are options for the scrotum following castration?
Primary closure- sutured
Secondary closure- left open, used in field
May need ablation
What are advantages and disadvantages of standing castration?
Advantages- quick, effective, cheap in well handled young horses
Disadvantages- poor asepsis, commonly get minor complications, risk to surgeon
List equipment needed for standing castrations?
Sedation Local anaesthetic Analgesia Antimicrobials Gloves Scrub Swabs Needles and stitch kit Scalpel Emasculators Ketamine and IV prepared if GA is needed
What is the general process for preparing for standing castrations?
Sedate Check 2 testicles present Scrub Inject local anaesthetic into subcutis and testicle Rescrub
How should horses be positioned for GA castration in hospital or field?
Hospital- dorsal or lateral recumbency
Field- lateral recumbancy
What are some common post-castration complications in horses?
Swelling
Bleeding
Infection- scirrhous cord/infection of spermatic cord remnant, staphylococcal infection
Tetanus
Evisceration- prolapse of omentum or intestine through inguinal ring, intestine is emergency
What needs to be monitored post-castration in horses?
Bleeding- drips normal for 12 hours
Swelling- shouldn’t be more than original size
Surgical site- check for protrusions
Sedation- may cause colic, monitor appetite etc
How do you manage horses after castration?
Box rest for 24-48 hours Walk 2-3 times daily after 2 days to reduce swelling and encourage drainage Turn out after 7-10 days NSAIDs Fertile for 2 months
What is cryptorchidism and how is it detected?
Failure of testicular descent
Inguinal palpation, ultrasound, blood tests, surgical exploration
How is cryptorchidism treated?
Laparoscopic cryptochidectomy
What are potential causes of higher mortality rates in exotics under anaesthesia?
May lack history
Pre-existing diseases may be unrecognised
Small to hard to weigh accurately, examine, place IV
Completely different anatomies
Handling causes high stress
Equipment not suitable
What parts of the patient to be considered in exotic anaesthesia?
Eyes- protuberant risks damage, corneal dissection
Pharyngeal pouch- needs emptying before intubation
Mouth- hard to intubate if large incisors, narrow jaw, obstructive pharyngeal tissue
Physiology- metabolic rate, rate of glucose and oxygen consumption
Temperature- high SA:V ratio
Respiratory system- hard to auscultate
GI system- diet, rabbits cant be starved
Species specific- drug concerns, diseases, husbandry
What factors need considering for birds when anaesthetising?
Wide range of species
Hide illness
Handling causes stress, if too tight stops breathing as sternum cant move
Prone to hypothermia and hypoglycaemia
Hard to intubate as small and cant cuff as complete tracheal rings
Muscle relaxants majorly affect completely active respiration
Low HR
High metabolic rate
What factors need considering for reptiles when anaesthetising?
Can carry zoonotic disease on surface Ectothermic Free moving organs Breath hold Only open larynx in active respiration 1 heart ventricle Long soft palette making intubation hard Lower oxygen consumption Snakes have single functional right lung Cant cuff as complete tracheal rings No muscular diaphragm so other muscles needed to respire such as tortoises limbs Cant regurgitate
What are recommended pre-op starvation for exotics?
Rabbits/rodents- none Guinea pigs- up to 4 hours, empty pharyngeal pouches Ferrets- 6 hours Reptiles- none, avoid live insects Birds- species dependent
What anaesthetic breathing equipment may be needed for exotic anaesthesia?
T-piece Gas chamber Mask ETT V-gel
List routes of admin of drugs to exotics
IV- basilic, medial tarsal, right jugular
IM- pectoral
IP
SC
IO- cranial tibiotarsus, ulna (high risk of pain and infection)
Inhalation
Oral
What are signs of acute and chronic pain in exotics?
Acute- escape attempts, avoidance, agression, restlessness, increased respiration
Chronic- immobility, agression
What parameters are monitored for exotics under anaesthesia to assess depth?
Rightwing reflex- ability to correct orientation of body by vestibular system, only when light
Withdrawal reflex
Jaw tone
Pulses
What equipment can be used to monitor exotics under anaesthesia and how can it be adapted to be better suited?
Pulse oximeter- foot or tail base instead of tongue
Capnograph- mainstream to prevent reducing FGF
ECG- cut down pads, use needle electrodes
Doppler
Temperature- rectal, small probe
