Anaesthesia Flashcards
What occurs in the pre-op phase of anaesthesia?
Owner consent and admission to practice Full exam/history, ASA classification and planning stage Set up machine/equipment Prepare meds/drugs/fluids Premed patient
What happens in the induction phase of anaesthesia?
IV catheter placement
Pre-oxygenation
Admin of induction agent
Security of airway
What happens in the maintenance phase of anaesthesia?
Maintain anaesthesia - gas/TIVA/injectable
Placement of local/regional blocks
Continue to surgery/diagnostics
What happens in the recovery phase of anaesthesia?
Cessation of gaseous maintenance/CRIs
Antagonism of injectable drugs
Removal of airways device
Move to recovery area
What is the anaesthesia triad?
Analgesia
Narcosis
Muscle relaxation
What did the CEPSAF enquiry discover?
50% of deaths occurred within 3 hours of recovery
Sick animals had higher risk than healthy ones
Risk significantly higher with GA than sedation
Cats had twofold increase in risk
What are the species-specific problems seen?
Extremes of size Hyper-/hypothermia Aggression/risk of injury Drug sensitivities in breeds Obesity
List some breed-specific problems with anaesthetic drug use.
Brachycephalic
Boxers = ACP / cardiomyopathy
Collies/sheepdogs/shepherds = MDR1 gene
Greyhounds = lack of cytochrome P450 / body fat
Dobermann = Von Willebrand factor / dilated cardiomyopathy
Miniature schnauzer = females sick sinus syndrome
What can VNs do/not do in terms of inducing/maintaining anaesthesia?
Can administer a specific amount of meds directed by VS / act as VS hands to maintain
Cannot admin meds incrementally or to effect
What information needs to be gathered from an owner during the pre-op assessment?
Full history Owner questioning - any concerns? Previous reactions to drugs? Breed/species Confirm pre-op fasting times
What is assessed in the pre-op clinical examination?
MMs/CRT Thoracic auscultation Heart murmur? Pulse quality and effort Ventilatory effort Temperature Swellings/distension Temperament
What is the goal of pre-op fasting?
To reduce the volume of the stomach contents
To prevent GOR/regurgitation and aspiration
What are the recommended guidelines for pre-op fasting?
Cats = 6-8 hours
Dogs = 8-10 hours
Rabbits/small furries = no starvation but may withhold food ~30 mins pre-op
What diagnostic tests may be run prior to anaesthesia induction?
Bloods Urine Radiography ECG Echocardiology Ultrasound
What are the injectable anaesthetic agents and what animals are they licensed for?
Propofol - dogs, cats
Alfaxalone - dogs, cats, rabbits
Ketamine - horses, dogs, cats
Tiletamine / zolazepam - dogs, cats
What are the injectable drugs for euthanasia?
Pentobarbital Secobarbital sodium (quinalbarbital sodium) plus cincocaine hydrochloride = Somulose
What factors affect the effect of anaesthetic injectables?
Blood flow to brain Amount of non-ionised drug Lipid solubility Molecular size Conc. gradient Protein binding Distribution Metabolism Excretion
What makes the ideal injectable anaesthetic agent?
Rapid onset Non-irritant Minimal cardiopulmonary effects Rapid metabolism and elimination Non-cumulative Good analgesia Good muscle relaxation
What are the key points regarding propofol as an injectable anaesthetic?
Rapid onset of action Highly plasma protein bound (96-98%) and lipid soluble Rapidly metabolised and eliminated Non-cumulative in DOGS No analgesia Fair muscle relaxant Non-irritant Post-induction apnoea, hypotension, Heinz body anaemia in cats
What are the key points regarding alfaxalone as an injectable anaesthetic?
Non-irritant (?IM) 20% plasma protein bound Rapid onset Rapid metabolism and elimination Non-cumulative Preserves baroreceptor tone Some respiratory depression
What are some key points regarding ketamine as an injectable anaesthetic?
Poor muscle relaxation (not used as sole agent) Reflexes maintained Maintains CVS/respiraotyr function Analgesia/antihyperalgesia Slow onset Non-cumulative 50% plasma protein bound Increase intraocular-/intracranial pressure
What factors affect recovery from injectable anaesthetics?
Drug factors, e.g. dose
Species, breed and age
Co-morbidities, e.g. CVS/hepatic/renal function
When is TIVA useful and what are its ideal properties?
Used to reduce exposure to inhalants, or “in the field” when machines are not available
Ideal properties = rapid metabolism and elimination, fast onset, high therapeutic index, pharmacokinetics available
In which three ways can anaesthesia be induced by injection and what are the advantages/disadvantages of each?
IV = quickest onset (2-10mins), reliable, less stress BUT relies on IV catheter - IV only for Propofol/Alfaxalone
IM = fairly quick (10-20mins), reliable if actually IM BUT can be painful, slower onset
SC = easy to administer, less painful than IM BUT can cause pain, longer onset (30-45mins), lower efficacy
Which two ways can anaesthesia be induced through inhalation and what are the advantages/disadvantages?
Chamber inductions = easy to set up/use, cheap, no technical skill BUT very stressful, difficult to observe patient, risk of exposure
Face masks = cheap, easy to set up/use, can give oxygen/VAs quickly BUT does not protect airway, increases dead space, risk of exposure
Describe the laryngeal mask airway (LMA).
Easy to use - sits over airway
Reduced complications compared to ETT
Reduced airway pollutants compared to face mask
Not really designed for veterinary species
Describe the supraglottic airway device (V-GEL).
Species specific / weight specific design
Training needed before use
Describe ET tubes.
Allows airway protection
Prevents atmospheric exposure
Allows accurate provision of anaesthetic agents
Some have a cuff system
What is the point of a cuff on an ET tube?
Allows a tight seal in the trachea Prevents gas leaking around tube Prevents contents going into patient lung Allows accurate delivery of VAs/oxygen Allows direct route to lungs
What equipment should you prepare for ET intubation?
Laryngoscope Tubes - range of sizes (length = incisors to shoulder tip) Local anaesthetics (cats) Tie Cuff syringe Swab/suction/mask for preoxygenation
What are the common complications during induction?
Injury - us or them Lack of airway patency Aspiration/regurgitation Hypothermia CVS/respiratory system dysfunction Post-induction apnoea
List the patient safety features on anaesthetic machines.
Pin-index system and NIST for pipelines Colour-coded pressure gauges and flowmeters Oxygen flowmeter "touch coded" Ratio regulators Nitrous oxide cut-out Alarm whistle Air intake valve Reserve oxygen cylinders
What is the difference between active and passive scavenging?
Active = waste gases/anaesthetic agents drawn outside of building by a fan and vent system, requires an air break to prevent negative pressure being applied to patient breathing system
Passive = gas is pushed by patient expiratory effort into tubing either into tubing leading outside of building or into a canister containing activated charcoal
What makes the ideal inhalational agent?
Non-irritant Minimal effects on CVS and respiratory function Rapid uptake and elimination Non-toxic Non-flammable and chemically stable Easily vaporised Good analgesia and muscle relaxation
Define MAC and what factors can affect it.
MAC = Minimum Alveolar Concentration
Reduced by: other drugs (e.g. premed), hypothermia, pregnancy, geriatric/neonatal animals, hypothyroidism
Increased by: hyperthermia, young animals, hyperthyroidism, admin of catecholamines/sympathomimetics
How can we reduce exposure to inhalant anaesthetic agents?
Well-ventilated theatres/recovery areas (15-20 air changes)
Use IV induction agents where possible
Use cuffed ET tubes
Connect animal to breathing system before turning on gases
Use low flows
Check for leaks
Flush breathing system with oxygen before disconnecting animal
Use key fill vaporisers
Define vapour.
Vapour = gaseous state of a substance that at ambient temp. and pressure is a liquid.
Define partial pressure.
Partial pressure = pressure that individual gas exerts in a mixture of gases.
Define partition coefficient.
Partition coefficient = ratio of the concentration of a compound in two solvents at equilibrium.
What are the disadvantages of using IM injectable anaesthetics?
Difficult to control depth - slow onset and unpredictable
Limited access
Limited range of drugs
What are the disadvantages of IV injectable anaesthetics?
Can result in unstable plane of anaesthesia - bolus techniques
Can get cumulative effects of some drugs
What are the advantages/disadvantages of inhalational anaesthetics?
A = easy to administer/calculate, suitable for most patients, easy to adjust depth D = requires specialist equipment, has impact on BP through vasodilation, personnel risks
What are the advantages/disadvantages of injectable anaesthetics?
A = available in all settings, can be administered by a nurse, provides good level of sedation D = careful dosing needed, limited choice of drugs, not so easy to change depth quickly if at all
What factors help us decide which maintenance technique to use?
Species Behaviour Procedure Facilities Expertise Budget
What must we consider when positioning patients for anaesthesia?
Prevent muscle/nerve damage Prevent post-op pain Optimise ventilation Nasal congestions Protect eyes, apply ocular lubricant-opioids
What are the four ways in which heat can be lost during anaesthesia?
Convection - loss of body heat to cool air surrounding body
Conduction - loss of body heat to surfaces that in contact with body
Radiation - loss of body heat to structures not in contact with body
Evaporation - loss of boy heat from moisture evaporation
What effects can hypothermia have?
CNS depression Hypotension Bradycardia Hypoventilation Decreased basal metabolic rate Decreased urine output
How can we reduce the risk of hypothermia?
Keep anaesthetic time minimal Minimise wetting of patient/fur Maintain a high ambient temp. Use heat and moisture exchangers Use appropriate breathing systems Use warmed fluids for IVFT Keep patient warm from point of premed Use insulating materials
Describe Stage 1 of anaesthesia.
Begins at time of induction and lasts until unconsciousness.
Pulse and resp. rates elevated
Breath-holding can occur
Pupils may dilate
Describe Stage 2 of anaesthesia.
Lasts from onset of unconsciousness until rhythmic breathing is present
All cranial nerve reflexes present and may be hyperactive
The eye may appear wide and open and pupil dilated - soon rotate to ventromedial position
Describe Plane 1 of Stage 3 of anaesthesia and what it is suitable for.
Respiration becomes regular and deep
Spontaneous limb movement is absent, but pinch reflex may be brisk
Nystagmus, if present, will start to slow and disappear
Eyeball is ventromedial, opening the eye will show the sclera
This plane is suitable for minor procedures e.g. abscess lancing, skin suturing
Describe Plane II of Stage 3 of anaesthesia and what it is suitable for.
Eye position ventromedial and eyelids may be partially separated
Palpebral reflex is sluggish or absent, although corneal reflexes persist
Muscles appear relaxed, pedal reflex begins to go
Tidal volume may decrease as resp. rate settles/HR and BP may be slightly reduced
This plane is suitable for most surgical procedures
Describe Plane III of Stage 3 of anaesthesia and what it is suitable for.
Eyeball becomes central and eyelids begin to open
Pupillary diameter increases
Pedal reflex is lost and abdominal muscles are relaxed
HR and BP may be low
This plane is suitable for all procedures
Describe Stage 4 of anaesthesia.
Overdose!
Characterised by progressive respiratory failure
Pulse may be rapid or very slow and become impalpable
Eye may become central with no palpebral reflex
CRT prolonged
Sometimes accessory respiratory muscle activity, indicated by twitching in throat - this may mimic inadequate anaesthesia
What are the pros and cons of both indirect/non-invasive methods of measuring arterial BP?
Doppler = inexpensive, efficient, detects pulse flow in low flow states, good in cats, quick results BUT systolic only
Oscillometric = systolic, diastolic and MAP BUT less reliable, interference/movement, not so useful in small animals, more expensive
Define systolic, diastolic and mean arterial pressure.
Systolic = a measure of the force the heart exerts on the walls of the arteries Diastolic = the pressure in the arteries when the heart is between contractions Mean = the intravascular pressure in the vessel during one complete cardiac cycle
How does a Doppler machine work?
Emit an ultrasound signal
Produce auditory signal generated by frequency shift of underlying RBCs
An inflatable cuff is placed around limb
The cuff is inflated
At some point, the noise will stop (as flow stops)
The BP is the measured point when flow returns
Which vessel is most commonly used for direct/invasive BP measurements and why?
Metatarsal/dorsal pedal artery
Easy to secure in place
Easy to maintain for post-op monitoring
Less risk of a large haematoma
How does a haemodynamic monitoring system work?
Electronic system with fluid-filled tubing
Catheter detects pressure waves in arterial system
Fluid column in tubing system carries pressure wave to diaphragm of electronic transducer
Converts to an electrical signal
Monitor indicates arterial BP
What should we do if faced with a low BP?
Identify underlying cause! Try reducing volatile agent Consider concurrent use of local blocks/topping up analgesia Manage bradycardia Consider fluids/drug therapy
What information do we gain from capnography?
Inspired carbon dioxide (numerical value)
Expired carbon dioxide (numerical value)
Respiratory rate (numerical value)
Capnograph (waveform)
What are the pros and cons of side stream capnography?
Pros = cheaper, less likely to break, easy to replace if it does break Cons = not quite real time, takes some FGF requirement, sample line can get easily damaged and needs changing regularly
What are the pros and cons of mainstream capnography?
Pros = real time results, no need for sample line = no requirement for FGF Cons = very expensive to buy, can be damaged easily = £££, can add drag to system
Describe a capnograph waveform.
Baseline (should always return to this) Expiration (Alpha angle = ventilation perfusion of lungs) Alveolar plateau (where gas is sampled) (Beta angle = rebreathing) Inspiration
What are the ideal values from a capnograph?
End tidal CO2 (ETCO2) = dogs 35-45mmHg, cats 28-35mmHg Inspiratory CO2 (INCO2) = all species 0
What can cause a high ETCO2?
Hypoventilation
Reduced resp. rate
Reduced tidal volume
What can cause a low ETCO2?
Hyperventilation Low cardiac output Decreased metabolic rate Hypothermia Pulmonary embolism Leak in sampling line Poor sampling technique (dilution) Leak in breathing system
What can cause a high INCO2?
Non-rebreathing system = too low FGF, too much dead space
Rebreathing system = exhausted absorbent, faulty/sticky valves
On what lead do we run anaesthesia ECG?
Lead II.
How do we attach ECG leads to small animals?
Red = right fore Yellow = left fore Green/black = left hind
What do each part of an ECG trace show us?
P wave = atrial depolarisation
QRS complex = ventricular depolarisation
T wave = ventricular repolarisation
What information will a pulse oximeter give you?
Haemoglobin oxygen saturation levels (%)
Heart/pulse rate (numerical value)
Some machines give a waveform
How does a pulse oximeter work?
Light absorption, differentiation of wavelengths
Probe = light emission from one side (red light/infrared), light detector on other side
Oxyhaemoglobin - absorbs greater amounts of infrared and lower red light
Deoxyhaemoglobin - absorbs more red light than oxyhaemoglobin
Where can we position a pulse ox probe?
Hairless and unpigmented - tongue, inter-digital, ear, prepuce, vulva, skin webbing
What are the benefits of pulse oximetry?
Non-invasive Available in almost all settings Non-painful Quick and easy to set up and use Gives a clear reading Can be used on conscious and unconscious patients
What are the limitations of pulse oximetry?
False readings
Susceptible to damage
Doesn’t work well in anaemia
Can cause tissue compression in small animals
Patient movement
Poor perfusion (hypothermia, shock, vasoconstriction)
Too thin tissue (e.g. cat ear)
Interference
No differentiation between oxyhaemoglobin and carboxyhaemoglobin
When do we extubate dogs/rabbits?
Watch for signs that laryngeal reflexes are returning
Watch to see if other reflexes returning and/or spontaneous movement
When do we extubate cats?
Have very sensitive larynxes so danger of laryngospasm if you wait for swallowing
Need to extubate before this point - earlier reflexes e.g. ear flick / blink
When is late extubation appropriate?
May be necessary in patients at high risk of airway obstruction, e.g. brachycephalic dogs
NOT suitable in cats due to risk of laryngospasm
Will need to monitor patients carefully
What are the patient’s stages of anaesthetic recovery?
Extubation Lift head Assume sternal recumbency Stand Full recovery with no signs of sedation/ataxia
What can be the physiological signs of pain in recovery?
Heart rate
Respiration rate
Temperature
Blood pressure
What behaviour changes should we watch for in recovering patients?
Inappetence Reluctance to stand/move / difficulty in mobility Vocalisation Panting Lip-smacking Aggression Sleeping more Reacting badly to being touched
What other considerations for patient comfort should we have in recovery?
Full bladder Cold / hot Wet bedding Tight stitches Clipper rash Need to defecate Fear/anxiety
How do we conduct post-op feeding in recovery?
Feed when awake/able to stand and swallow, unless GI surgery/sedation/CRIs/follow-up imaging
Bland, soft food
Little and often
Assisted feeding in smalls e.g. rabbits
