SA Anaesthesia Flashcards
How common is anaesthetic related mortality in healthy dogs, cats, rabbits and horses?
Dogs: 0.05%
Cats: 0.1%
Rabbits: 0.7%
Horses: 1%
What risk factors are there for perianaesthetic mortality?
Pre-existing disease (main one)
Overweight/underweight
Procedure urgency and duration
Emergency procedures
5 day 1 anaesthetic skills?
- Ensure patent airway
- Give oxygen
- Know how to apply IPPV
- IV catheter and giving IV drugs
- Basic CCPR
ASA statuses for anaesthesia?
ASA 1: normal healthy animal
ASA 2: mild systemic disease
ASA 3: moderate systemic disease
ASA 4: severe systemic disease, constant life threat
ASA 5: moribund, not expected to survive following 24h
What are the 3 aims of anaesthesia?
Unconsciousness
Analgesia
Muscle relaxation
Which of the following anaesthetic drugs give analgesia, sedation, unconsciousness and muscle relaxation?
ACP Benzodiazepines A2 agonists Opioids Barbiturates Ketamine Propofol Inhalationals N2O Local anaesthetics
Analgesia: - a2 agonists - opioids - ketamine - N20 - local anaesthetics Sedatives: - ACP - a2 agonists - opioids Unconsciousness: - barbiturates - ketamine - propofol - inhalationals Muscle relaxation: - ACP - benzodiazepines - a2 agonists - barbiturates - propofol - inhalationals
What is balanced anaesthesia? Why used?
Using 2 or more agents to provide anaesthetics
Reduces doses of each drug, reduces side effects and optimises analgesia
Define sedation?
Mental calming/sleeping and disinterest in environment/decreased responsiveness to stimuli
Purpose of a premedication?
Relieve anxiety Smooths induction, maintenance and recovery Anaesthetic sparing effects Pre-emptive analgesia Reduces muscle tone
Uses of sedation?
Premedication
Chemical restraint
Analgesia
Reduce muscle tone
ACP: Type of drug? What used for? What used alongside? How does it work? Does it give analgesia? Onset of action? Duration? Side effects? Patients to be careful with?
Type: Phenothiazine
Action:
- mental calming due to dopamine antagonism
- potentiates CNS depressant effects of other agents
Use:
- commonly used as a premed, often with opioids
- no analgesia
- not reversible
Onset and duration:
- 30-40 mins for mental calming
- 4-6h duration
- unpredictable sedative
Side effects:
- vasodilation and hypotension
- syncope (CV collapse due to hypotension and bradycardia, esp. brachycephalics)
- pharyngeal muscle relaxation (problem in brachycephalics)
- hypothermia
- at high doses, can cause excitation
Be careful with:
- cardiovascularly compromised patients
- brachycephalics
- very excited animals
- paediatric patients (CV effects more risky)
- breeding stallions
- epileptics (may lower seizure threshold)
Azaperone: Type of drug? How it works? When used? When to be careful? Side effects?
Type: butyrophenones Action: - antidopaminergic and anti-adrenergic effects in reticular activating system of CNS Use: - pigs Side effects: - penile prolapse in boars if large doses - hypothermia Be careful with: - brachycephalic pigs
A2 agonists: Uses? How it works? Is there any analgesia or muscle relaxation? Reversible? Side effects? What to be careful with?
Uses: - sedation and premed - predictable, dose dependent sedation How it works: - suppresses activity in reticular activating system - a2 agonism in the locus coeruleus in brainstem - analgesia (shorter duration than the sedation) and muscle relaxation - reversible (atipamezole) Side effects: - initial hypertension and peripheral vasoconstriction -> reflex bradycardia -> relaxation of peripheral vascular tone -> BP stabilises - significant reduction of cardiac output - sinus arrhythmia, SA block, AV block - diuresis - hyperglycaemia - GI effects - sweating - hypoxaemia with high doses - suppression of thermoregulation Care with: - absorbed across mucous membranes - animals with CV disease/compromise - sick/debilitated patients - patients with diabetes mellitus - patients with laryngeal dysfunction - small ruminants
Benzodiazepines: Uses? How it works? Does it give analgesia and muscle relaxation? Side effects? Reversible? Care? Licensed?
Uses: - unreliable sedation in healthy animals - useful in 'at risk' patients - anti-convulsant - often used for induction with other agents Action: - GABA-specific benzodiazepine binding sites in brain and spinal cord - central muscle relaxtation - no analgesia - reversible with flumazenil or surmazenil Side effects: - minimal CV depression - at high doses, midazolam will cause greater CV depression than diazepam - minimal respiratory depression - enhances depression of other drugs Care with: - diazepam binds to some plastics - postural muscle weakness (can't use for large animals as this makes them panic) - care if hepatic disease None licensed
Opioids: Uses? Analgesia? Action? Reversible? Analgesia?
Uses: - potent, effective analgesia - poor sedation (can be used for low level sedation of severely compromised patients) Action: - bind to opioid receptors - reversible Side effects: - resp, GI, CV
Advantages and disadvantages of injectable induction agents?
Advs: - not much equipment needed - generally rapid and smooth - no environmental poolution Disadvs: - can't retrieve - need accurate weight/good estimate - CV and respiratory depression
Propofol: Use? Benefits? Side effects? What to be aware of with cats? When to be careful?
Use: induction Benefits: - rapid and smooth - not often painful - twitching not common Side effects: - vasodilation with no compensatory increase in HR (reduces CO) - post-induction apnoea - negative inotrope Cats: - repeated doses are cumulative (takes a couple of days to remove from body) - potential for Heinz body anaemia (oxidative damage to RBCs) Careful with: - cardiovascularly compromised patients
Why does propofol cause post-induction apnoea? What to do if happens/to compensate?
Increases the level of CO2 allowed before brain signals to breathe (to about 60mmHg)
Can use IPPV
Pre-oxygenate for 5 mins via mask before induction to compensate
Alfaxolone: Use? Side effects? Benefits? When to be careful?
Use: induction
Side effects:
- vasodilation with compensatory increase in HR
- post-induction apnoea (less than propofol)
- less smooth than propofol
- more twitching than propofol (avoid in seizure patients)
Benefits:
- cardiac output maintained better than propofol
- non cumulative in cats
- can give IM or IV
Ketamine: Uses? How it works? Side effects?
Use:
- induction (main induction agent for horses)
- analgesia (can use lower dose alongside propofol/alfaxolone for analgesia)
- often given IM as part of ‘triple combination’ in cats
Action:
- NMDA antagonist
Side effects:
- increases sympathetic tone -> vasoconstriction
- direct negative inotrope (in normal animal, CO stays the same due to opposite effects of vasoconstriction and negative inotropy)
- post-induction apnoea (often breathe again after giving one breath)
- muscle rigidity (use with drug which gives muscle relaxation e.g. benzodiazepine)
- excessive salivation in dogs and cats
- often keep cranial nerve reflexes so hard to tell how asleep
Etomidate: Use? Benefit? Side effects?
Use: - induction - but not often used/available Benefits: - only agent with virtually no CV effects - good for CV compromised patients Side effects: - stops adrenal glands working
Is thiopental used in smallies? Why?
No (just horses as only drug able to use at sensible volume when horse too light on table)
CV effects - arrhythmias etc
Advantages and disadvantages of inhalation agents for induction?
Advs: - doesn't require IV access Disadvs: - prolonged induction time - distress - airway irritation - environmental pollution - requires tight fitting mask or chamber - increased risk of death
Avoid unless have to use!
Sevo better - smells nicer, breathe better, quicker, reduced chance of death
Which is the only induction agent with true analgesia?
Ketamine
Advantages and disadvantages of inhalation agents for maintenance of anaesthesia?
Advs: - also delivers oxygen - can ventilate if required - easy to alter anaesthetic level - easy to remove from animal - low running costs Disadvantages: - expensive equipment - cannot deliver without specialist equipment - must have an airway
Advantages and disadvantages of intravenous agents for maintenance of anaesthesia?
Advs:
- no need for a lot of specialist equipment
- bolus or TIVA
- may be better for some types of problem
Disadvs:
- cumulative effect -> prolonged recovery, slower changes in depth
- doesn’t deliver oxygen
- can’t be easily removed
- drugs can be expensive
What is MAC?
= Minimal alveolar concentration
The alveolar concentration a which 50% of patients will respond to a standard noxious stimulus
Majority of animals should be adequately anaesthetised at 1.2-1.5 x MAC (if need more, likely not enough analgesia or leak)
What affects MAC?
Species Age Hypoxia Profound hypotension Temperature Circulating catecholamines Pregnancy Other drugs
Nitrous oxide: Advs? Disadvs?
Advs: - some analgesia - few CV/resp side effects - cheap Disadvs: - potentially teratogenic - moves into gas filled spaces - can make colic/pneumothorax etc worse (care in ruminants)
Side effects of isoflurane and sevoflurane?
Vasodilation
Respiratory depression
Why monitor anaesthesia?
Maintain physiology Maintain adequate anaesthetic depth Prevent patient suffering from pain Safety to personnel Legal implications
How to monitor the CNS system during anaesthesia?
Palpebral and anal reflexes: brisk -> sluggish -> absent
Eye position: central -> ventral -> central
Pupil: constricted when awake -> dilated -> constricted -> dilated (deep)
Lateral nystagmus = light (or ketamine_
Lacrimation
Changes to autonomic tone:
- sweating
- CV changes
Muscle tone:
- tension in tendon of sternocephalicus
- jaw tone
Movement = very light or about to die (flexor muscles)
How to monitor the CVS during anaesthesia?
Pulse/HR
Pulse quality (subjective)
Feel peripheral pulse for indication of perfusion
Mucuous membrane colour - indicates oxygenation and perfusion
CRT:
- <1s = poor perfusion or hypovolaemia
- >2s = maldistributive shock
Normal HR under anaesthesia for dogs, cats and horses?
Dogs: 50-120
Cats: 60-140
Horses: 24-40
Normal systolic, diastolic and mean BP under anaesthesia for dogs?
Systolic: 80-130
Diastolic: 40-60
Mean: >60
Differences between invasive BP and non invasive BP?
Invasive (IBP):
- continuous readings, have SBP, DBP and MAP
- invasive/risk of infection
- allows arterial blood sampling for blood gases
- more expensive equipment
Non invasive (NIBP):
- intermittent readings, may only get SBP or MAP
- no risk of infection
- need correctly fitting cuffs or inaccurate values
What is pulse oximetry? What level is normal?
Measures % saturation of oxygen of Hb (SpO2)
Also measures pulse
Indirect indication of perfusion (plesthysmograph)
Normal: 97-99%
Be concerned if <95%
Limitation of pulse oximetry?
Affected by: - hypotension/vasoconstriction - bright light - non pigmented mucosa - movement Probe may blanch capillary bed
What is capnography? Normal level? Other uses?
Measures EtCO2 Normal: 35-45mmHg >60 = hypoventilation <35 = hyperventilation Other uses: - checks correct placement of ETT - confirms pulmonary circulation - indicates problems e.g. with breathing system
On which parts of the pain pathway do NSAIDs, opioids, local anaesthetics, NMDA antagonists, Ca channel blockers and tramadol work?
Local anaesthetics just nerve terminal
NMDA antagonists, Ca channel blockers and tramadol: dorsal horn of spinal cord and brainstem-cerebellum
NSAIDs and opiates all 3
NOLANP?
NSAIDs Opioids Local anaesthetics A2 agonists NMDA antagonists Paracetamol
When to not use NSAIDs for short term anaesthetic analgesia?
If think animal may be/become hypotensive (-> reduced renal perfusion)
How do protein binding and vasodilation affect the duration of action of a drug?
Increased protein binding = longer duration
Vasodilation = shorter duration
What increases potency?
Increased lipophilicity
Small size
What toxicities do lidocaine and buipvacanine have?
Lidocaine: - respiratory depression - seizures Bupivacaine: - cardiotoxicity (don't use IV)
Paracetamol: Licensing? Can you use it alongside NSAIDs or steroids? Contraindications?
Licensed in dogs in combination with codeine
Can use with NSAIDs or steroids (despite data sheet)
Not cats!!! Can’t glucoronidate so makes toxic metabolite
Define pain?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage
What are the 4 parts of the pain pathway?
- Transduction by nociceptor: convert stimulus to nerve impulse
- Transmission by sensory nerve fibre: transmit impulse to brain
- Modulation by spinal cord: ensure pain perceived is proportional to stimulus
- Perception by brain: perceive pain in the brain
Differences in speed of primary afferent axon types for pain? Why is there a difference?
Aa AB: fastest Ad: second fastest C: slowest Due to different amounts of myelination (C fibres are unmyelinated, Aa most myelinated)
Difference in myelination, speed, type of pain and which stimuli elicit the pain, between Ad and C fibres?
Ad: - myelinated - fast pain - sharp, brief pain - well localised - elicited by mechanical or thermal stimuli C: - unmyelinated - slow pain - dull, burning, aching, prolonged pain - more diffuse - elicited mainly by chemical stimuli or persisting mechanical/thermal stimuli
What are nociceptors?
Free nerve endings
What are descending inhibitory neurons?
Originate from the brain
Travel down spinal cord
Inhibits pain stimulus arriving at spinal cord
What are ascending spinothalamic tracts?
Transmits pain stimulus to thalamus in brain
Tracts project contralateral and ipsilateral
What are interneurons for in the pain pathway? How does it work?
Site of stimulus modulation
Non noxious stimulus downgrades the pain stimulus
Mediated by Aa/AB fibres (e.g. rubbing arm after knocking elbow)
What 3 abnormal pain states are there?
Peripheral sensitisation (abnormality of pain receptors or primary afferent neurons) Central sensitisation (abnormality of spinal cord - modulation problem) Altered perception in brain
What causes peripheral sensitisation?
Tissue inflammation in a chemical environment
- > chemical nociceptors continuously activated
- > changes to neuron
Why does central sensitisation happen? What does it result in?
Increased pain transmission via spinal cord
Results in animals responding in exaggerated matter to benign stimuli
What are NMDA receptors for?
= ‘gate keepers’ of spinal cord
Only open if glutamate binds and AMPA prod AP
If Mh dislodged from channel
Impact of sensitisation and plasticity?
Causes chronic pain
Outlasts original tissue injury or healing time
Pain lasting >3mo
E.g. dogs with OA or diabetic neuropathy
Fluid compartments?
60% of body is water
- 40%: ICF
- 20% ECF (15% ISF, 5% plasma)
What is the circulationg volume of dogs, cats, horses, rabbits, sheep and cows?
Dogs and horses: 8-9% BW (80-90ml/kg)
Cats, rabbits, sheep and cows: 6-7% BW (60-70ml/kg)
Which osmotic particles are found in the ECF, ICF and intravascular fluid?
ECF: Na+ and Cl-
Intravascular fluid: Na+, Cl- and colloidal proteins
ICF: K+ and proteins
Normal fluid maintenance requirements?
2-3ml/kg/day or 50-75ml/kg/day
Types of fluid loss? What is lost? From where? Effect on PCV and TP or osmotic potential? Examples of causes?
Whole blood: - e.g. haemorrhage - lose everything - intravascular space only - PCV and TP not altered in short term ECF: - e.g. diarrhoea, vomiting, diuresis - lose water, Na+ and Cl- - lost from ECF - osmotic potential of remaining ECF doesn't change, ICF not affected Protein rich ECF: - e.g. effusions, protein losing conditions, exudates - lose water, proteins, Na+ and Cl- - lost from ECF Pure water loss: - e.g. dehydration - lost from all 3 compartments - osmotic potentials all increased but same gradients so remaining water distributed in normal ratios
Aims of fluid therapy?
Replace like with like
Replace the volume lost
Replace the rate of loss
