Anaesthesia Flashcards
a) Phases of general anaesthesia (4)
b) Commonly used medication at each phase, and how administered
a) 1. Premedication, sedation
2. Induction
3. Maintenance
4. Recovery
b) Premedication: Acepromazine, α2 - agonists, opioids, benzodiazepines → tranquilisation / IV catheterisation
Induction: Propofol, alfaxalone → patent airways must be established
Maintenance: Isoflurane, sevoflurane → maintain patent airways, ventilatory support, monitor vitals
Recovery: α2 - agonists, opioids, NSAIDs → highest risk, vitals must be monitored until normalised
Main components of anaesthesia (4), where is affected with each component, and other features
- Unconsciousness: Reticular formation, Locus Caeruleus, frontal and prefrontal cortex → transient loss of memory
- Myorelaxation: Skeletal muscles, neuromuscular junction → loss of protective reflexes
- Immobility: Motor area of cerebral cortex → respiratory and cardiovascular depression
- Analgesia: Peripheral nociceptors, spinal cord, somatosensory cortex → impaired thermoregulation
Related risks of peri-anaesthetic complications (4)
- Species related
- Patient related
- Clinical status related (ASA-risk)
- Procedure related
Patient-related anaesthetic risks (3)
- Small/young animals - hypothermia
- Patient with liver dysfunction - bleeding, hypoglycaemic, delayed recovery
- Barchycephalic breeds - respiratory dysfunction / upper airway obstruction, high parasympathetic tone
ASA risk classification categories
ASA 1: normal healthy patient - minimal risk (eg castrate)
ASA 2: patient with mild systemic disease - slight risk (eg neonate, geriatric, controlled diabetic)
ASA 3: patient with obvious systemic disease - moderate risk (eg anaemic, liver disease, not well-controlled hyperthyroidism)
ASA 4: patient with severe systemic disease that is a constant threat to life - high risk (eg shock, uncontrolled diabetes, uncompensated heart disease)
ASA 5: patient not expected to survive without the operation - extreme risk (eg severe trauma, advanced heart disease)
ASA 6: patient declared brain dead, organs being used for donation
Premedication (sedation)
Overview of drug classes and licensing (5 types, 4 species types)
Premedication (sedation)
Phenothiazines: Acepromazine
a) Who is it suitable for
b) Pros (4) and cons (5)
a) Suitable for young healthy patients, risks in old geriatric patients
b) Pros: reliable in dogs, long-acting for smooth recovery, anti-arrhythmic properties, cheap and licensed
Cons: Unreliable in cats, long-lasting side effects, vasodilation causes hypotension, no analgesia, poor choice for aggressive animals
Premedication (sedation)
Phenothiazines: Acepromazine
mechanism of action
Premedication (sedation)
Butyrophenones (Azaperone)
Essential info
- Similar mechanism to acepromazine and can also produce hypotensive effects
- It is the only sedative licensed in pigs, and is only licensed for pigs
Premedication (sedation)
α2 agonists
a) Examples
b) Who suitable for/not suitable for
c) Pros and cons
a) Medetomidine, Dexmedetomidine (dogs and cats), Xylazine(dogs and cats, horses, cows), Romifidine (horses)
b) Suitable for young healthy patients, aggressive patients (IM) and non-conventional species. Not suitable for diabetic patients, >ASA 3 patients, cardiac disease patients
c) Pros: Good spinal analgesia, reliable in cats, dogs and equine, short acting, it’s an antagonisable sedative (Atipamezole an α2-antagonist can reverse effects)
Cons: Arrhythmogenic, hypertension/hypotension, cardiac and respiratory depression, moderately expensive
Premedication (sedation)
α2-agonists
a) Mechanism of action
b) Order of selectivity (α2 < α1)
b) Highest selectivity: Dexmedetomidine → Medetomidine → Romifidine → Detomidine → Xylazine :Lowest selectivity
(Dirty Minded Rabbits Don’t (need) X-rays)
Premedication (sedation)
Benzodiazepines
a) Examples
b) Who is it suitable for/not suitable for
c) Pros and Cons
a) Midazolam, Diazepam, Zolazepam
b) Suitable for seizure patients, fractious patients, old geriatric patients, cardiac disease patients, neonatal patients. Not suitable for young healthy patients, hepatic encephalopathy patients
c) Pros: Minimal cardio/respiratory effects, myorelaxation, can be used in neonates and geriatrics, anticonvulsant
Cons: Unreliable in small animals, behavioural excitability, antagonists are expensive, myorelaxation can lead to respiratory dysfunction
Premedication (sedation)
Opiods
a) Examples
b) Who suitable for
c) Pros and cons
d) What are they used synergistically with
a) Methadone, Buprenorphine, Fentanyl (cats and dogs), Butorphanol(cats and dogs, horses)
b) Suitable for invasive surgical patients, painful patients, cardiac disease patients. Risks in respiratory patients, asthmatic/allergic patients
c) Pros: Powerful analgesia, sedative effects, safe to use in cardiac patients, antagonisable sedative - NARCAN
d) Acepromazine, α2 agonists, benzodiazepines
Premedication (sedation)
Benzodiazepines mechanism of action
Premedication (sedation)
a) How do dosages change of acepromazine and α2 agonists when used in combination
b) Sedatives that must be administered IV
a) Decreased
b) Diazepam (benzodiazepine) and Fentanyl (opiod)
Premedication (sedative)
Opiod mechanism of action
Induction of anaesthesia
Stages of anaesthesia
Induction of anaesthesia
a) Steps of anaesthetic induction (6)
b) Advantages vs disadvantages of IV anaesthetic administration
a) 1. IM premedication 2. IV catheter placement 3. Pre-oxygenation 4. Anaesthetic agent administration 5. Endotracheal intubation 6. Connection to breathing system
Induction of anaesthesia
a) IV only drugs
b) IM and IV drugs
c) What is pre-oxygenation
a) Propofol, Ketamine, Thiopental
b) Zolazepam, Ketamine, Alfaxalone
c) 100% oxygen for 3 to 5 minutes
Induction of anaesthesia
Propofol mechanism of action + side effects
- Most common induction agent for dogs and cats
- Rapidly metabolised in liver and lungs (short duration)
- 2-6 mg/kg administered slowly, over 30-40s
Induction of anaesthesia
Alfaxalone mechanism of action + side effects
- Rapid hepatic metabolism
- 1-2 mg/kg IV over 45-60s
- Baroreceptor reflex better preserved than with propofol
Induction of anaesthesia
Ketamine mechanism of action + side effects
- More commonly used for large animals, used at sub-anaesthetic doses in dogs and cats as a complementary analgesic
- Poor myorelaxation, so often co-administered with benzodiazepines
Induction of anaesthesia
Etomidate mechanism of action + side effects
- Used particularly in animals with severe cardiovascular compromise as few effects on arterial blood pressure and cardiac rhythm
Induction of anaesthesia
a) Use of Tiletamine/zolazepam
b) Inhalation anaesthetics
a) Fixed 1:1 combination. Tiletamine produces similar analgesia to ketamine, zolazepam gives muscle relaxation.
IM dose: 10-20 mg/kg, 2-5 min onset
IV dose: 5-10 mg/kg, 30-60s onset
b) When IV access not possible, but this technique often causes distress to the animal.
Sevoflurane in oxygen is preferred as is less irritating on airways than isoflurane.
Breath holding is a problem
Maintenance of anaesthesia
Overview of the mechanism of action of inhalation anaesthetics
- Indcues a reduction in junctional conductance by decreasing gap junction channel opening times and increasing closing times
- Interaction with lipid-membranes
- GABA-A agonist
Maintenance of anaesthesia
a) What does the rate of anaesthesia recovery depend on (2)
b) What does the depth of anaesthesia depend on (1)
a)
- partial pressure changes in the brain, controlled by partial pressure changes in the alveoli
- partial pressure in the alveoli is determined by ventilation
b)
- partial pressure of anaesthetic in brain (determined by pp in alveoli)
Maintenance of anaesthesia
Side effects of inhalation anaesthesia causes
a) Cardiovascular depression (5)
b) Respiratory depression
c) Hepatotoxic
d) Malignant hyperthermia
a) 1. Negative inotropy (myocardial depression) 2. Peripheral vasodilation 3. Depression of tissue autoregulation 4. CNS depression (reduced sympathetic tone) 5. Halothane causes sensitisation of the myocardium to arrhythmogenic effects of catecholamine
b) Reduction in respiratory drive
c) Due to drug metabolism in the liver
d) Inherited gene mutation that affects muscles
Maintenance of anaesthetic
Nitrous oxide (N2O)
a) Characteristics (3)
b) Overview of mechanism of action
a) 1. Highly insoluble in blood -> rapid induction 2. Diffusion in gas filled spaces / cavity 3. No absorption with activation charcoal
b) Analgesia via NMDA receptors and opioid systems. Anaesthetic MAC > 100% therefore should be used in combination with other anaesthetics
Maintenance of anaesthesia
a) Define the minimum alveolar concentration (MAC)
b) What is the MAC dependent on
c) What to remeber in clinical settings
a) Concentration of vapour in alveoli of the lungs to prevent movement/motor response in 50% of subjects in response to surgical (pain) stimulation
b) Multiple biological parameters (species, age, health status)
c) End tidal concentration is close to alveolar concentration
Maintenance of anaesthesia
Important things to note for maintenance of anaesthesia using
a) Propofol (2)
b) Alfaxalone (3)
c) Ketamine (3)
a) 1. Slow metabolism in cats 2. Can have toxic effects
b) 1. Ventilatory support may be necessary 2. No accumulation 3. Tough recovery
c) 1. Cumulative build-up of drug 2. Active metabolite 3. Sub-anaesthetic doses used peri-operatively for analgesia
Maintenance of anaesthesia
Drug combinations in injectable anaesthesia
a) What do combinations involve
b) Triple-drip used in large animals
c) Triple-drip ised in cats
d) Quad protocol in kittens
a) 1. Sedative (eg α2-agonist) 2. Peripheral / central myorelaxant (eg benzodiazepines) 3. Anaesthetic agents or adjuvants (eg lidocaine, ketamine)
b) Midazolam, Xylazine, Ketamine
c) Butorphanol, Medetomidine, Ketamine
d) Midazolam, Medetomidine, Ketamine, Buprenorphine
Maintenance of anaesthesia
Partial intravenous anaesthesia
a) Describe what this is
b) Agents used (4)
c) Benefits (4)
a) Combination of inhalation anaesthesia and injection anaesthesia for maintenance of anaesthesia
b) 1. Fentanyl continuous rate infusion 2. Ketamine 3. Lidocaine 4. α2-agonist
c) 1. Superior quality of anaesthesia and analgesia 2. MAC-reduction 3. Addition of therapeutic effects 4. Reduction of side effects
Maintenance of anaesthesia
a) Describe the bolus technique
b) What is monitored to determine administration (5)
a) Administration of drug of choice at predetermined time intervals (eg every 10-15 minutes) based on duration of effects of the drug of choice
b) 1. Eye position 2. Eye reflexes 3. Movement 4. Physiological variables (heart rate, resp rate, arterial bp) 5. Muscular tone
Anaesthetic monitoring
Arterial Blood Pressure Monitoring
Complete the table
Anaesthetic monitoring
Methods of monitoring anaesthesia - advantages and disadvantages
Oscillometry
Advantages - 1. cheap and easy 2. Non-invasive 3. multiparametric modules
Disadvantages - 1. Arrhythmia decreases reliability 2. Not useful in rabbits 3. Intermittent measurement
Anaesthetic monitoring
Methods of monitoring anaesthesia - advantages and disadvantages
Doppler
Advantages - 1. real time measurement 2. useful in small animals 3. not affected by arrhythmia
Disadvantages - 1. flow sensor 2. reads MAP in cats, SAP in other species 3. electric interference
Anaesthetic monitoring
Methods of monitoring anaesthesia - advantages and disadvantages
Arterial line
Advantages - 1. gold standard technique 2. reliable in all species 3. measures arterial blood gases
Disadvantages - 1. invasive 2. expensive 3. risk of vasculitis, haemorrhage
Anaesthetic monitoring
Common causes of arrhythmia during general anaesthesia (5)
- Vagal stimulation (drug induced, intestinal/oesophageal/ocular manipulation)
- Hypothermia (bradyarrhythmia)
- Electrical currents applied close to the heart
- Mechanical stimulation of heart and vessels
- Hypoxaemia and hypercapnia
Anaesthetic monitoring
a) What is capnography
b) What to expect to show on a capnograph reading under the following conditions:
i) Rebreathing
ii) Upper airway obstruction
iii) Hypoventilation
iv) Hyperventilaton
v) Gas sampling issue
a) Rate of elimination of CO2 (produced by cellular metabolism) from the lungs ultimately indicates the efficiency of ventilation
b)
i) Elevated baseline
ii) Shark-fin curve
iii) Higher values
iv) Lower values
v) Abnormal plateau
Anaesthetic monitoring
Capnograph measurement methods
Complete the table
Anaesthetic monitoring
Pulse oximetry
a) What does it measure, and what is normal when breathing room air
b) Advantages
c) Disadvantages
a) O2 blood saturation - should be >97%
b) 1. Easy to use 2. Monitors both cardiovascular and respiratory function
c) Can be inaccurate in cases of 1. severe anaemia 2. pigmented mucous membranes 3. carbon monoxide poisoning
Anaesthetic monitoring
Spirometry
a) Clinical significance in monitoring anaesthesia
b) What does increased compliance mean and what can it signify
c) What does decreased compliance mean and what can it signify
a) Evaluation of lung volumes and pressures and their relationship
b) Low applied pressure generates high lung volume - seen in young, healthy patients (although higher than normal compliance can indicate COPD)
c) High applied pressure generates low lung volume - seen in elderly patients, or patients with respiratory disease (fibrosis eg)
Pain management
Pain Transmission
Complete the table
Pain management
Pain modulation pathways
a) Label the image
b) What are the excitatory neurotransmitters, and where do they act (3)
c) What are the inhibitory neurotransmitters, and where do they act (5)
b) 1. Glutamate (primary afferent) 2. Substance P (primary afferent) 3. Nerve growth factor
c) 1. GABA (primary afferent, inhibitory interneuron) 2. Glycine (inhibitory interneuron) 3. Serotonin (descending neuron, inhibitory interneuron) 4. Opiods (descending neuron, inhibitory interneuron) 5. Dopamine
Locoregional anaesthesia - small animal
General mechanism of action of local anaesthesia
- Na+ channel activation across the nerve axon allows propagation of the action potential
- Na+ flow out of the neuron axon to cause depolarisation of the membrane
- Local anaesthetics block the transmembrane Na+ channel - interfering with the propagation of the action potential
Locoregional anaesthesia - small animal
Overview of cranium nerve blocks
Complete the table
Locoregional anaesthesia - small animal
Infraorbital nerve block
a) Indications (2)
b) Procedure (3)
a) Upper jaw soft tissue desensitisation. Deep approach for tooth desensitisation (maxillary nerve block)
b) 1. Needle should be inserted into infraorbital canal opening 2. Needle should be parallel to canal or slightly ventral 3. Dorsal positioning of the needle can lead to rupture the globe of the eye
Locoregional anaesthesia - small animal
Maxillary nerve block
a) Indications (2)
b) Procedure (2)
a) Upper jaw teeth and soft tissue desensitisation. Tooth extractions
b) 1. Identical approach to the infraorbital nerve block (infraorbital canal) 2. Deeper penetration of the needle
Locoregional anaesthesia - small animal
Mandibular nerve block
a) Indications
b) Procedure
a) 1. Lower jaw teeth and soft tissue desensitisation 2. Tooth extractions
b) Direct needle towards mandibular foramen on the lingual side of the mandible, rostral to the angle of the mandible and caudal to the last molar in the middle 1/3 of the mandible
Locoregional anaesthesia - small animal
Mental nerve block
a) Indications
b) Procedure
a) Lower jaw soft tissue desensitisation
b) Direct needle towards mental foramen located ventral to the rostral root of the second premolars
Locoregional anaesthesia - small animal
Sciatic nerve block
a) Indications
b) Sciatic nerve anatomy (important function of branches)
c) Nerve stimulator guided
d) Ultrasound guided
a) Sensory and motor block to the pelvic limb, distal to the stifle joint
b) Tibial nerve branch provides flexion of stifle. Common peroneal nerve provides extension of stifle and tarsus
c) Insert subcutaneous insulated needle between the great trochanter of the femur and ischiatic tuberosity. Motor response elicited: 1. Plantar extension of caudal thigh muscles 2. Knee flexion/extension
d) Tibial nerve is a landmark of distal approach ultrasound
Locoregional anaesthesia - small animal
Femoral nerve block
a) Indications
b) Nerve-stimulator guided
c) Ultrasound guided
a) Sensory and motor block to the pelvic limb distal to the stifle joint
b) Insert needle cranial to femoral artery with tip orientated towards the bone. Motor response: 1. contraction of quadriceps femoris 2. Flexion/extension of the stifle
c) Identify within the femoral triangle - the artery, vein and nerve
Locoregional anaesthesia - small animal
Brachial Plexus (C6, C7, C8, T1) Block
a) Indications
b) Ultrasound guided
a) Sensory and motor block of thoracic limb distal to the elbow
b) Dorsal recumbency with linear probe positioned between sternum and scapula. Insert needle parallel to ultrasound beam
Locoregional anaesthesia - small animal
Epidurals (L7)
a) Procedure
b) Benefits over spinal nerve blocks (3)
a) Nedle inserted between ilium wings and processus spinosus of L7. Drop of saline inserted at needle hub when needle in skin/subcutaneous layer, needle then advanced until the drop is drawn into the body of the needle.
b) 1. Less invasive 2. Lower risk of iatrogenic damage to the spinal cord 3. Longer nerve block (although less intense)
Locoregional anaesthesia - large animal
Complete this summary table
Locoregional anaesthesia - large animals
Infraorbital nerve block
a) What used for (3)
b) Procedure
a) 1. Nares 2. Soft tissues of the naso-labial region 3. Periodontal tissues
b) Needle inserted into the infraorbital canal opening
Locoregional anaesthesia - large animals
Maxillary nerve block
a) What used for (2)
b) Procedure
a) 1. Soft tissues of maxillary 2. Teeth of upper jaw
b) Needle inserted beneath zygomatic arch
Locoregional anaesthesia - large animal
Mandibular nerve block
a) What used for (2)
b) Procedure
a) 1. Soft tissues of mandibular region 2. Teeth of lower jaw
b) Direct needle towards mandibular foramen on the lingual side of the mandible
Locoregional anaesthesia - large animal
Mental nerve block
a) What used for (2)
b) Procedure
a) 1. Soft tissues of rostral mandibular region 2. Periodontal tissues of the rostral mandibular region
b) Direct needle towards mental foramen
Locoregional anaesthesia - large animal
Corneal nerve block in goats
a) What used for
b) Anatomical landmarks (2)
a) De-horning
b) 1. Zygomatic arch and temporomandibular joint for the infratrochlear nerve (A in image) 2. Anterior aspect of the upper outer aspect of each orbit of the lacrimal nerve (B in image)
Locoregional anaesthesia - large animal
Corneal nerve block in cattle
Anatomical larndmarks for blocking
Corneal branch of the intratrochlear nerve found at the zygomatic arch
Ring of local anaesthetic around the horn
Locoregional anaesthesia - large animal
Inverted L Block (cattle)
a) What used for (3)
b) Procedure
a) 1. Rumenotomies 2. C-sections 3. Cystotomy
b) Inject at line delimited by paralumbar fossa (see image)
Locoregional anaesthesia - large animal
Paravertebral block
a) Anatomical landmarks
b) Procedure of proximal method
c) Procedure of distal method (Magda’s method)
a) Final rib (T13), transverse process of L1, L2, L3
b) Insert needle perpendicular to the transverse processes of L1, L2, L3. Before injecting, withdraw the needle, if plunger is sucked in, needle is too deep into peritoneum
c) Needle angled towards distal ends of lumbar transverse process of L1, L2 and L4
Locoregional anaesthesia - large animal
Limb nerve blocks
Intravenous regional anaesthesia procedure
- local anaesthetic injected in a peripheral vein of area of interest (only lidocaine or procaine can be used)
- Systemic absorption of local anesthetic is limited by torniquet
- Torniquet should be removed after 30 mins (risk of vascular/nerve damage)
- Not used in horses
