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)
Anaesthetic monitoring
Why can hypothermia occur in general anaesthesia (6)
- Decreased liver perfusion and metabolism
- Decreased cellular metabolism
- Myorelaxation
- Drug-induced impaired thermoregulation (eg opiods(
- Surgical preparation (clipping, disinfection)
- Opening of body cavities
Anaesthetic monitoring
a) Consequences of hypothermia during general anaesthesia (6)
b) Prevention of hypothermia during general anaesthesia (6)
a) 1. Increased morbidity 2. Increased infection rates 3. Impaired coagulation 4. Arrhythmia 5. Seizure 6. Pain
b) 1. Active warming devices 2. Heat and moisture exchanger filters 3. Blankets 4. Use of warm fluids for lavage of body cavities 5. Decrease fresh gas flow of breathing gases 6. Limit duration of anaesthesia
Anaesthetic monitoring
Assessing depth of anaesthesia - clinical signs
a) Too shallow
b) Surgical anaesthesia achieved
c) Too deep
d) Nociception assessment
a) Centrally positioned eye with normal pupillary and palpebral reflexs. Swallowing possibly observed
b) Ventrally-rotated eye with slow pupillary reflex and mild palpebral reflex
c) Mydriasis. Absent pupillary and palpebral reflexes
d) Deep pain may be assessed to evaluate opioid-induced analgesia, during surgery, but autonomic reflexes more commonly used
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
Pain management
Projection and perception of pain
a) Where are secondary neurons that project pain information
b) Where do these secondary neurons project information to (3)
c) Where does information get projected from these areas
a) Dorsal horn of spinal cord
b) 1. Thalamus 2. Limbic system 3. Reticular formation, hypothalamus and pons
c)
1. Thalamus → somatosensory cortex, frontal motor cortex
2. Limbic system → emotions
3. Reticular formation, hypothalamus, pons → autonomic responses, sympathetic NS, catecholamine release
Pain management
What are the 7 types of pain
- Acute pain
- Chronic pain
- Somatic pain
- Visceral pain
- Inflammatory pain
- Neuropathic pain
- Cancer pain
Pain management
Describe
a) Acute pain
b) Chronic pain
c) Somatic pain
d) Visceral pain
a) Trauma, surgical or infectious events, beginning abruptly. Resolves in days/weeks. Self-limiting serving biological purpose (adaptive, protective)
b) Persists beyond normal healing time. 1 to 3 months duration. Usually involves CNS changes
c) Superficial (pain associated with skin) or deep (associated with muscles, joints, tendons, bones). Well localised, arching, sharp and intense
d) Ischaemia, inflammation, stretching capsule, distension. Dull, diffused, poorly defined sensation. Associated with nausea, vomiting, change in ANS. Referred pain
Pain management
Describe
a) Inflammatory pain
b) Neuropathic pain (including peripheral and central sensitisation)
c) Cancer pain
a) Tissue injury, immune cell activation
b) Injury to nervous system causing increased activation of peripheral nociceptors and CNS activity
Peripheral sensitisation - change to nociceptors caused by tissue injury/inflammation causing a reduction in activation threshold and an amplified response to pain
Central sensitisation - increased efficacy in pain signal transmission even after nociceptors have stopped, due to a change in membrane excitability and decreased inhibition
c) Characteristic of both inflammatory and neuropathic pain
Pain management
What drug classes are used at the following stages of the pain pathway
a) Perception (5)
b) Modulation (5)
c) Transmission (4)
d) Transduction (4)
a) 1. Opioids 2. NSAIDs 3. Paracetamol 4. Gabapentinoids 5. NMDA antagonists
b) 1. Opioids 2. Tricyclic antidepressants 3. NMDA antagonists 4. Paracetamol 5. Cannabinoids
c) 1. Opioids 2. NMDA antagonists 3. Gabapentinoids 4. Cannabinoids
d) 1. NSAIDs 2. Corticosteroids 3. Piprants 4. Anti-NGF antibodies
Pain managements
Opiods
a) What stages of pain do they block
b) Analgesia mechanism
c) Clinical uses
d) Side effects (3)
a) All stages of pain proprioception
b) Reduce pre-synaptic NT release → hyperpolarise post-synaptic membrane → activates descending inhibitory pathways → inhibits ascending nociceptive input
c) Mild to severe pain (dependent on dose)
d) 1. Cardiovascular 2. Respiratory depression 3. GI dysfunction
Pain management
α2 agonists
a) What stages of pain do they block
b) Analgesia mechanism
c) Clinical uses
d) Side effects (6)
a) Block transmission, modulation and perception of pain
b) Decreased sympathetic discharge → modulation of nociceptive transmission → inhibit neurotransmitter release from nociceptors → alteration in transmission ascending nociceptive
c) Pain relief (routine procedures)
d) 1. Vasoconstriction 2. Bradycardia 3. Hypotension 4. Vomiting 5. Hyperglycaemia 6. Bronchoconstriction and oedema in ruminants
Pain management
NSAIDs
a) What stages of pain do they block
b) Analgesia mechanism
c) Clinical uses
d) Side effects (5)
a) Blocks transduction of pain
b) Inhibits COX-1 and COX-2 → reduced production of prostaglandins (except galliprant) → reduced production of tranexamic acid
c) Acute and chronic pain. Osteoarthritis in dogs. Multimodal protocol for pain management
d) 1. Vomiting 2. Diarrhoea 3. Polydipsia and polyurea 4. Increased appetite 5. Renal and hepatic injury
Pain management
Paracetamol
a) What stage of pain does it block
b) Analgesia mechanism
c) Clinical uses
d) Important notes
a) Blocks transduction, modulation and perception of pain
b) Inhibits COX-3 in the brain → prostaglandin inhibition → serotoninergic pathway activation → endocannabinoid enhancement
c) Classified as an NSAID so same uses
d) Do not use in cats as is very toxic. Dogs receive much lower doses than a human
Pain management
Ketamine
a) What stages of pain does it block
b) Analgesia mechanism
c) Clinical uses
d) Side effects (5)
a) Blocks transmission, modulation and perception of pain
b) NMDA antagonist → central sensitisation and anti-inflammation → descending pathway interactions with opioid receptors → local anaesthetic
c) Acute or chronic pain. Bolus or constant rate infusion
d) 1. Dysphoria 2. Muscle rigidity 3. SNS stimulation 4. Negative inotropic effect 5. Apneustic breathing
Pain management
Lidocaine / bupivacaine
a) What stages of pain does it block
b) Analgesia mechanism
c) Clinical uses of lidocaine
d) Side effects (IV) (5)
a) Blocks transduction, transmission and modulation of pain
b) Na+ channel blocker → gold standard to prevent pain transmission. Lidocaine (fast onset, short duration). Bupivacaine (slow onset, long duration)
c) Nerve blocks
d) 1. Nausea 2. Vomiting 3. CNS depression 4. Seizures 5. Cardiovascular depression, arrhythmia
Pain management
Gabapentin
a) What stages of pain does it block
b) Analgesia mechanism
c) Clinical uses
d) Side effects (2)
a) Blocks transmission and perception of pain
b) Blocks Ca2+ channels to reduce release of excitatory neurotransmitters → used in association with NSAIDs, opiods → sedative effects
c) Chronic neuropathic pain
d) 1. Diarrhoea 2. Constipation
Pain management
Amantadine
a) What stages of pain does it block
b) Analgesia mechanism
c) Clinical uses
d) Side effects (4)
a) Blocks transmission, modulation and perception of pain
b) NMDA antagonist → decreased central sensitisation → long onset of action
c) Acute or chronic pain
d) 1. Lethargy 2. Restlessness 3. GI upset 4. Seizures
Pain management
Monoclonal antibody treatment for osteoarthritis
a) Canines
b) Felines
a) Librella - bedinvetmab - targets nerve growth factor
b) Solensia - frunevetmab - targets nerve growth factor
Pain Management
Non-pharmacological pain treatment - how they work
a) Acupuncture
b) Laser therapy
c) Transcutaneous electrical nerve stimulation
d) Ice therapy
e) Heat therapy
a) Endorphin release. Wound healing. Immuno-modulation. Modulation of descending inhibitory pathways
b) Endorphin release. Vasodilation. Decreased inflammation. Faster wound healing and tissue repair
c) Endorphin release. Low voltage electric current. Treat acute pain and inflammation
d) Decrease in transmission of noxious stimuli. Decrease inflammation. Decreased tissue metabolism and O2 demand
e) Improve blood circulation to help tissue healing. Chronic pain relief
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
a) Local anaesthesia drug options (3)
b) Indications for local anaesthesia (3)
c) Most frequent dosing of local anaesthetics
a)
1. Lidocaine - quick onset, short duration
2. Bupivacaine and Levobupivacaine - Slower onset, longer duration (4 to 8 hours)
3. Tetracaine - Useful for topical anaesthesia, including using in opthalmology
b) 1. Improve perioperative pain management 2. Decreased opioid consumption 3. Patient welfare
c) 2 mg/kg
Locoregional anaesthetia - small animal
Neuraxial anaesthesia drug options (5)
- Local anaesthetics
- Opioids (morphine)
- α2 agonists (medetomidine, xylazine)
- Ketamine
- Steroids (treat chronic inflammatory pain)
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 - small animal
a) Advantages of peripheral nerve blocks (3)
b) Advantages of neuraxial blocks (3)
a) 1. Mono-lateral motor block 2. No cardiovascular side effects 3. No risk of spinal cord damage
b) 1. No risk of peripheral nerve damage 2. No risk of local anaesthetic toxicity 3. Doesn’t require expensive equipment
Locoregional anaesthesia - large animal
Complete this summary table
Locoregional anaesthesia - large animals
What must be considered with large animals when considering local anaesthetics
- In food animals, there are restricted drug use
- Only procaine is approved in food producing animals
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
Retrobulbar block
a) What used for
b) Procedure
a) Prodecured of the eyeball, including enucleation
b) Spinal needle placed through the skin perpendicular to the skull in the orbital fossa, caudal to the posterior aspect of the bony dorsal orbital rim. Eye will have a slight dorsal movement as needle passes through the fascia
Target nerves are axillary branch of trigeminal, occulomotor nerve, optic nerve block is a side effect (will cause transient blindness if eye isn’t removed)
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
Locoregional anaesthesia - large animal
Epidural nerve block
a) Anatomical landmarks for lumbar epidural vs coccygeal epidural
b) Procedure in horses and ruminants
a) Lumbar - processus spinous of last lumbar vertebra, ilium wings
Coccygeal - processus spinous of C1 and C2, sacro-coccygeal junction
b) Insert needle 45-90 degrees with respect to vertebral column. Remove stylet and apply a drop of saline at the needle hub. Slowly forward needle through subcut and muscular layer. ‘POP’ = ligamentum flavum crossed. Draw back, inject for 30-60s
Rabbits
Normal physiological parameters
a) Heart rate
b) Respiratory rate
c) Systolic arterial pressure
d) Temperature
e) Total blood volume
a) 180-240 bpm
b) 50-60 bpm
c) 90-120 mmHg
d) 37.7-38.8 C
e) 50-60 ml/kg
Rabbits
Anatomical considerations
a) Soft tissues of mastication (3)
b) Dentition (2)
c) GI
a)
- Well-developed masticatory muscles
- Limited opening of the mandibular joint
- Pulling tongue during intubation may cause vagal reflex
b)
- Continually growing teeth
- Dental disease often causes anorexia
c)
- Cannot vomit due to well-developed cardia and epiglottis
- No peri-operative fasting as can cause hypoglycaemia and stress
Rabbits
Anatomical considerations
a) Cardiovascular baroreceptors (4)
b) Metabolism (6)
a)
- Hypotension may stimulate both sympathetic and parasympathetic systems
- Rabbits lack a compensatory tachycardic phase during hypotensive shock
- Very sensitive to (inappropriate) handling-related catecholaminerelated stress
- Peri-anaesthetic ventricular tachyarrhythmias are common and can be fatal
b)
- Rapid basal metabolic rate, especially in small rabbits
- Prone to hypothermia during anaesthesia
- Ears are used as a means of thermoregulation
- Quicker drug metabolism and elimination than in other mammals
- Endogenous production of high levels of atropinesterases, so atropine has reduced efficacy in rabbits
- Glycopyrrolate should be used instead to reduce GI side effects of atropine at high doses
Rabbits
IV catheterisation sites (3)
- Lateral vein in ear (auricular)
- Cephalic vein
- Saphenous vein
Topical use of local anaesthetic
Rabbits
IM induction of anaesthesia in rabbits
a) Protocol drugs in healthy rabbits (3)
b) Protocol drugs in unhealthy rabbits (3)
c) Triple shot protocols (2)
a) Medetomidine, buprenorphine, ketamine
b) Midazolam, buprenorphine, alfaxalone
c) (all antagonisable) 1. Medetomidine, midazolam, fentanyl 2. atipamezole, flumazenil, naloxone
Rabbits
Intubation procedure
a) Procedures not recommended vs recommended
b) Angle of intubation
c) Preventative measures of laryngeal spasm
d) What can occur when pulling the tongue
e) V-gel
a) Blind intubation not recommended (high risk of laryngeal injury). Endoscope guidance or or oesophageal stethoscope-guidance recommended
b) 110 degree angle between base of the tongue and tracheal inlet
c) Topical lidocaine applied
d) Can cause vagal reflex
e) Specifically designed for rabbits. Occludes oesophagus rather than entering trachea. Atraumatic. But expensive, and can only use 40 times
Rabbits
a) Drugs for maintaining anaesthesia in rabbits
b) Systemic analgesics - Which can be used SC, IM and IV
c) Systemic analgesics - which can be used IV (continuous)
d) Systemic analgesics - which can be used SC and PO
e) Systemic analgesics - which can cause GI hypomotility/stasis
a) 1. ‘Top-up’ ketamine 2. Isoflurane/sevoflurane
b) Butotphanol, Burenorphine, Carpofen
c) Fentanyl
d) Meloxicam
e) Butorphanol, Fentanyl, Buprenorphine
Rabbits
Anaesthetic monitoring techniques (6)
Oscillometry
- Thoracic limb positioning
- Unreliable during hypotension
Doppler
- Measure SAP and monitor peripheral pulse
Arterial Line
- Auricular artery
- Easier in big rabbits
Pulse Oximetry
- Neonatal device required to read frequencies above 200bpm
Electrocardiography
- High frequency, low voltage signal
- Low filters
- 100-200mm/sec
Capnography
- Side stream samples 70 – 150 mL/min (more than rabbit tidal volume)
- Microstream (laser) samples 50mL/min but expensive
- Main stream undesirable due to dead space
Farm animal anesthesia
Physiological considerations of ruminants (5)
- They eat frequently throughout the day, meaning prolongued fasting can lower blood electrolytes, cause hypoglycaemia and acid-base imbalances
- Metabolic acidosis from fasting, dehydration, hypersalivation
- Metabolic alkalosis from hypochrolaemia
- Prone to regurgitation and ruminal tympany (impaired respiratory mechanisms)
- Prey animals so pain assessment challenging (don’t show signs)
Farm animal anaesthesia
a) Preparation for anaesthesia in ruminants
b) Where is the vascular access in pigs
a)
- Catheter placed in jugular vein
- Preoperative IV fluids to prevent dehydration
- Fasting
- Mouthwash before endotracheal intubation
b)
- Auricular, lateral saphenous or cephalic vein
- jugular only for experimental procedures
Ruminant anaesthesia
Fasting before anaesthesia
a) Calves, sheep, goats
b) Adult cattle
c) Pigs
a) 12-18 hours (8-12 hours no water)
b) 24-36 hours
c) 12 hours
Farm animal anaesthesia
Licensed drugs for food producing animals
a) Cattle (5)
b) Pigs (5)
a)
- Ketamine
- Detomidine
- Xylazine
- some NSAIDs
- Procaine
b)
- Azaperone
- Xylazine
- Ketamine
- some NSAIDs
- Procaine
Farm animal anesthesia
Anaesthetic considerations
a) α-2 agonists in ruminants
b) Goats and xylazine
c) Pigs and xylazine
d) What drugs to use epidurally
a) Can produce hypoxaemia in healthy ruminants, serious complications in animals with pre-existing hypoxaemia
b) More sensitive to xylazine than other species
c) Not very effective, but still have side effects
d) Xylazine, ketamine, procaine
Farm anaesthesia
a) Positioning of farm animals during anaestheisa
b) Preventing bloating
a)
- Padding to prevent compartmental crush syndromes
- Nares above heart level to prevent nasal oedema
b)
- Stomach tube
Farm animal anaesthesia
Complications in calves
- if presented for abdominal surgery, often dehydrated so need fluid therapy
- prolongued starving causes metabolic acidosis and hypokalaemia
- possible compensatory respiratory alkalosis
Farm animal anaesthesia
Complications of dorsal recumbency
- dorsal recumbency and bloat can cause cardiorespiratory impairment
- decreased venous return and hypotension
- impairment of respiratory mechanics, hypercapnia and hypoxaemia
Farm animal anaestheisa
Malignant hyperthermia in pigs
- hereditary disorder of skeletal muscle homeostasis causing uncontrolled calcium release from sarcoplasmic reticulum
- can occur during inhalation anaesthesia
- causing hyperthermia, hypercapnia, ventricular arrhythmias, death
Farm animal anaesthesia
Early signs of anaesthetic recovery (4)
- nystagmus
- swallowing
- increased musclular tone
- movements
