VNSA11 Flashcards
What does general anaesthesia provide?
Muscle relaxation
Analgesia
Unconsciousness
Define general anaesthesia
The reversible immobile state that induces amnesia
Name anaesthetic types
General anaesthetic
IV induction agents
Inhalation gases
Epidural
Local anaesthetic
Dissociative
Topical
Regional
Local anaesthesia
Used alongside GA
Temporarily blocks conduction in sensory nerve fibres preventing nociceptibe info to be received.
Mode of action - inhibits sodium channels in neuronal membranes, preventing influx of sodium ions into nerve axons.
Nervous function lost in order: pain, cold & warmth sensation, touch, deep pressure, motor function
Pharmacokinetics of local anaesthetics
Absorption: depends on dose, site on inj and if there’s a presence of a vasoconstrictor
Distribution: affected by degree of protein binding. Free drug exerts effects and is metabolised. Metabolism via liver and lungs, excreted via kidneys.
Local anaesthetic can cause vasodilation (often used with adrenaline to delay absorption and lengthen action). Vasoconstrictors can cause localised ischaemia so not used in distal areas as potential necrosis.
Effects: lipid soluble and low molecular weight (cross blood-brain barrier). At therapeutic range these are of great use (anticonvulsants, sedatives and analgesia) at high levels can induce seizures and cause CNS depression. Can slow myocardium conduction causing vasodilation, hypotension, bradycardia and cardiac arrest. Cats and exotics are more susceptible to this than dogs
Local anaesthetic drugs
Lidocaine: rapid onset of activity, good tissue penetration. Short duration of activity (45 mins without adrenaline & 1-2hrs with). Good for regional blocks and general surgery.
Proxymetacaine: topical analgesia of eye, rapid onset but duration only 15 mins. Causes less initial sting than other agents.
Bupivacaine: slow onset of activity (15 mins) but longer duration (6-8 hrs). Potency 4X stronger than lidocaine. Good for epidural analgesia and post-op. Don’t give IV as cardiac toxicity risk.
What is topical anaesthesia (local)
Eg sprays, drops, gel or cream
Limited to analgesia of nasal mucous membranes, eye, larynx, penis, vagina, rectum and urethra.
Perineural (regional) block
(Local anaesthetic)
Injected directly around the nerve, reduces motor side effects and risks of systemic absorption and subsequent toxicity.
Nerves must be palpable and easily accessible - use of nerve stimulators and ultrasounds
Eg:
Intercostal nerve block: injected caudal to ribs
Brachial plexus block: analgesia distal to elbow
Maxillary and mandibular nerve blocks: dental and jaw surgery, nerves blocked as exit jaw bones
Intra-articular block (local anaesthetic)
Local anaesthetics or opioids injected into the joint cavity following surgery or arthroscopy.
Used as part as multimodal analgesia
Asepsis to prevent introduction of infection into the joint.
Epidural (local anaesthetic)
Performed by vs only
22G needle, or a 17G/18G tuohy needle
Inserted 90 degrees into skin surface and advanced slowly, stylet removed as it nears epidural space.
Eg; lumbosacral epidural, analgesia to structures caudal to thoracolumbar junction.
Bupivacaine used as long duration of action. Preservative free morphine can be used for analgesia of 18-24hrs
Local infiltration block (local anaesthetic)
Intradermal or subdermal tissue infiltrated by injection of local anaesthetic agent.
Uses: minor procedures used with sedation and or restraint.
Sterile needle injected into area. Draw back on hub to ensure no accidental vascular access. Inject small amount of local, creating a wheel effect.
If each injection is made at the periphery of the previous site the patient will only feel 1 injection.
Adrenaline may be used to delay local absorption and lengthen duration of action
Intravenous regional anaesthetic (Bier block)
(Local anaesthetic)
For surgical procedures in the body’s extremities, eg; toe removal.
Local is injected IV into area below or between two tourniquets (Esmarch bandage) on a limb.
Rapid onset of local in this area
Dissociative anaesthesia
KETAMINE
Has minimal effect on the respiratory system whilst creating analgesia and amnesia.
Patient presents as not anaesthetised as can swallow and eyes remain open.
Used in brief, superficial procedures or diagnostic processes.
Can be used in trauma patients (low bp) or elderly patients.
Recovery symptoms of dissociative anaesthesia
On recovery patient may present with;
Hypersalivation
Hyperventilation
Tachycardia
Muscle twitches
Paddling of the legs
Curling of the tongue
Physiology of anaesthesia
Produces many effects on the autonomic nervous system
Effects the brain by the anaesthetic agents acting on the receptors in the CNS and cell membrane of neuronal cells.
Anaesthetic agents cause a reversible depression on the CNS function resulting in loss of consciousness.
Blood-brain barrier: this barrier restricts movement of molecules into brain (water, oxygen and carbon dioxide can cross easily others cross more slowly to not at all). This depends on particles molecular size and lipid solubility.
HIGH lipid solubility and SMALL molecular weight crosses EASILY
The EASIER they cross the barrier the MORE potent they are as anaesthetics.
General anaesthesia; effects on the cardiovascular system
Often causes cardiovascular depression due to
Drugs depressant effect on the brain & peripheral effects of the drug.
Reduction in cardiac output — reduction in blood flow around the body — potential for tissue hypoxia
General anaesthesia; effects on the resp system
CNS depression causes a central depression of resp system.
Leads to reduced sensitivity to blood carbon dioxide concentration and reduced resp drive
Hypercapnia = higher blood CO2 than normal
Hypoxia = inadequate O2 delivered to tissues.
General anaesthesia; effects on the liver
Blood reaches the liver via the hepatic artery and portal vein.
Inhalant anaesthetic agents reduce liver blood flow to a degree due to reduction in cardiac output which affects relationship between hepatic artery and portal vein.
General anaesthesia; effects on the kidneys
Kidneys receive ~20% cardiac output
Normal renal function is reliant on adequate renal blood flow
By reducing that blood flow, GA also decreases glomerular filtration rate, urine output and electrolyte function.
Parameters should return to norm ranges within a few hours of a short GA.
Define MAC
Minimum alveolar concentration
What is the minimum alveolar concentration (MAC)
Amount required to suppress movement to noxious stimulant in 50% of patients.
About MAC
A measure of anaesthetic potency
Potent inhalant agents have a lower MAC.
Dependent on: species, age, temp, disease, CNS depressant drugs, pregnancy
Drug MAC levels
Halothane 0.75%
Isoflurane 1.15%
Sevoflurane 2.05%
Desflurane 5-10%
Halothane = most potent
Halothane
BG 2-3 and MAC 0.75%
High solubility coefficient
Absorbed quickly into the blood, but doesn’t want to come out
Concentration in the brain rises slowly as the blood reaches the brain (slow induction results)
At the end there is an accumulation of drug in the blood and fat and other tissues
Levels fall slowly as agent is slowly released into alveoli and exhaled
Slow recovery results
Isoflurane and sevoflurane
Low solubility coefficient
Slower absorption into blood, but released readily into brain
Rapid induction of anaesthesia
Agents are eliminated quickly by lungs
Rapid recovery
Drug blood-gas solubility
Halothane 2-3
Isoflurane 1.4
Sevoflurane 0.6
Desflurane 0.42
Halothane has a slow induction and Desflurane has quickest recovery
Soluble anaesthetic agents
Slow induction, slow recovery
Insoluble anaesthetic agent
Rapid induction, rapid recovery
Define critical tension
The necessary drug concentration needed in the brain to induce unconsciousness.
(As levels fall below critical tension the animal will regain consciousness)
Define pain
A sensory or emotional experience associated with actual or potential tissue damage
Analgesia
A conscious sensation
An adequately anaesthetised patient will not experience pain
A noxious stimulus is damaging to tissues (thermal, mechanical and chemical)
Nociception causes perception of pain (experienced during recovery)
Activation of pain pathways may cause surrounding tissues to become painful. Sensitivity to pain heightens due to repeated activation of nociceptive pathways
What 3 categories is pain split into?
Physiological
Inflammatory
Neuropathic
Physiological pain
Early warning device of potentially painful stimuli
Pain is proportional to stimulation
Pain experienced is localised
“Normal” pain pathway activation
Inflammatory pain
Pain associated with changes to pain pathway
-heightened pain sensitivity
-skin incision causes inflammation and tissue damage
Control of disease process causing pain hypersensitivity
Neuropathic pain
Clinical pain caused by nervous system damage
-peripheral nerve damage
-“phantom limb” pain following amputation
Clinical pain is associated with hypersensitivity (at site of tissue damage)
Stimuli that wouldn’t normally activate pain pathways will cause other pain
Stimuli normally activating pain pathways will cause a prolonged and larger pain (hyperalgesia)
Peripheral sensitisation
Noxious stimuli at site of tissue injury produces a more intense and prolonged pain response following clinical pain (primary hyperalgesia)
Nociceptors at site of tissue injury becomes more excitable
Central sensitisation
Resulting in secondary hyperalgesia, allodynia and spontaneous pain
Starts where peripheral nerve reaches spinal cord
Causes sudden augmentation of noxious stimuli as transmitted to brain
Pre-emptive analgesia
Analgesia provided before noxious stimuli
Prevents “sensitisation” or “wind-up”
Analgesia that has taken place after this is less effective
Multimodal analgesia
Using multiple analgesic drugs
Controlling pain at different levels and sites
Synergism between drugs means lower levels of each is needed reducing side effects
Adequate analgesia speeds recovery
Physiological effects of pain
Tachycardia
Inc blood pressure
Tachypnoea
Changes in resp pattern
Panting
Pyrexia
Salivation
Pupillary dilation
Shivering and shaking
Assess patients behaviour and demeanour without interference = more accurate
Response to pain
(Spinal, medullary, hypothalamic, cortical)
Spinal - receives the pain message transmitted from nociceptors which is then sent to the brain
Medullary - once in the brain the pain message is processed and responded to
Hypothalamic - releasing hormones which travel in the portal blood to the pituitary gland where ACTH is produced and released into the general blood system.
Cortical - adrenal cortex release corticosteroids under the influence.
Routes for administration of analgesia
IV - rapid action, potent opioids
IM - volume to inject and site considered. Painful.
S/C - onset of action is slower than IV or IM.
Transmucosal - as effective as IV administration of buprenorphine in cats. Some formulations are unpalatable
Transdermal - “patches” used to provide long term non-invasive analgesia. Reservoir of drug, covered with membrane controlling absorption rate. Bioavailability varies (cats 34% and dogs 64%).
Analgesia in rabbits and rodents
Opioids - good analgesia (Buprenorphine), wide safety margin but causes a degree of sedation, can be administered orally, causes pica in rats.
NSAIDs are very effective but higher doses required
Ketamine and alpha-2 agonists used as part of anaesthetic protocols
Analgesia in birds
Opioids used (kappa opioids receptors more effective than uu)
Response between species varies
NSAIDs used - nephrotoxicity and gastric ulceration seen. Repeated doses are unadvisable.
Define tidal volume
The amount of air that moves in or out of the lungs with each respiratory cycle
Define minute volume
Amount of gas inhaled or exhaled from the lungs in 1 minute
Expiratory reserve volume (ERV)
Amount of air you can forcefully exhale past a normal tidal expiration
Inspiratory reserve volume (IRV)
Amount of air that can be taken into the lungs (above the tidal volume) upon forceful inspiration
Define residual volume
The volume of air remaining in the lungs after maximum forceful expiration
Define vital capacity
Maximum amount of air a person can expel from the lungs after a maximum inhalation
(ERV + IRV + tidal volume)
Define total lung capacity
The amount of air the lung can contain at the height of maximum inspiratory effort
(Residual volume + vital capacity)
Define functional residual capacity (FRC)
The volume in the lungs at the end expiratory position
(ERV + residual volume)
Define physiological (anatomical) dead space
Volume of air in the respiratory zone that doesn’t take part in gas exchange
(Tranches down to the terminal bronchioles)
Define equipment dead space
Dead space resulting from devices placed between the ET tube and the y-piece of the breathing circuit
Define compliance
Measurement of pressure in a breathing system.
Affects the tidal volume of gas the patient receives.
Increases in compliance can decrease tidal volumes.
What is the difference between a sedative and a tranquilliser?
Sedative - promotes calm and induces sleep
Tranquilliser - reduces tension or anxiety but does not induce sleep
What is a narcotic?
Drug that in moderate doses dulls the senses, relieves pain and induces sleep but in excessive doses causes stupor, coma or convulsions
Define neuroleptanalgesia
Joint administration of a tranquilliser and an analgesic
Relief of surgical pain
What is the anaesthetic sparing effect?
Some medical agents have the ability to reduce the need for the full anaesthetic agent dose.
(Premeds and N20)
What is the second gas effect?
N2O is very insoluble in the blood but rapid absorption from the alveolus increases the speed of anaesthesia induction. The same happens when N2O is stopped, speeds up the removal of volatile agent
Patient should be fed 100% oxygen for 5-10mins after nitrous oxide has been turned off
Must be carefully scavenged
What is diffusion hypoxia?
When N2O is stopped it moves to alveolus in high concentrations diluting the alveolar air and therefore the amount of oxygen, if an animal breaths room air it can cause diffusion hypoxia.
To avoid this the patient should have 100% oxygen for about 5-10mins after N2O is stopped.
What is the triad of balanced anaesthesia
-loss of consciousness
-muscle relaxation
-analgesia
What is so important about pre-medication
-calms the patient before induction
-reduces amount of anaesthetic needed for induction and maintenance
-contributes to the triad of anaesthesia
-analgesia
-smoother recovery
Neuroleptanalgesia
Most premeds are a combination of drugs (sedative and opiate analgesic)
Benzodiazepine and opiate
Phenothiazine and opiate
Alpha-2 and opiate.
Synergistic effect inc quality and depth of sedation
Lower dose rates
Minimises side effects
In high doses there is sufficient CNS depression for minor surgical procedures
Dissociate anaesthetics
KETAMINE
These drugs induce CNS depression characterised by feeling dissociated from surroundings
Unconsciousness and analgesia but little muscle relaxation
Animals keep their eyes open - consider eye protection
Complicating monitoring
Define TIVA
‘’Total intravenous anaesthesia’’
No specialised equipment necessary
Drugs can be given IV or IM
Induction is rapid and stress free
Little technique or experience needed
No pollution hazard
Once administered dose cant be altered - hard to regulate depth
Drugs must be metabolised before recovery
May experience peaks and troughs in plane of anaesthesia if not using CRI
Define PIVA
‘’Partial intravenous anaesthesia’’
Syringe driver often needed
Both IV and inhalation agents used to maintain an adequate plane of anaesthesia
Patients intubated
Airway is protected and O2 administered
Depth of anaesthesia can be monitored and controlled
Recovery doesn’t rely on metabolism of the drug
Good for small furries when a rapid recovery is desired
Requires an anaesthetic machine and oxygen supply
Staff training
Provides control of anaesthetic vapour
Potential pollution of environment - scavenging needed
Damage to ozone layer
Define potency
Alveolar concentration of inhalation anaesthetic that prevents movement in 50% of animals in response to a noxious stimulus
Define volatility
Liquid at room temp but evaporate easily for administration by inhalation
(Nitrous)
Define solubility in tissues
Measure of how an agent is taken into tissues or organs
Define flammability
A measure of how quickly a specific material is capable of catching fire and burning
Define chemical stability
The materials ability to withstand change from chemical contact
Drugs ability to remain in the same chemical form when exposed to various environmental conditions.
Depth of anaesthesia
Depth depends on concentration in the brain.
Most inhalant agents cross the blood brain barrier with ease as they’re lipid soluble.
Process of anaesthesia (anatomy)
- Inhaled into lungs
- Cross the alveolar membrane and pulmonary capillary endothelium
- Dissolve in the blood and taken via pulmonary circulation to the left hand side of the heart and all body tissues
- Cross blood-brain barrier
- Exert their effect (unconsciousness)
Ideal properties of inhalation agents
-easily vaporised
-low blood/gas solubility
-MAC sufficiently low so that a high concentration of oxygen can be delivered
-Non-irritant to mucus membranes
-Good analgesic
-little depression/effect on respiratory or cardiovascular system
-good muscle relaxation
-minimal or no metabolism
-non-toxic to tissues
-non-flammable and non-explosive
-stable for storage
-compatible with soda lime
Oxygen (carrier gas)
Essential for supporting life
Administered at concentrations between 33-100%
Explosive combination with flammable agents
Nitrous oxide (Carrier gas)
Weak anaesthetic agent
Very good analgesic properties
Lower concentration of inhalant agent needed - balanced triad of anaesthesia
Minimal effect on cardiovascular and respiratory system
Not to be used at concentrations greater than 70% of the inspired gas mixture
Minimum 30% oxygen to prevent hypoxia
Not removed by soda lime and not suitable for circle or “to and fro” circuits
Neuromuscular blocking agents (NMBA) what does it provide
Adequate muscle relaxation essential for surgery
Cessation of movement
Reduced amount of inhalant agent needed (reduces cardiovascular and respiratory side effects also)
Without it causes increased tissue traction during surgery and pain and inflammation post op
How can muscle relaxation be provided ?
GA - marked muscle relaxation, but still potential of sudden movement
Local anaesthetic - around a peripheral nerve - blocking conduction of nerve impulse
Local anaesthetic into intrathecal or epidural space.
NMBA
What caution is needed when using NMBAs
Careful monitoring (use peripheral nerve stimulation electrodes when redosing)
Checking the plane of anaesthesia regular - may become light but cant respond
Supportive ventilation with IPPV
Superficial nerves used to check NMBA
Ensure ventilation is normal before recovery
Depolarising agents VS non-depolarising agents
Depolarising - suxamethonium. Bind reversibly to ACh receptor and open channels. Not often used in veterinary. Muscle pain on recovery.
Non-depolarising - Bind reversibly to ACh receptors but do not open channels. Ach cant bind so muscle doesn’t contract. Used in practice.
Vecuronium: duration of action = 30 mins in dog and cat, non-cumulative, may induce tachycardia, replaced by atracurium.
Atracurium: duration of action 30-40mins in dogs and cat. Breaks down spontaneously in body - used in patients with poor hepatic or renal function. Inactivated by alkaline solutions. Flush catheter before administering.
What are the 4 stages to anaesthesia?
Stage 1: voluntary excitement - induction to unconsciousness. Fear, stress, apprehension, disorientation, prominent muscle activity, may U and D, resp and heart rate.
Stage 2: involuntary excitement - unconsciousness to unexcited and stable respiration. Howling, excessive movement/struggling, reflexes still present, eyes open and central but eyes dilated, respiration irregular then stable.
Stage 3 plane 1 (light) - heart rate + pulse slightly reduced and regular, smooth regular resp pattern, head and limb movement absent other reflexes present but less, nystagmus can be seen, muscle tone present and responsive.
Stage 3 plane 2 (medium) - heart rate regular but reduced, pulse strong and regular, decrease in tidal volume, muscle tone relaxed, palpebral reflex slow or absent. Pedal reflex slow then absent, corneal reflex present, no nystagmus.
Stage 3 plane 3 (deep) - heart rate and blood pressure reduced further, pulses weak, decrease in tidal volume, only corneal reflex present, eye centrally fixed, 3rd eyelid in correct position, muscle tone greatly reduced or absent.
Stage 4 (overdose) - ending with resp muscle paralysis, great reduced and irregular resp rate progressing to apnoea, reduced heart rate, CRT, pulses weak and slow, reflexes absent inc corneal, eyes central and fixed, pupils dilated and unresponsive to light, flaccid muscle tone
What is the pin index system?
On the anaesthetic machine
Pin holes on cylinder and yoke
Pins are placed in different positions for different gases to prevent them being attached to the wrong outlet
What is a schrader probe?
Used to connect to pipeline outlet
Designed so will only connect with correct pipeline gas outlets.
All the hoses have the same male bayonet fitting but each gas supply has a protruding indexing collar with unique diameter
What is a Boyle’s bottle?
Uncalibrated vaporiser
“Draw over types”
Vaporiser output cannot be predicted so rarely used
Gas drawn over vaporiser by patients resp effort
So higher the patients minute volume the more gas passes through the vaporiser so the higher the concentration of inhalation agent
Calibrated vaporiser
“TEC’ / Penlon” types
Produce known anaesthetic vapour concentration regardless of temp and fresh gas flow rate
Serviced annually
Anaesthetic agent specific
Vaporisers
Modern day = temperature, level and flow compensated
Temp = constructed of metal which acts as a reservoir and conductor for heat energy, thermostatic valve in the bypass chamber - changes the flow depending on the temp in chamber.
Level = fibrous wicks so the agent climbs by capillary action, this increases the surface area for vaporisation, change in liquid level has no effect on vaporiser output.
Flow = the path of the gas through the vaporiser means it remains close to the wicks for a longer period of time. Reduces effect of high gas flows through the vaporiser. Supported by a back bar. Locked Into position.
Name the low oxygen warning devices
Ritchie whistle = uses oxygen in the cylinder to sound alarm, sounds when oxygen supply is first connected.
Howison oxygen failure alarm = sounds alarm and cuts off other gas supplies
Bosun whistle = unreliable as whistle relies on nitrous oxide flow, risks due to environmental contamination
What is a oxygen-nitrous oxide proportioning device
Anaesthetic machines will not supply nitrous oxide without oxygen.
Preventing supply of hypoxic mixture to patient
What is active scavenging
Preferred technique
Uses extractor fans to create negative pressure
Pressure break incorporated to prevent excessive negative pressure on patient (Barnsley receiver)
What is passive scavenging ?
Gases moved by the patients resp effort into activated charcoal system (gravity fed)
Scavenging tube no longer than 1.5m and not kinked
Canister weighed regularly (max weight 1.40kg)
Doesn’t absorb nitrous
What is active-passive scavenging
Tubing is used as with the passive system but connected to a forced ventilation system. Gases must not be re-circulated to another area of the building
What is the full weight of an oxygen cylinder
137 bar
What is the weight of a nitrous oxide cylinder ?
44 bar
What are the 3 main functions of an anaesthetic machine?
To deliver oxygen rich carrier gas and anaesthetic vapour to the patient
Carry carbon dioxide rich gas away from the patient
Deliver potentially harmful waste anaesthetic gas to the scavenging system
Define resistance
The ability of the patient to be able to breathe through the circuit. Resistance can be caused by the valve, canisters and tube length.
Lighter patients are more likely to encounter resistance
Define mechanical dead space
Too much equipment between the patient and the anaesthetic machine.
Define circuit drag
The part of the circuit that harbours gaseous space that is respired at every breath but doesn’t participate in gas exchange.
Eg - heavy tubing, valves, canisters as this can lead to disconnection or extubation.
What is an open anaesthetic circuit?
Lint or gauze placed on the nose of the animal and volatile anaesthetic agent dropped onto the material.
What is a semi-open anaesthetic circuit?
Same as open but gauze is placed inside a mask and attached to oxygen
What is a semi-closed circuit?
The use of an anaesthetic circuit to deliver the agent, but doesn’t involve soda lime and is referred to as a non-re-breathing circuit.
The gas flow has to be high enough to flush old gases out of circuit.
What is a closed circuit?
Same as a semi-closed circuit but soda lime is used to absorb carbon dioxide so the patient can re-breathe the same gas.
Semi-closed (non-rebreathing) circuits
Mapleson classification: categorised by appearance
Deliver oxygen and anaesthetic agents and eliminate carbon dioxide
Components- fresh gas flow, reservoir bag, breathing tubes, expiratory valve and patient connection.
5 basic types A-F but only A, D, E, F are used today.
What circuits are Mapleson A?
Magill and lack
What circuits are Mapleson D?
Modified Bain
Modified Ayers T-piece
(Has a bag and APL valve)
What types of circuits are Mapleson E?
Ayres-T
(No bag and no APL)
What type of circuits are Mapleson F?
Modified Ayres-T (Jackson Rees modification)
(Has a bag with a hole in it and no APL)
What are the indicators for soda lime?
Pink soda lime turns white when exhausted
White soda lime turns purple when exhausted
Advantages and disadvantages of red rubber ET tubes
A - reuseable, wide range of sizes, autoclavable, pre moulded so easy to intubate
D - expensive, perish with time, kink easily, can be irritant to the airway, unable to see contamination unless looking down, low volume and high pressure
Advantages and disadvantages of PVC ET tubes
A - cheap, can be reused, malleable when warm, fairly kink resistant, non-irritant, easy to place, easy to see contamination, high pressure and low volume available.
D - designed to be disposable, limited sizes, cannot be autoclaved, connections can become loose once PVC becomes warm.
Advantages and disadvantages of silicone ET tubes
A - same as PVC but can be repaired and autoclaved
D - expensive, do not have a moulded curve so may require stylet to intubate, only low volume high pressure
What is the Murphy eye in ET tubes?
An oval hole in the tube opposite the bevel which allows gases to enter and exit if occluded
Define ataractic
Reduce stress or tension without reducing mental capacity.
(Another word for tranquilliser)
Define psychotropic
Drug that affects how the brain works, causes change in mood, awareness, behaviour, thoughts and feelings
Define agonist
(Opioid)
A drug or substance that binds to a receptor inside a cell or on its surface and causes the same action as the substance that normally binds to that receptor
What are the aims of pre-med
To calm and control the patient for a smooth induction
To provide analgesia throughout surgery
To reduce the amount of induction and maintenance agent needed
To reduce some of the unwanted side effects
To reduce other side effects of anaesthesia
To ensure a smoother recovery
Routes for pre-med administration
SC - good animal tolerance as less painful but slow uptake and not reliable in dehydrated patients
IM - more reliable uptake, fairly good animal tolerance, good onset of action, painful
IV - predictable, very quick onset of action, usually not painful on injection, more difficult to place catheter.
What history should be taken during pre-op checks?
Status of chronic diseases if diagnosed
Changes in bw
Changes in water or food consumption
Shortness of breath, exercise intolerance, coughing
Prev GA hx
Vaccine status
Temperament
What does haematology and biochemistry test for ?
Haem - anaemia and coagulation disorders
Bio - metabolic disorders
ASA grade 1
Minimal risk
Normal healthy animals with no underlying disease
(Young fog presenting for neutering)
ASA grade 2
Slight risk
Mild systemic disturbances with no clinical signs of disease bcs they are able to compensate
Dog with low grade heart murmur not showing signs of cardiac disease
ASA grade 3
Moderate risk
Animals showing signs of mild clinical signs associated with moderate systemic disease
Dog with a heart murmur resulting in reduced exercise tolerance
ASA grade 4
High risk
Animals with pre-existing systemic disease or severe system disturbances that is a constant threat to life
Dog with cardiac arrhythmia causing severe circulatory compromise
ASA grade 5
Grave risk
Animals with life threatening system disease
Dog with GDV
Thiopental (barbiturate)
Made up from a crystalline powder using sterile water to produce a 1.25% or 2.5% solution for small animals.
Can be kept in the fridge for 24hrs once made
Rapid onset but short acting (single dose = 20 mins)
Administer slowly IV
Causes myocardial depression,hypotension, resp depression and compensatory tachycardia
Can cause splenic enlargement
Recovery = re-distribution from brain into body’s fat instead of metabolism. (Hangover)
Not to be given in puppies and kittens under 3mths old
Etomidate (carboxylated imidazole)
NOT licensed in animals
2 formulations: propylene glycol and another in a hyperlipid emulsion
Suitable for animals with severe cardiovascular compromise as minimal effects on hr or inotropy
Minimal effects on resp system.
May cause muscle twitching at induction
Inhibits cortisol production so animals may enter Addisonian crisis
Rapid recovery vis redistribution and hepatic metabolism
Propofol (phenol)
2 preparations: a preservative (benzoyl alcohol) enabling it to be used for 28 days after 1st use and one without a preservative to be discarded immediately.
IV inj - rapid induction lasting 15-20 mins
Rapidly metabolise by liver and other sites.
Can be used as CRI but less suitable in cats as slower liver metabolism (causes oxidative injury to RBCs)
Muscle twitching if used for long duration.
After IV inj may experience drop in bp, cardiac output, resp and poss apnoea
Short duration of action
Alfaxalone (steroid)
Alfaxan 10mg/ml
Suitable for cats and dogs
Route = IM or slowly IV (to avoid resp depression/apnoea)
Maintain anaesthesia through incremental inj or CRI
2 formulations - preservative and non-preservative
Causes myocardial depression and a compensatory inc hr
Recovery can be unpredictable if no premed given
Very rapidly metabolised by liver
Ketamine (dissociative anaesthetic)
Compatible = dogs, cats, rabbits and exotics
Used in combination with alpha-2 agonists, opiate analgesics and benzodiazepines
Administration - IV or IM
Longer shelf life as has preservative
Sch 2 CD
Causes inc hr, minimal changes to cardiac output and resp system
Can cause apneuristic breathing
Eyes remain open and eyelid and corneal reflexes intact
Do not give to patients with impaired renal or hepatic function.
Inc inter-cranial pressure
Halothane (fluothane)
Halogenated hydrocarbon
MAC 0.75% and BG = 2.3
Clear, colourless, needs protection from light
May cause myocardial and resp depression
High levels of adrenaline circulating which may follow cardiac arrest
30% metabolised by liver
Prolonged recovery with prolonged use
Reduces liver blood flow - avoid with liver comprised patients
Isoflurane
Halogenated ether
MAC 1.15% BG = 1.4
Pungent smell - irritant to airways
Rapid induction and recovery
Causes resp and cardiovascular depression
Reduced vascular resistance = vasodilation and a compensatory hr.
Excreted via lungs minimal involvement w liver.
Sevoflurane
Halogenated ether
MAC 2.05% BG 0.6
Odourless, less irritating
Rapid induction and recovery
Allows rapid changes in anaesthesia depth
Reduction in myocardial contractility and arterial bp - induces peripheral vasodilation
Minimal liver metabolism - excreted from lungs
Reacts with soda lime producing a chemical called compound A (toxic to rats)
More expensive than iso
Desflurane
Halogenated ether
MAC 5-10% BG 0.42
Poor inhalation induction due to pungent smell - unsuitable for mask inhalation
Very low solubility - most rapid induction and recovery
Allows rapid changes in anaesthesia depth
Myocardial contractility and resp depression
Excreted by lungs - very little liver metabolism
NOT licensed in animal species
Vaporises very quickly at room temp
Delivery requires a special vaporiser to electrically heat and pressurise gas
Flammable at very high concentrations (>17%)
What equipment/consumables are needed for anaesthesia induction?
Induction agent, reversal agent and analgesia
Clippers and blade
Scissors
Vacuum
Assistant
Laryngoscope
ET tubes
Capnograph, anaesthetic machine, multi parameter, Doppler
IVFT and infusion pump, giving set, extension set, t-connector
Catheter, bung, flush
Swabs and spirit.
Define ‘ABC’ in terms of anaesthesia
AIRWAY - assist in intubating the patient and check the tube is positioned correctly
BREATHING - watch chest and bag to check breathing. Often a short period of apnoea following induction of thiopental, propofol, alfaxalone). May need to ventilate until patient is spontaneous breathing.
CIRCULATION - monitor hr, check for pulse (peripheral pulses give an accurate idea of the peripheral perfusion)
How can you tell a patient is ready for intubation?
Jaw tone is relaxed
Tongue can be pulled out of mouth with no resistance
Attempts to introduce the ET tube don’t result in swallowing or gagging movements
What is the formula for ET tube size?
(BW/4) + 4 = tube size
Can also measure gap in-between nostrils
Dogs = Canine teeth - point of shoulder
Cats and brachycephalic = corner of mouth - point of shoulder
What are the steps of intubation ?
An assistant holds the jaw by the lateral aspect of the mucous membrane under the lips
Use of laryngoscope
Identification of epiglottis
Avoidance of laryngeal spasm
Intubate the patient and check the ETT is correctly positioned
Correct inflation of the cuff (20-30cm H20)
Secure in position
Connection.
When can the ETT be removed in dogs and cats?
Dogs = remove on return of the gag or swallow reflex (in brachycephalic dogs leave as long as poss)
Cats = remove before the swallowing reflex returns - look for signs of arousal; palpebral and pedal reflexes, tail, head and limb movements
What are the normal values for respiration ?
Dog: 10-30 breaths per min
Cat: 20-30 breaths per min
Hypoventilation depth definition
Slows resp rate and a small tidal volume.
Likely to result in hypercapnia and a reduction in O2 saturation.
What is hyperventilation in anaesthesia depth?
Increase in the depth resulting in deep rapid breathing
What is a respiratory monitor
Uses microphones to monitor the depth of breathing.
The monitor produces a tone whose volume is proportional to the depth of breathing.
Adv - both vet and nurse can hear any changes and take immediate action, cost effective
Capnograph
Measures CO2 levels in the airway
Stated as either a % or mmHg
Normal levels: 35-45mmHg or 5-6%
50mmHg = significant respiratory acidosis (brachycephalics may tolerate 50-55mmHg)
What does Wright’s resp monitor measure?
Tidal and minute volume
Pulse oximeter
Measure the amount of saturated O2 in the blood.
Probe shines lights through the tissue and measure the colour of arterial haemoglobin.
>97% is norm
How can the pulse ox be affected by?
Probe squashing tissue and preventing pulsatile blood flow
Abnormal haemoglobin
Intravenous dyes
Patient moving
Vasoconstriction
Interference from ambient light
Skin pigmentation
Electrosurgical equipment
Blood gas analysis
Measures arterial levels of oxygen and carbon dioxide
Indicates the presence of respiratory and metabolic derangements: acid base, ventilation and oxygen
Normal heart rate for dogs and cats.
Dogs: 70-140 beats per min
Cats: 100-200 beats per min
Name the central pulses
Femoral and carotid
Name the peripheral pulses
Metacarpal
Dorsal pedal
Coccygeal
Lingual
Auricular
Theses pulses are more helpful when assessing perfusion as they are more sensitised to changes
Define regular and irregular heart rhythm
Regular - steady constant rhythm
Irregular - variations in timing between beats. Caused by cardiac arrhythmias or inadequate ventricular contractions failing to open aortic semilunar valves.
Reasons for abnormal pulse rates
Lowered rate = myocardial depression caused by drugs, systemic illness and deep anaesthetic
Increased rate = light anaesthetic, stress, pain, pyrexia, hypoxia
Weak = poor circulation, peripheral vasoconstriction, drug effects
Strong and jerky = heart defects and hyper-dynamic states
Define a bounding pulse
An extremely strong and powerful pulse experienced for short durations
Aka as leaping or forceful pulse
Sometimes can be seen pulsing under the skin
Large pulse pressure difference and wide waveform
Can be a sign of heart failure, chronic kidney failure and fluid overload
Define a waterhammer pulse
Aka Corrigan’s, jerky and B-B shot pulse.
Associated with increased stroke volume of the left ventricle and decrease in the peripheral resistance leading to wide pulse pressure.
Pulse strikes the palpating finger with a rapid, forceful jerk and quickly goes.
Caused by the artery suddenly emptying because some of the blood flows back from the aorta into the ventricle.
Found in: aortic incompetence, hyperdynamic states: fever, anaemia and thyrotoxicosis.
The haemoglobin-oxygen dissociation curve
Saturation of haemoglobin with oxygen varies with the partial pressure of oxygen.
At high partial pressures of oxygen, Haemoglobin binds to oxygen to form oxyhaemoglobin (shifts to the left)
As the red blood cells travel to tissues deprived of oxygen the partial pressure of oxygen will decrease and makes the oxyhaemoglobin release the oxygen to form Haemoglobin (shift to the right)
This is affected by increased temp, CO2, lactic acid, DPG, and H (decreased pH)
Where can the mucous membranes be checked?
The gingiva
The conjunctiva
The anus
The vagina or penis
What are the normal values for blood pressure?
Dogs and cats
Systolic: 90-120 mmHg
Diastolic: 55-90 mmHg
MAP: 60-85 mmHg
What causes slow CRT?
Hypotension
Hypovolaemia
Toxaemia
Shock
Haemorrhage
Rough handling of viscera
Oscillometric blood pressure monitoring
(Non-invasive)
Only non-invasive method that measures MAP
Placement: distal limb or tail
Cuff is inflated to above systolic pressure, occluding the blood flow, pressure is then slowly reduced, allowing blood to pulse through the vessel, indicating systolic arterial blood pressure.
A: non-invasive and simple to use. Repeated readings taken every few mins. Provides systolic, diastolic and mean blood pressures.
D: less accurate than Doppler methods in smaller animals although newer machines very accurate
Doppler method (blood pressure monitoring)
Non-invasive
Probe placed on the palmar aspect of metacarpus, cuff is placed above elbow.
The sphygmomanometer measures pressure in the cuff and the Doppler probe senses blood movement within the artery which can be heard.
Cuff inflated to a pressure that occludes systolic pressure, so no pulsing is heard from the probe.
Cuff is deflated, an audible pulsation returns, indicating systolic pressure at the cuff.
A: non-invasive and more accurate than oscillometric.
D: doesn’t provide a continuous reading, has to be manually taken. No accurate diastolic reading is obtained and no MAP.
Invasive arterial reading
Catheter placed into an artery (commonly used - dorsal metatarsal, femoral and carotid)
Catheter should be sutured in place and a 3 way tap attached, a manometer is then attached with another 3 way tap and then a pressure veil and aneroid manometer, the system is then filled with saline, once a reading is required a 20ml syringe filled with saline is attached to the 3 way tap and introduced until there is a pressure reading on the manometer.
The fluid line needs to be flushed periodically to avoid clot formation at the site, this can be seen from the arterial trace wave.
Central venous pressure blood pressure
Invasive
The same as invasive arterial reading but only using the jugular vein and a venous manometer.
The height of the manometer should be in line with the height of the right atrium.
Filling pressure of the central venous reservoir at the level of the right thoracic vena cava
Used to assess fluid balance, hypovolaemia or circulatory overload.
Influenced by changes in intrathoracic pressure. Normal range 0-7cmH2O.
Electrocardiography (ECG)
Detects electrical activity of the heart
The monitor could produce a normal readout when cardiac output is zero, this is known as electromechanical dissociation (aka pulsless electrical activity PEA)
Define the ECG waves
P: depolarisation atria
PR: beginning of atrial depolarisation into ventricular depolarisation. Interval due to slow conduction through AV node.
QRS: ventricular depolarisation
T: repolarisation is hidden by QRS complex.
Causes of arrhythmias
Cardiac disease (macro or microscopic)
Autonomic imbalance
Metabolic derangement (electrolytes)
Drugs and toxins
Sepsis
Trauma
What is abornomal ventricular complexes?
Abnormal rhythm
Wide, often bizarre shape, no P waves and T wave obscure
What are normal temp values?
(Dog, cat, rabbit)
Dog - 38.3 - 39.2
Cat - 38.2 - 38.6
Rabbit - 38.5 - 40
What causes hypothermia during anaesthesia?
A large surgical clip
wet patient prep
Lowered metabolic rate (old)
Lack of movement
Low ambient temp
Insufficient external heat
How can the level of consciousness be measured?
Eye position
Muscle tone
Cranial nerve reflexes
Cardiovascular signs
How can blood loss be measured?
Weight differential of dry and used swabs
Suction bottle contents
Visual observation
Blood analysis
Blood pressure
Formula for calculating blood loss
10 X 10cm swab = 2g
2g X number of swabs used during surgery = dry weight
Subtract dry weight from weight of blood soaked swabs to calculate weight of blood lost
1g of weight = 1ml blood
Blood volumes:
Dogs 88ml/kg
Cats 66 ml/kg
Tourniquets
Bier blocks - used in orthopaedic surgery
Haemorrhage of limb or tail - used as last resort
Max of 15 mins
Potential toxic shock syndrome, haemolysis, ischaemia, muscle and nerve damage, tissue necrosis
Removal of tourniquets leads to decrease in mean arterial bp (due to release of metabolites from ischemic limb into the circulation and dec in peripheral vascular resistance)
Transient inc in EtCO2, dec in temp, central venous oxygen tension seen.
Allowing blood flow back can induce a paradoxical extension of ischemic damage mediated by oxygen free radicals and is known as ‘reperfusion syndrome’
Acute resp distress syndrome, renal and cardiac injury
Venous embolisation may occur (lower limbs especially)
What’s signs should be reported during recovery?
Significant change since resp, pulse, pattern or rate
Level of consciousness
Significant blood loss
Significant changes in bp
Signs of pain/distress
Changes in behaviour/appearance
Temp changes
