VNSA11 Flashcards

1
Q

What does general anaesthesia provide?

A

Muscle relaxation
Analgesia
Unconsciousness

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2
Q

Define general anaesthesia

A

The reversible immobile state that induces amnesia

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3
Q

Name anaesthetic types

A

General anaesthetic
IV induction agents
Inhalation gases
Epidural
Local anaesthetic
Dissociative
Topical
Regional

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4
Q

Local anaesthesia

A

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

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5
Q

Pharmacokinetics of local anaesthetics

A

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

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6
Q

Local anaesthetic drugs

A

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.

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7
Q

Topical anaesthesia (local)

A

Eg sprays, drops, gel or cream
Limited to analgesia of nasal mucous membranes, eye, larynx, penis, vagina, rectum and urethra.

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8
Q

Perineural (regional) block
(Local anaesthetic)

A

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

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9
Q

Intra-articular block (local anaesthetic)

A

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.

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10
Q

Epidural (local anaesthetic)

A

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

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11
Q

Local infiltration block (local anaesthetic)

A

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

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12
Q

Intravenous regional anaesthetic (Bier block)
(Local anaesthetic)

A

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

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13
Q

Dissociative anaesthesia

A

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.

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14
Q

Recovery symptoms of dissociative anaesthesia

A

On recovery patient may present with;
Hypersalivation
Hyperventilation
Tachycardia
Muscle twitches
Paddling of the legs
Curling of the tongue

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15
Q

Physiology of anaesthesia

A

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.

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16
Q

General anaesthesia; effects on the cardiovascular system

A

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

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17
Q

General anaesthesia; effects on the resp system

A

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.

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18
Q

General anaesthesia; effects on the liver

A

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.

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19
Q

General anaesthesia; effects on the kidneys

A

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.

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20
Q

Define MAC

A

Minimum alveolar concentration

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21
Q

What is the minimum alveolar concentration (MAC)

A

Amount required to suppress movement to noxious stimulant in 50% of patients.

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22
Q

About MAC

A

A measure of anaesthetic potency
Potent inhalant agents have a lower MAC.

Dependent on: species, age, temp, disease, CNS depressant drugs, pregnancy

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23
Q

Drug MAC levels

A

Halothane 0.75%
Isoflurane 1.15%
Sevoflurane 2.05%
Desflurane 5-10%

Halothane = most potent

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24
Q

Halothane

A

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

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25
Q

Isoflurane and sevoflurane

A

Low solubility coefficient
Slower absorption into blood, but released readily into brain
Rapid induction of anaesthesia
Agents are eliminated quickly by lungs
Rapid recovery

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26
Q

Drug blood-gas solubility

A

Halothane 2-3
Isoflurane 1.4
Sevoflurane 0.6
Desflurane 0.42

Halothane has a slow induction and Desflurane has quickest recovery

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27
Q

Soluble anaesthetic agents

A

Slow induction, slow recovery

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28
Q

Insoluble anaesthetic agent

A

Rapid induction, rapid recovery

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29
Q

Define critical tension

A

The necessary drug concentration needed in the brain to induce unconsciousness.

(As levels fall below critical tension the animal will regain consciousness)

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30
Q

Define pain

A

A sensory or emotional experience associated with actual or potential tissue damage

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31
Q

Analgesia

A

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

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32
Q

What 3 categories is pain split into?

A

Physiological
Inflammatory
Neuropathic

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33
Q

Physiological pain

A

Early warning device of potentially painful stimuli
Pain is proportional to stimulation
Pain experienced is localised
“Normal” pain pathway activation

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34
Q

Inflammatory pain

A

Pain associated with changes to pain pathway
-heightened pain sensitivity
-skin incision causes inflammation and tissue damage
Control of disease process causing pain hypersensitivity

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35
Q

Neuropathic pain

A

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)

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36
Q

Peripheral sensitisation

A

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

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37
Q

Central sensitisation

A

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

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38
Q

Pre-emptive analgesia

A

Analgesia provided before noxious stimuli
Prevents “sensitisation” or “wind-up”
Analgesia that has taken place after this is less effective

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39
Q

Multimodal analgesia

A

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

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40
Q

Physiological effects of pain

A

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

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41
Q

Response to pain
(Spinal, medullary, hypothalamic, cortical)

A

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.

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42
Q

Routes for administration of analgesia

A

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%).

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43
Q

Analgesia in rabbits and rodents

A

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

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44
Q

Analgesia in birds

A

Opioids used (kappa opioids receptors more effective than uu)

Response between species varies

NSAIDs used - nephrotoxicity and gastric ulceration seen. Repeated doses are unadvisable.

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45
Q

Define tidal volume

A

The amount of air that moves in or out of the lungs with each respiratory cycle

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46
Q

Define minute volume

A

Amount of gas inhaled or exhaled from the lungs in 1 minute

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47
Q

Expiratory reserve volume (ERV)

A

Amount of air you can forcefully exhale past a normal tidal expiration

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48
Q

Inspiratory reserve volume (IRV)

A

Amount of air that can be taken into the lungs (above the tidal volume) upon forceful inspiration

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49
Q

Define residual volume

A

The volume of air remaining in the lungs after maximum forceful expiration

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50
Q

Define vital capacity

A

Maximum amount of air a person can expel from the lungs after a maximum inhalation
(ERV + IRV + tidal volume)

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51
Q

Define total lung capacity

A

The amount of air the lung can contain at the height of maximum inspiratory effort
(Residual volume + vital capacity)

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52
Q

Define functional residual capacity (FRC)

A

The volume in the lungs at the end expiratory position
(ERV + residual volume)

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53
Q

Define physiological (anatomical) dead space

A

Volume of air in the respiratory zone that doesn’t take part in gas exchange
(Tranches down to the terminal bronchioles)

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54
Q

Define equipment dead space

A

Dead space resulting from devices placed between the ET tube and the y-piece of the breathing circuit

55
Q

Define compliance

A

Measurement of pressure in a breathing system.
Affects the tidal volume of gas the patient receives.
Increases in compliance can decrease tidal volumes.

56
Q

What is the difference between a sedative and a tranquilliser?

A

Sedative - promotes calm and induces sleep

Tranquilliser - reduces tension or anxiety but does not induce sleep

57
Q

What is a narcotic?

A

Drug that in moderate doses dulls the senses, relieves pain and induces sleep but in excessive doses causes stupor, coma or convulsions

58
Q

Define neuroleptanalgesia

A

Joint administration of a tranquilliser and an analgesic
Relief of surgical pain

59
Q

What is the anaesthetic sparing effect?

A

Some medical agents have the ability to reduce the need for the full anaesthetic agent dose.
(Premeds and N20)

60
Q

What is the second gas effect?

A

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

61
Q

What is diffusion hypoxia?

A

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.

62
Q

What is the triad of balanced anaesthesia

A

-loss of consciousness
-muscle relaxation
-analgesia

63
Q

What is so important about pre-medication

A

-calms the patient before induction
-reduces amount of anaesthetic needed for induction and maintenance
-contributes to the triad of anaesthesia
-analgesia
-smoother recovery

64
Q

Neuroleptanalgesia

A

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

65
Q

Dissociate anaesthetics

A

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

66
Q

Define TIVA

A

‘’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

67
Q

Define PIVA

A

‘’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

68
Q

Define potency

A

Alveolar concentration of inhalation anaesthetic that prevents movement in 50% of animals in response to a noxious stimulus

69
Q

Define volatility

A

Liquid at room temp but evaporate easily for administration by inhalation
(Nitrous)

70
Q

Define solubility in tissues

A

Measure of how an agent is taken into tissues or organs

71
Q

Define flammability

A

A measure of how quickly a specific material is capable of catching fire and burning

72
Q

Define chemical stability

A

The materials ability to withstand change from chemical contact
Drugs ability to remain in the same chemical form when exposed to various environmental conditions.

73
Q

Depth of anaesthesia

A

Depth depends on concentration in the brain.
Most inhalant agents cross the blood brain barrier with ease as they’re lipid soluble.

74
Q

Steps of anaesthesia depth

A
  1. Inhaled into lungs
  2. Cross the alveolar membrane and pulmonary capillary endothelium
  3. Dissolve in the blood and taken via pulmonary circulation to the left hand side of the heart and all body tissues
  4. Cross blood-brain barrier
  5. Exert their effect (unconsciousness)
75
Q

Ideal properties of inhalation agents

A

-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

76
Q

Oxygen (carrier gas)

A

Essential for supporting life
Administered at concentrations between 33-100%
Explosive combination with flammable agents

77
Q

Nitrous oxide (Carrier gas)

A

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

78
Q

Neuromuscular blocking agents (NMBA) what does it provide

A

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

79
Q

How can muscle relaxation be provided ?

A

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

80
Q

What caution is needed when using NMBAs

A

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

81
Q

Depolarising agents VS non-depolarising agents

A

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.

82
Q

What are the 4 stages to anaesthesia?

A

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

83
Q

What is the pin index system?

A

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

84
Q

What is a schrader probe?

A

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

85
Q

What is a Boyle’s bottle?

A

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

86
Q

Calibrated vaporiser

A

“TEC’ / Penlon” types

Produce known anaesthetic vapour concentration regardless of temp and fresh gas flow rate
Serviced annually
Anaesthetic agent specific

87
Q

Vaporisers

A

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.

88
Q

Name the low oxygen warning devices

A

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

89
Q

What is a oxygen-nitrous oxide proportioning device

A

Anaesthetic machines will not supply nitrous oxide without oxygen.
Preventing supply of hypoxic mixture to patient

90
Q

What is active scavenging

A

Preferred technique
Uses extractor fans to create negative pressure
Pressure break incorporated to prevent excessive negative pressure on patient (Barnsley receiver)

91
Q

What is passive scavenging ?

A

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

92
Q

What is active-passive scavenging

A

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

93
Q

What is the full weight of an oxygen cylinder

A

137 bar

94
Q

What is the weight of a nitrous oxide cylinder ?

A

44 bar

95
Q

What are the 3 main functions of an anaesthetic machine?

A

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

96
Q

Define resistance

A

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

97
Q

Define mechanical dead space

A

Too much equipment between the patient and the anaesthetic machine.

98
Q

Define circuit drag

A

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.

99
Q

What is an open anaesthetic circuit?

A

Lint or gauze placed on the nose of the animal and volatile anaesthetic agent dropped onto the material.

100
Q

What is a semi-open anaesthetic circuit?

A

Same as open but gauze is placed inside a mask and attached to oxygen

101
Q

What is a semi-closed circuit?

A

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.

102
Q

What is a closed circuit?

A

Same as a semi-closed circuit but soda lime is used to absorb carbon dioxide so the patient can re-breathe the same gas.

103
Q

Semi-closed (non-rebreathing) circuits

A

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.

104
Q

What circuits are Mapleson A?

A

Magill and lack

105
Q

What circuits are Mapleson D?

A

Modified Bain
Modified Ayers T-piece

(Has a bag and APL valve)

106
Q

What types of circuits are Mapleson E?

A

Ayres-T

(No bag and no APL)

107
Q

What type of circuits are Mapleson F?

A

Modified Ayres-T (Jackson Rees modification)

(Has a bag with a hole in it and no APL)

108
Q

What are the indicators for soda lime?

A

Pink soda lime turns white when exhausted
White soda lime turns purple when exhausted

109
Q

Advantages and disadvantages of red rubber ET tubes

A

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

110
Q

Advantages and disadvantages of PVC ET tubes

A

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.

111
Q

Advantages and disadvantages of silicone ET tubes

A

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

112
Q

What is the Murphy eye in ET tubes?

A

An oval hole in the tube opposite the bevel which allows gases to enter and exit if occluded

113
Q

Define ataractic

A

Reduce stress or tension without reducing mental capacity.
(Another word for tranquilliser)

114
Q

Define psychotropic

A

Drug that affects how the brain works, causes change in mood, awareness, behaviour, thoughts and feelings

115
Q

Define agonist

A

(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

116
Q

What are the aims of pre-med

A

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

117
Q

Routes for pre-med administration

A

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.

118
Q

What history should be taken during pre-op checks?

A

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

119
Q

What does haematology and biochemistry test for ?

A

Haem - anaemia and coagulation disorders
Bio - metabolic disorders

120
Q

ASA grade 1

A

Minimal risk
Normal healthy animals with no underlying disease
(Young fog presenting for neutering)

121
Q

ASA grade 2

A

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

122
Q

ASA grade 3

A

Moderate risk
Animals showing signs of mild clinical signs associated with moderate systemic disease

Dog with a heart murmur resulting in reduced exercise tolerance

123
Q

ASA grade 4

A

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

124
Q

ASA grade 5

A

Grave risk
Animals with life threatening system disease

Dog with GDV

125
Q

Thiopental (barbiturate)

A

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

126
Q

Etomidate (carboxylated imidazole)

A

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

127
Q

Propofol (phenol)

A

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

128
Q

Alfaxalone (steroid)

A

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

129
Q

Ketamine (dissociative anaesthetic)

A

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

130
Q

Halothane (fluothane)
Halogenated hydrocarbon

A

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

131
Q

Isoflurane
Halogenated ether

A

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.

132
Q

Sevoflurane
Halogenated ether

A

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

133
Q

Desflurane
Halogenated ether

A

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%)