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Vet Nurse Small Animal Diploma CQ > Anaesthesia (SA11) > Flashcards

Anaesthesia (SA11) Flashcards

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1
Q

What are the 3 main routes anaesthesia drugs are administered?

A
  • Intravenous
  • Intramuscular
  • Inhalation
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2
Q

Why is it important to monitor anaesthetised patients closely and understand how to identify changes that may occur?

A
  • Many homeostatic systems are suppressed
  • Prevent long-term effects of anaesthesia
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3
Q

What is the autonomic nervous system?

A
  • Regulates involuntary processes
  • Comprised of sympathetic and parasympathetic
  • Many processes suppressed under GA
  • Expect return to normal function quickly in healthy patients
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4
Q

What does the sympathetic nervous system do?

A
  • Dilates pupils
  • Inhibits salivation
  • Accelerates heart beat
  • Dilates bronchi
  • Inhibits digestion
  • Stimulates glucose release in liver
  • Stimulates epinephrine + norepinephrine release in kidneys
  • Inhibit peristalsis and secretions in intestines
  • Relaxes bladder
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5
Q

What does the parasympathetic nervous system do?

A
  • Constricts pupils
  • Stimulates salivation
  • Slows heart beat
  • Constricts bronchi
  • Stimulates digestion
  • Stimulates bile release in liver
  • Stimulates peristalsis and secretion in intestines
  • Contracts bladder
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6
Q

What is high vagal tone?

A

Parasympathetic nervous system more dominant, seen in brachycephalics

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7
Q

What order will inspired air pass through the respiratory system?

A
  • Nasal cavity
  • Pharynx
  • Larynx
  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
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8
Q

What controls the respiratory cycle?

A
  • Chemoreceptors detect changes in O2 and CO2
  • High CO2 lowers blood pH = more acidic
  • Disrupting acid base balance
  • Medulla changes depth and rate to expel CO2
  • pH will return to normal
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9
Q

Where are chemoreceptors found?

A
  • Walls of aorta and carotid artery
  • In the medulla
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10
Q

What prevents over inflation of the lungs?

A
  • Hering-Bruer reflex
  • Stretch receptors in walls of bronchi + bronchioles
  • Monitor stretching during inspiration
  • Send impulses via vagus nerve to brain
  • inspiratory centre prevents further inspiration
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11
Q

Gaseous exchange

A
  • Only occurs in alveoli
  • One cell thick walls + lots of capillaries
  • Gases move by diffusion, high to low concentration
  • O2, air into blood. CO2, blood into air
  • Water vapour lost in process
  • Inhalation anaesthesia reliant on effectiveness of this to be administered and excreted from the body
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12
Q

How can tissue hypoxia be prevented?

A
  • Organ damage can occur even if tissues are deprived of oxygen for short periods
  • Critical oxygen tension level must be provided for metabolic consumption
  • 2-7mls/kg/minute for cats and dogs
  • Not recommended
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13
Q

Acid base balance and respiration

A
  • CO2 high, carbonic acid released
  • Hydrogen ions released, decrease in pH
  • Respiratory acidocis
  • CO2 low, hydrogen ions lost, increases pH
  • Respiratory alkalosis
  • Even slight pH variations cause severe effects
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14
Q

How may respiratory disorder affect anaesthesia?

A
  • Impaired diffusion of inhaled gases
  • Risk of hypoxia from impaired gaseous exchange
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15
Q

Hypoxaemia

A
  • Low level of oxygen in blood
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16
Q

Hypoxia

A
  • Low oxygen in certain area
  • E.G. tissue hypoxia
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17
Q

What is critical oxygen tension level?

A
  • Oxygen level required for metabolic consumption to prevent tissue hypoxia
  • 2-7ml/kg/minute for dogs and cats
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18
Q

What is respiratory acidosis?

A
  • High levels of CO2
  • High levels of carbonic acid
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19
Q

What is respiratory alkalosis?

A
  • High levels of O2
  • Low levels of CO2
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20
Q

What is hypercapnia?

A

Raised ETCO2

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21
Q

What is hypocapnia?

A

Low ETCO2

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22
Q

What is the normal CO2 level in patients?

A

35 - 45 mmHg

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23
Q

What causes hypercapnia?

A

Hypoventilation

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24
Q

What causes hypocapnia?

A

Hyperventilation

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25
Q

What is cardiac output?

A

Amount of blood heart pumps each minute

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26
Q

What is the cardiac output formula?

A

Heart rate x stroke volume

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27
Q

What is the blood pressure formula?

A

Cardiac output x systemic vascular resistance

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28
Q

What is systemic vascular resistance?

A

Degree of vasocontriction/dilation

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29
Q

How does the body control blood pressure?

A
  • Baroreceptors (stretch receptors)
  • In aortic arch, left + right atria, left ventricle, pulmonary circulation
  • Medulla detects changes and corrects BP
  • Alteration in HR or vasoconstriction/dilation of blood vessels
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30
Q

Why is blood pressure monitoring during GA important?

A
  • Low BP reduces tissue and organ perfusion
  • Can cause long term damage
  • Anaesthesia often causes hypotension
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31
Q

What does the renal system control?

A
  • Blood pressure
  • Blood volume
  • Electrolyte balance
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32
Q

Why is good renal function important in GA?

A
  • Blood supply to kidneys may reduce during GA
  • Kidneys need to excrete some anaesthetic drugs
  • NSAIDs can reduce renal blood flow
  • Good to check renal function before GA
  • Monitor and maintain BP helps ensure adequate renal perfusion
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33
Q

Albumin and anaesthesia

A
  • Hepatic system produced albumin
  • Many anaesthetics and analgesics transported in blood bound to albumin
  • If low albumin, higher levels of drugs ‘free’ in blood
  • If low albumin, lower drug doses required
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34
Q

Liver and anaesthesia

A
  • Anaesthetics can affect blood supply to liver and impair functions
  • Liver metabolises many anaesthetic agents
  • Liver disease can cause prolonged recovery times
  • Fat accumulating in liver affects funtion
  • Diabetes mellitus, chushings, hypothyroidism
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35
Q

The brain and anaesthesia

A
  • Blood brain barrier selectively permeable
  • Water, CO2, O2, lipophilic molecules pass easily
  • Anaesthetic agents must be lipophilic to act on brain
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36
Q

Shock and anaesthesia

A
  • Cardiac output too low, low blood flow to tissues
  • Leads to cell damage, organ damage and death
  • Haemorrhage and dehydration common causes
  • Initially pale MMs, increased HR, low BP, reduced urine output
  • Must be identified quickly and treated aggressively
  • Will impact excretion of drugs, can further complicate condition
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37
Q

Sight hounds and anaesthetics

A
  • Very sensitive to some drugs
  • Barbiturate induction agents (Thiopentone)
  • Redistributed around body, including in fat
  • Recovery delayed due to low body fat
  • Reduced specific liver enzymes needed to metabolise certain drugs
  • Further slowing recovery
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38
Q

Bracycephalics and anaesthesia

A
  • Bracys of any species at risk of airway obstruction
  • Extra airway management care, close monitoring after pre-med
  • Many are hypoxic at point of anaesthesia
  • May require oxygen pre and post surgery
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39
Q

Collies and anaesthetics

A
  • Some have gene mutation = sensitive to some drugs
  • Gene affects blood brain barrier, higher levels can reach the brain
  • Extra care taken with doses of certain sedatives and opioids
  • Methadone and buprenorphine
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40
Q

What is the herring breuer reflex do?

A
  • Avoid over inflation of lungs
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41
Q

What is anaesthesia

A

A controlled temporary loss of sensation or awareness for medical purposes

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42
Q

What are the 2 types of anaesthesia?

A
  • General
  • Local
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43
Q

What is general anaesthetic?

A

Reversible immobile state that induces amnesia

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44
Q

What is local anaesthetic?

A
  • Application of anaesthetic to specific area of the body
  • Usually with sedation or GA in animals
  • Including local in protocols reduces dose of GA drugs, increasing safety
  • Significant for analgesia
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45
Q

Why is anaesthesia needed?

A
  • Welfare reasons
  • Legal obligations
  • Facilitate surgery - immobilise and muscle relaxation
  • To control disease - seizures
  • Euthanasia purposes
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46
Q

What is the order of signs in local anaesthetic overdose?

A

GI signs
Nervous system signs
Cardiac signs

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47
Q

Local anaesthetic safety

A
  • Toxicity occurs with large doses
  • Cats more susceptible to toxicity than dogs
  • May cause seizures, CNS depression, hypotension, bradycardia and cardiac arrest
  • Patients can injure selves due to lack of sensation on recovery
  • Care taken in dental blocks to avoid tongue, patients may chew own tongue otherwise
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48
Q

What are the 3 local anaesthetic routes?

A
  • Topical
  • Infiltration
  • Regional
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49
Q

What is infiltration local anaesthesia?

A
  • Low concentrations anaesthetic agents injected intradermally, subcutaneously or intramuscularly
  • Loss of sensation superficial and localised
  • Mostly used around surgical sites prior to surgery
  • Must not be administered IV, aspirate before injecting to check for blood
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50
Q

Why is adrenaline added to local anaesthetic agent?

A
  • Adrenaline vasoconstricts
  • Not carried away in blood
  • Increases duration of local anaesthetic action
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51
Q

What are other specific local anaesthetic blocks used in practice, other than intradermally?

A
  • Intra-testicular
  • Splash blocks
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52
Q

What is regional anaesthesia?

A
  • Nerve supply to region of body is blocked
  • Reduces depth of GA needed, increases safety
  • Nerve must be easily located and accessible
  • Can use nerve stimulator or ultrasound to locate
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53
Q

Brachial plexus block

A
  • Analgesia distal to elbow
  • Good for distal forelimb procedures
  • Toe amp, carpal surgery; arthrodesis, fracture repair
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54
Q

Femoral and sciatic nerve block

A
  • Analgesia distal to mid shaft of femur
  • Good for stifle and hock surgeries
  • Cruciate ligament surgery, meniscus surgery, luxating patella, hock arthrodesis, fracture repairs
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55
Q

Lumbosacral epidural

A
  • Analgesia caudal to thoracolumbar junction
  • Good for hind quarter othopaedic surgery or perineal area
  • Caesarean section
  • Can use morphine only for abdominal surgery analgesia
  • Epidural catheters can be placed to continue analgesia into recovery
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56
Q

Intercostal nerve block

A
  • Analgesia post throacic surgery or trauma
  • Blocks easily placed prior to closing thoracic cavity as easy nerve visualisation
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57
Q

Maxillary and mandibular blocks

A
  • Different areas of jaw blocked depending on placement
  • Useful for dental procedures or jaw surgery
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58
Q

Intra-articular blocks

A
  • Local injected into joint
  • Often used post joint surgery or analgesia for arthoscopy
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59
Q

What is a wound catheter?

A
  • Placed at end of surgery, allows local infused into area at regular intervals following surgery
  • Care of patient interference
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60
Q

What is meant by ‘balanced anaesthesia’

A
  • Synergistic drugs in combination to reduce doses and improve safety
  • Triad of anaesthesia; unconsciousness, analgesia, muscle relaxation
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61
Q

Who can administer anaesthesia?

A
  • Induction of specific quantity can be administered by vet, RVN, SVN under supervision
  • Incremental induction only by vet
  • Maintaining anaesthesia responsibility of vet
  • Monitoring + moving dials suitably trained person
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62
Q

Tachycardia

A

Increased heart rate

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63
Q

Bradycardia

A

Decreased heart rate

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64
Q

Bradypnoea

A

Decreased respiratory rate

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65
Q

Tachypnoea

A

Increased respiratory rate

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66
Q

Apnoea

A

Lack of breathing

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67
Q

Hypotension

A

Decreased blood pressure

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68
Q

Hypertension

A

Increased blood pressure

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69
Q

Hypovolaemia

A

Decreased blood volume

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70
Q

Dog heart rate

A

70 - 140 bpm

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71
Q

Cat heart rate

A

100 - 200 bpm

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72
Q

Dog respiratory rate

A

10 - 30 bpm

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73
Q

Cat respiratory rate

A

20 - 30 bpm

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74
Q

Tidal volume

A

Volume of gas exhaled in one breath
- BW x 10 / 15mls
- <10kg = 15mls / kg
- >10kg = 10mls / kg

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75
Q

Minute volume

A

Volume of gas exhaled in one minute
- Tidal volume x respiratory rate

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76
Q

Residual volume

A

Volume of air left in lung after forced respiration
- Prevents collapse of respiratory collapse

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77
Q

Atelectasis

A

Collapsed lung or lobe
- Alveoli deflate and become filled with fluid

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78
Q

Risks of atelectasis

A
  • Associated with trauma
  • Penetrating injury or RTA
  • Known risk of anaesthesia
  • Specific anaesthetic risks
  • Pattern of respiration change
  • Altered gaseous exchange
  • Longer surgery
  • Use of mechanical ventilators
  • Extended period of lying on one side
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79
Q

Dead space

A
  • Air that does not reach alveoli so is not involved in gaseous exchange
  • More risk in smaller patients with lower tidal volume
  • More dead space, lower alveolar ventilation, increased CO2 levels
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80
Q

Anatomical and mechanical dead space

A
  • Anatomical; air in upper airway, trachea and bronchi to avoid collapse
  • Can’t control or alter this
  • Mechanical; gas in breathing equipment from end of patient airway to where ‘to and fro’ movement of breaths occur
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81
Q

Minimising mechanical dead space

A
  • Cut ET tubes to size
  • Avoid extra lengths of tubing or connectors
  • Heat moisture exchangers + capnography will contribute to this
  • Correct fresh gas flow rates
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82
Q

Cardiac arrhythmia

A

Abnormal heart rhythm

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83
Q

Sinus arrhythmia

A

Heart rate increase and slow with respiration
Normal in healthy dogs

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84
Q

Pulse deficit

A

Heart rate and pulse rate don’t match
- Usually lower pulse rate
- Indicative of sever cardiac problems

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85
Q

Vagal tone

A

Activity of vagus nerve affecting heart rate and vasoconstriction/dilation
- Increased vagal tone = lower heart rate
- Increased vagal tone common in brachys
- IV prone to very low heart rate under GA

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86
Q

Syncope

A

Fainting due to sudden drop in heart rate and blood pressure
- Vagal response
- Common in boxers

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87
Q

Inhalation agents

A

Produce anaesthesia by inhalation
- Liquids or gases

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88
Q

Volatile anaesthetic agents (VAA)

A

Liquids at room temperature
- Require conversion to vapour
- Isoflorane

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89
Q

Anaesthetic sparing

A

Using local and analgesia to reduce required anaesthetic depth for surgical procedures

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90
Q

Second gas effect

A

Use of nitrous oxide gas as well as volatile agent
- Increases uptake rate of volatile agent

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91
Q

Minimum alveolar concentration

A
  • MAC
  • Min concentration of inhaled anaesthetic when 50% of patients will not respond to stimulus
  • Indicates if need higher or lower concentrations
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92
Q

Emetic drug

A
  • Causes vomiting
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93
Q

Anti-emetic drug

A
  • Prevents vomiting
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94
Q

Analeptic drug

A
  • Central nervous system stimulant
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95
Q

Analgesic drug

A

Pain relief

96
Q

Ecbolic drug

A
  • Initiates uterine contractions
97
Q

Hypnotic drug

A
  • Sleep inducing
98
Q

Amnesic drug

A
  • Partial or full memory loss
99
Q

Muscle relaxant drug

A
  • Decreases muscle tone
100
Q

Ataracric drug

A
  • Calms or tranquilises
101
Q

Anti-sialagogue drug

A
  • Stops salivation
102
Q

Spasmolytic drug

A
  • Relieves spasms or slows gut contractions
103
Q

Neuroleptanalgesia/anaesthesia

A
  • Opioid and sedative (should be ACP)
  • Produces profound sedation and analgesia
104
Q

Dissociative drug

A
  • Produces detached states
105
Q

Narcotic drug

A
  • Dulls senses
  • Numbs pain
  • Induces deep sleep
106
Q

What is premedication?

A
  • Part of all anaesthetic protocols
  • Differ dependent on patient and surgery
  • Contribute to triad of anaesthesia
  • Can produce very different effects
  • Important to know and understand effects to properly monitor
107
Q

What are the aims of premedication?

A
  • Calm patient
  • Reduce stress
  • Reduce anaesthetic drugs needed
  • Contribute to balanced anaesthesia
  • Provide analgesia
  • Smooth recovery
  • Reduce side effects from anaesthetic drugs
  • Reduce autonomic side effects
108
Q

Why is it important for premedications to calm the patient and reduce stress?

A
  • Reduce struggle so reduce adrenaline
  • Can effect heart
  • Some anaesthetic drugs sensitise heart to adrenaline and lead to higher risk of arrhythmias
109
Q

Why is it important for premedications to reduce autonomic side effects?

A
  • Parasympathetic effects like salivation or bradycardia
  • Some agents are added to prevent these
110
Q

Why is it important for premedications to reduce side effects from other anaesthetic medications?

A
  • Nausea is common side effect
  • Some premeds have anti-emetic properties
111
Q

What factors need to be considered when selecting premedication protocols for patients?

A
  • Species and breed; considerations, licenses
  • Temperament; route of administration
  • Underlying disease/clinical history/current medication/previous reactions
  • Age; geriatric = disease more likely
  • Lab results; organ dysfunction, excretion route
  • Type of surgery; how painful? muscle relaxation
  • Duration of surgery; how long need to last for
112
Q

What types of drugs are used in premedications?

A

Sedation
Analgesia
Anti-muscarinics

113
Q

What factors may change route of induction?

A
  • Medication
  • Temperament
  • Speed of onset needed
    Must give sufficient time to see full benefits
114
Q

What are the main groups of sedative agents?

A
  • Phenothiazines
  • Benzodiazepnes
  • Alpha 2 agents
  • Dissociatives
115
Q

What is the only licensed veterinary phenothiazine?

A

Acepromazine (ACP)
- Widely used for premed
- Synergistic with opioids
- Lasts 6 hours; will smooth recovery
- Slower onset
- Can be given IV, IM and SC
- More effective if animals is relaxed
- Not reliable for aggressive animals and cats
- Neuroplept effect in higher doses - heavy sedation

116
Q

What are the physiological effects of acepromazine?

A
  • Prevent adrenaline induced arrhythmias
  • Anti-emetic effect
  • Antihistamine
  • Vasodilation leading to hypotension
  • Vasodilation + hypothalamus effects = hypothermia
  • Boxers have known sensitivity; may collapse
  • Decreased seizure threshold
  • Decreased PCV due to splenic sequestrum; avoid in anaemic patients.
117
Q

What are the benzodiazepines that are widely used in veterinary medicine?

A
  • Diazepam; licensed vet product (Ziapam)
  • Midazolam; unlicensed (Hypnovel)
118
Q

Benzodiazepines for premedication use

A
  • Not reliable sedation in healthy animals
  • May cause excitement
  • More reliable sedation in sick or very young
  • Anxiolytic effect
  • Often used in combination with other agents
  • Can cause appetite stimulation in some animals
119
Q

Physiological effects of benzodiazepines

A
  • Minimal effects on cardiovascular; good for critically ill
  • Muscle relaxation; useful when using ketamine
  • Anticonvulsant effects; useful if increased risk of seizures
120
Q

What are the widely used licensed veterinary alpha-2 agonists?

A
  • Medetomidine (domitor, sedator, dorbene)
  • Xylazine (rompun, chanazine, nerfasin)
  • Dexmedetomidine, contains one isomer of medatomidine (dexmedased, dexdomitor)
121
Q

Alpha-2 agonists as premedications

A
  • Can be antagonised using atipamezole
  • Reliable, profound sedation
  • Synergistic with opioids, allowing lower doses for higher sedation levels
  • Profound drug sparing effects, 50% in maintenance anaesthetic agents
  • Marked cardiovascular effects
  • Typically used in healthy patients
122
Q

Physiological effects of alpha-2 agonists

A
  • Reduces hepatic blood flow, don’t use in hepatic disease
  • Can cause vomiting, more likely with xylazine
  • Don’t use in occular, increased intercranial pressure or some GI surgeries.
  • Xylazine can cause cardiac arrhythmias
  • Cyanosis may be seen due to peripheral blood pooling
  • Ecbolic effect; don’t use in pregnant animals
  • Vasoconstriction; less risk of hypothermia
  • Good muscle relaxation
  • Short duration analgesia (45-60 minutes)
  • Increases urine production
  • Suppresses insulin secretion; hypergyclaemia
123
Q

What is the dissociative drug used in veterinary anaesthesia?

A
  • Ketamine
  • Used for premed, induction or analgesia
  • Schedule 2 controlled drug, record + lock away
  • Good sedation when combined with other agents
  • Excellent somatic analgesia
  • Good drug sparing properties
  • Often combined with benzodiazepines in cats for profound sedation
  • Produces superficial sleep with amnesic properties
124
Q

Physiological effects of dissociative ketamine

A
  • If used alone, can induce seizures, especially in dogs
  • Eyes remain open and position may not alter
  • Eye position unreliable indicator, use corneal lube
  • Stimulates cardiovascular; increase CA + BP
  • Increases myocardial oxygen demand but direct myocardial depressant
  • Increases intercranial pressure
  • If used alone, increases muscle tone and rigidity
  • Hallucinogenic effects in recovery, need dark, quiet environment
125
Q

Most anti-cholinergics are …

A

Anti-muscarinics

126
Q

What are anti-cholinergics used in practice?

A
  • Atropine and glycopyrrolate
  • Atropine is more commonly used as cheaper, licensed and will reduce more secretions
  • Not routinely used in premeds, can be added for specific reasons
127
Q

Physiological effects of anti-cholinergics

A
  • Reduce respiratory secretions + salivation
  • Useful for some throat surgeries or ETT blocked
  • Increase HR in high vagal tone or if bradycardia is effect from other drug (opioids)
  • Common in crash kit, used in emergencies
  • Prevent bradycardia in brachycephalics
  • Don’t treat bradycardia from alpha-2 agonsits
  • Pupil dilation in eye surgery
128
Q

Opioids used in practice

A
  • Common in premed
  • Classified by receptor act on; mu, kappa, delta
  • and whether effect is full, partial or antagonistic
  • Full mu agonists; schedule 2; methadone, fentanyl, morphine - most effective analgesia
  • Partial agonists; schedule 3; buprenorphine - not as effective
  • Mixed agonist/antagonist; kappa agonist/mu antagonist - butorphanol; schedule 4; some analgesia, good sedation
129
Q

What side effects should be monitored for after premedication?

A
  • Hypothermia is high risk after ACP
  • Bradycardia and hypotension
  • Airway patency; especially in bracycephalics
  • High risk require more intense monitoring
  • ECG, pulseoximetry or oxygen therapy
130
Q

How can we ensure premedications are used safely?

A
  • Weigh all patients for accurate doses
  • Give at correct time
  • Record drugs + times given on forms
  • Calm, quiet environment for max effect
  • pre-existing conditions and medications noted clearly on forms + considered
  • Record baseline observations before giving any medications
131
Q

What is apneustic breathing?

A

Expiratory pause is normal
Apneustic is an inspiratory pause

132
Q

What are the 3 different induction techniques?

A
  • Inhalation
  • IV
  • IM
133
Q

What factors may influence the choice of anaesthetic agent?

A
  • Species
  • Temperament
  • Protocol and drugs
  • Age of patient
134
Q

What are the methods of inhalant induction?

A
  • Chamber
  • Mask
135
Q

What are the disadvantages of inhalant induction?

A
  • Stressful
  • Restraint difficult when masking
  • Health and safety with leakage
  • May breath hold or salivate excessively
136
Q

What must injectable anaesthetic agents be to work?

A

Lipophilic so they are able to cross the blood brain barrier

137
Q

What is alfaxalone

A

Steroid anaesthetic agent

138
Q

What species is alfaxalone licensed for?

A

Cats
Dogs
Rabbits

139
Q

How can alfaxalone be administered?

A

Licensed IV
Can give IM

140
Q

Physiological effects of alfaxalone

A
  • Minimal effects on blood pressure
  • Possible apnoea on induction
  • Can maintain anaesthesia incremental or CRI
  • Excretion via hepatic route
  • Minimal effects on neonates and rapid maternal recovery in caesareans
  • Safely used on consecutive days
141
Q

What is propofol?

A

Phenolic compound

142
Q

What is thiopentone?

A

Barbiturate anaesthetic compound

143
Q

What are the contraindications for Thipentone?

A
  • Sight hounds as less fat
  • Splenectomy as enlarged spleen
  • Skin sloughing if out of IV due to alkaline
144
Q

What is ketamine?

A

Dissociative

145
Q

What are the 4 main ways to maintain anaesthesia?

A
  • Inhalant gas
  • Total intravenous anaesthesia (TIVA)
  • Partial intravenous anaesthesia (PIVA)
  • Injectable agents intramuscularly
146
Q

What are the advantages of inhalant anaesthesia?

A
  • Usually protected airway, oxygen easily supplied
  • Depth easy to control
  • Recovery not dependent on drug metabolism as mainly excreted via exhalation
  • Rapid recovery times
147
Q

What are the disadvantages of inhalant anaesthesia?

A
  • Anaesthetic machine and trained staff required
  • Scavenging system required
  • Atmospheric pollution during recovery
  • Inhalant gasses are greenhouse gasses so contribute to damage of ozone layer
148
Q

Volatile agents

A
  • Liquid at room temperature, vaporised
  • Isoflurane and Sevoflurane
  • Carried in another gas; oxygen, nitrous oxide or medical air - vapour at room temp so in gas canisters
149
Q

Delivery of inhalant agents

A
  • Via breathing system
  • ## Passes through lungs, alveolar membrane and into blood stream
150
Q

MAC

A
  • Minimum alveolar concentration of inhaled anaesthetic
  • Potency of agent
  • Lower MAC = Less concentration of agent required
  • Impacted by many factors; premeds used
151
Q

What is the MAC value of Halothane?

A

0.75

152
Q

What is the MAC value of Isoflurane?

A

1.15

153
Q

What is the MAC value of Sevoflurane?

A

2.05

154
Q

What is the MAC value of Desflurane?

A

5-10

155
Q

Solubility in blood of inhalant agents

A
  • Determines speed of induction and recovery
  • Greater solubility, slower onset of action
  • Newer agents less soluble for quicker induction and recovery
156
Q

Another word for solubility of drugs?

A

Blood gas partition co-efficient

157
Q

Factors effecting gaseous recovery

A
  • Concentration of anaesthetic gas
  • Alveolar ventilation, quality breathing
  • Agent solubility in blood
  • Cardiac output
158
Q

Nitrous oxide

A
  • Carrier gas, vapor at room temp
  • Supplied in blue canisters
  • Used along side oxygen
  • Must not exceed 70% of fresh gas flow
  • Less soluble, wears off very quickly
  • Effective analgesic
  • Patient must receive 100% oxygen for 5-10 minutes after turning off to avoid diffusion hypoxia.
159
Q

What is diffusion hypoxia?

A
160
Q

Contraindications for using nitrous oxide

A
  • Will diffuse into and expand gas filled cavities
  • Can expand ET tube cuff
  • Avoid in patients with cardiovascular or respiratory disease
  • Not used in rabbits as gassy hind gut fermenters
161
Q

Second gas effect

A
  • Using nitrous oxide to speed up induction
  • Nitrous has low solubility so moves rapidly from lungs to bloodstream
  • Will take volatile agent during rapid diffusion
  • Will speed induction
162
Q

TIVA

A
  • Injectable IV agents incrementally or constant rate
  • Can only be preservative free propofol
  • Can only be 30 minutes for cats
  • Propofol or alfaxan
163
Q

Disadvantages of TIVA

A
  • Some drugs may accumulate and prolong recovery
  • Difficult to maintain constant depth via incremental
  • CRI requires syringe driver for accuracy
  • -
164
Q

PIVA

A
  • Combining inhalant and IV agent for maintenance
  • Provides very balanced anaesthesia
  • Protocols may be complicated so experiences anaesthetist required
165
Q

Patient positioning under anaesthetc

A
  • Patients in dorsal recumbency may have impaired respiratory function due to pressure on diaphragm
  • Plastic troughs should not be too tight as may interfere with thoracic movement
  • Tying forelimbs tightly may interfere with thoracic movement
  • Patency of airway to ET tube may be compromised especially in ventral recumbency
166
Q

What is pain?

A
  • Sensory and emotional experience
  • Associated with actual or potential tissue damage
  • Caused by noxious stimuli
167
Q

What is a noxious stimulus?

A
  • Damaging to tissues
  • Detected by nociceptors
  • Then activates nociceptive pathways
  • Transmitted by nerves to spine and up to brain
  • Thermal, mechanical or chemical
  • Usually results in pain
168
Q

Nociception is

A

Perception of pain

169
Q

Why is pain detrimental?

A
  • Causes fear, anxiety and distress
  • Delays wound healing
  • Predisposes to intestinal ileus
  • Impairs respiration affecting acid base balance
  • Wound interference and self trauma
  • Prolongs recovery
  • Reduces food intake
  • Affects cardiovascular function due to stimulation of sympathetic nervous system = increased HR and cause vasoconstriction
170
Q

What are the 3 pain catagories?

A
  • Physiological pain
  • Inflammatory pain
  • Neuropathic pain
171
Q

What is physiological pain?

A
  • Early warning device
  • Alert to possibility of tissue damage
  • Pain stops when stimulus stops
172
Q

How can muscle relaxation be achieved?

A
  • Selection of premed agents
  • GA; high concentrations needed, not advised
  • Regional anaesthesia/analgesia
  • Neuromuscular blocking agents (NMBA)
173
Q

What are some indications for use of neuromuscular blocking agents?

A
  • Ocular surgery; prevent downward rotation of eye or unpredictable movements
  • ## Facilitate IPPV; prevent natural override of ventilation
174
Q

What are the 2 types of neuromuscular blocking agents?

A

DEPOLARISING
- Suxamethonium
- Can’t be reversed
NON-DEPOLARISING
- Atracurium, Pancuronium, Necuromium
- Can be topped up without prolonged effect
- Can be reversed

175
Q

What are the functions of anaesthetic breathing systems?

A
  • Transfer gases from GA machine to patient
  • Remove C02 exhaled by the patient
  • Deliver artificial breaths (IPPV)
  • Measure airway pressure, gas volumes and composition
  • Scavenge waste gasses
176
Q

Rebreathing

A
  • Inhalation of previously breathed gases that have taken part in gaseous exchange
177
Q

Reservoir bag

A
  • Open ended or closed bag attached to the breathing system
178
Q

What is IPPV?

A

Intermittent positive pressure ventilation

179
Q

Limbs of circuit

A
  • Tube of breathing system where gases are carried
180
Q

Uni-directional valves

A
  • One way valves
  • Ensure gas only flows in one direction
181
Q

APL valve

A
  • Adjustable pressure limiting valve (Pop off)
  • Controls amount of gas contained within bag and how much escapes through scavenging
  • Usually a plastic disc on spring
  • Depressed when set pressure is exerted to allow gasses to escape
  • Safety system but pressure needed quite high so patient probably have suffered some barotrauma
  • Valve can close and open to control pressure
182
Q

Fresh gas inlet

A
  • Point where gas enters breathing system from common gas outlet on machine
183
Q

Coaxial system

A
  • Inspiratory and expiratory tubes within one another
184
Q

Parallel system

A
  • Inspiratory and exspiratory limbs run side by side
185
Q

Lung compliance

A
  • How well lungs stretch to accommodate a change in volume in relation to pressure applied
186
Q

Circuit resistance

A
  • Pressure drop when breathing through a tube
  • Requires more effort
  • Is increased the longer the tube is
  • Is increased the more turbulent the airflow
  • Smooth bore tubes lower resistance
  • Can be bought for most circuits
  • Smaller patients respiratory function will be effected more by higher resistance due to small tidal volume
187
Q

Mapleson classification

A
  • Way of classifying non rebreathing circuits
188
Q

Advantages of non-rebreathing systems

A
  • Inhalant gas can be adjusted rapidly
  • Minimal circuit resistance
  • Easy to use
  • Cheap to purchase
  • Safe and optimal use of N20
189
Q

Disadvantages of non-rebreathing systems

A
  • High gas flow rates
  • Increase environmental contamination
  • Higher gas and volatile agent costs
  • Potential for rebreathing is tachypnoea leads to insufficient flow rate
  • Heat loss through respiratory tract
190
Q

What measures can be put in place to ensure rebreathing does not occur while using non-rebreathing circuits

A
  • Calculate fresh gas flow rate for every patient
  • Adjust fresh gas flow if RR increases during GA
  • Calculate with correct circuit factor
  • Consider use of capnography
191
Q

Calculating fresh gas flow rates

A
  • Tidal volume = 10-15ml/kg
  • 10ml for over 10kg
  • 15ml for under 10 kg
  • Deep chested may require 12-15mls/kg
  • Minute volume = Tidal volume x RR
  • Fresh gas flow = MV x circuit factor
192
Q

What is the maximum ratio for combination nitrous oxide and oxygen for fresh gas fow?

A

2:1

193
Q

Considerations when selecting a circuit

A
  • Patient weight (choose for lean weight)
  • Will IPPV be needed?
  • Drag on patient from circuit? (pull on tube)
  • Gas flow rate - Higher - hypothermia and costs
194
Q

Ayres T-Piece

A
195
Q

What are rebreathing systems?

A
  • Allows gasses previously exhaled to be reused
  • Use C02 absorbent
196
Q

What are the 2 main rebreathing systems?

A
  • Circle
  • To and fro
197
Q

What are the advantages of rebreathing systems?

A
  • Low gas flow rates; reduce cost and environmental contamination
  • Reduced heat loss by reusing warm air
198
Q

What are the disadvantages of rebreathing systems?

A
  • Altering concentration of VA takes time unless system completely refilled
  • C02 absorbent and valves increase resistance
  • Requires understanding of use
  • Maintenance; C02 absorbent changing
  • Expensive to purchase
199
Q

What is the most common rebreathing system in veterinary industry?

A
  • Circle
  • Models vary; different canisters and tubes
200
Q

What size patient can use a circle system?

A
  • Most suitable for over 10kg
  • Smaller models available
201
Q

What valves do circle systems contain?

A
  • Unidirectional valves
  • (Reubens valves)
202
Q

What are the advantages of the circle system?

A
  • Reduce fresh gas flow/VA costs
  • Less environmental contamination
  • Reduced heat loss from patient
  • Inspired gases moistened
  • Ideal for IPPV
203
Q

What are the disadvantages of the circle system?

A
  • Canisters need refilling; fiddly, hard to clean
  • Canisters can be source of leak; inspect regularly
  • Cost of C02 absorbent
  • Knowledge + time needed for maintenance
  • Will harbour moisture; needs to dry
  • C02 absorbent creates resistance; not suitable for smaller patients
  • Expensive to purchase
  • May exacerbate hyperthermia in large patients
  • Not advised to use nitrous oxide
204
Q

Why shouldn’t nitrous oxide be used with circle circuits?

A
  • Unless experienced anaesthetist with appropriate monitoring equipment
  • Nitrous will accumulate in system
  • Leads to higher concentrations over time
205
Q

How does a circle work?

A
  • At start, period of denitrogenation must take place
  • May be operated as closed/semi closed
  • Contains one way valves to ensure direction
  • Patient breaths in from inspiratory limb
  • One-way valves control exhaled gases
  • Gases flow into reservoir bag
  • Then through soda lime canister
  • Soda lime converts CO2 to O2 to be reused
  • Levels of VA remain same as exhaled from body
  • Small amounts of fresh gas added to system
206
Q

What is denitrogenation?

A
  • Room air contains high levels of nitrogen
  • First anaesthetised, exhale nitrogen
  • If builds up in system, gas mixture hypoxaemic
  • So higher gas flow used for first 15-20 minutes
  • Usually 100ml/kg/min (Open, semi-open)
  • Then gas flow dropped as semi-closed or closed
207
Q

What does a ‘closed system’ mean in reference to circle circuits?

A
  • Supply metabolic oxygen requirement only
  • Operate with valve closed
208
Q

Why are ‘closed systems’ in reference to circle circuits not recommended?

A
  • Metabolic oxygen consumption varies (2-10ml/kg)
  • Flowmeters don’t allow accurate delivery of low flow rates
  • Vaporisers not calibrated for very low flow rates
  • Accurate monitoring to ensure no CO2 rebreathing
  • Reliant on function of CO2 absorbent
209
Q

What is a semi-closed system in reference to circle circuits?

A
  • Operate with valve semi-open
  • 1 litre/min fresh gas flow after denitrogenation
  • Lower FGF rates may be used where adequate CO2 level monitoring in place
210
Q

Why should patients be intubated during anaesthesia?

A
  • Protect airway
  • Maintain patent airway
  • Prevent soft tissue obstruction
  • Prevent secretion obstruction
211
Q

Why are some patients not intubated?

A
  • Depends on size of patient
  • <2kg difficult to tube
  • Small diameter tube cause more resistance
  • Some species can not easily be intubated
212
Q

What are the type of endotracheal tubes?

A
  • Red rubber (Magill)
  • Polyvinyl chloride (PVC)
  • Silicone
  • Cuffed
  • Uncuffed
  • Re-enforced
213
Q

What are the 2 main types of cuffs?

A

HIGH PRESSURE, LOW VOLUME
- More secure protection of airway
- More risk of pressure
LOW PRESSURE, HIGH VOLUME
- Pressure over larger area
- Airway protection not as secure

214
Q

What tubes are usually chosen for dogs?

A
  • Cuffed tubes
215
Q

Why are cuffed tubes not ideal for use in cats?

A
  • Very prone to tracheal necrosis
  • Cuffed only used in high aspiration risk or during ventilation
  • Great care must be taken with cuffed tubes
216
Q

What is an alternative to a cuffed tube when preventing aspiration?

A
  • Throat packs
  • Useful in dentals
217
Q

What are the advantages and disadvantages of red rubber (Magill) tubes?

A

ADVANTAGES
- Re-useable
- Wide range of sizes
- Can be autoclaved
- Easy to intubate as pre-moulded
DISADVANTAGE
- Expensive, especially larger sizes
- Perish with time
- Kink easily
- Cannot see internal contamination
- Cuff valve not self sealing
- Only low volume, high pressure

218
Q

What are the advantages and disadvantages of of PVC tubes?

A

ADVANTAGES
- Cheap
- Designed to be disposable, can reuse
- Malleable when warm
- Fairly kink resistance
- Both low vol, high press + high vol, low press
- Easier to see internal contamination
- Cuffs valved
- Some have murphy’s eye
DISADVANTAGES
- Designed to be disposable
- Cannot be repaired
- Limited sizes - very large unavailable
- Cannot be autoclaved
- Connectors can loosen when tube warms

219
Q

What are the advantages and disadvantages of silicone tubes?

A

ADVANTAGES
- Can be repaired
- Can be autoclaved
- Malleable when warm
- Fairly kink resistant
- Cuffs are valved
- Wide range of sizes
- Can just see internal contamination
- Some have Murphy’s eye
DISADVANTAGES
- Expensive
- May require stylet for intubation as no moulded curve

220
Q

What are the advantages and disadvantages of armoured tubes?

A

ADVANTAGES
- Same as PVC, usually PVC material
- Internal wire coil to prevent kinking
DISADVANTAGES
- Very expensive
- If bitten down on will permanently occlude
- Do not spring back due to wire content

221
Q

Bonus endotracheal tube facts

A
  • Some have radiopaque line
  • Tube size is internal diameter in mm
  • Most tubes have length markings
222
Q

What should be considered when choosing sizes of endotracheal tubes?

A
  • Should be comfortable fit to avoid excessive cuff inflation
  • Tube not too long; bronchial intubation may occur, increased dead space
  • Tubes should not be too short, easily dislodged
  • Measure from front of incisors to thoracic inlet
  • Always get more than one tube size
  • Brachys have very narrow trachea
223
Q

What checks should be done on endotracheal tubes before intubating patients?

A
  • Visually inspect for damage
  • Check lumen clear, pass tube brush, never blow
  • Check cuffs work, inflate, squeeze, fully deflate
224
Q

What are some aids to intubation?

A
  • Laryngoscope
  • Stylets (can use urinary catheter)
  • Silicone based sprays for lubrication
225
Q

What are the types of laryngoscope?

A
  • Miller blade (curved)
  • Macintosh (straight blade)
  • Other specialist blades available for rabbits etc.
226
Q

How are stylets used to intubate patients?

A
  • Stylet placed and threaded over the top
  • Stylet can make tube rigid
  • Urinary catheter can also be used for this
227
Q

How does lube help with intubating?

A
  • Sterile lube
  • Silicone based sprays
  • Reduce trauma
  • If water-based can dry out, become sticky and block tube
228
Q

What is the correct technique when intubating patients?

A
  • Ideally positioned in sternal
  • Head and neck in straight line
  • Cats should have larynx sprayed with local to prevent larangeal spasm - wait 45 seconds
  • Pull out tongue
  • Depress just in front of epiglottis with laryngoscope
  • Pass tube through glottis, into trachea and insert to correct level
  • Secure in place
  • Attach to breathing circuit
  • Give gentle manual breath to listen for leak
  • Slowly inflate cuff until no leak heard
229
Q

How to confirm correct placement of endotracheal tube once placed?

A
  • Ausculate thorax sides to ensure no bronchial intubation
  • Watch for condensation inside tube
  • Check patient chest and bag movement
  • Monitor capnography for CO2 presence
230
Q

How can the cuff be checked to ensure the correct amount of air has inflated it?

A
  • Care to only inflate enough to prevent leakage
  • Checked by listening when patient is given a manual breath
  • More accurate to check pressure cuff is exerting on tissues
  • Special cuff inflator to show pressure
  • Some have automatic shut off
  • Ideal pressure should be 20-30cmH2O
231
Q

What are the different ways gas can be supplied?

A
  • Cylinder
  • Piped gas system
  • Oxygen generator
232
Q

How are piped gas systems run?

A
  • Large cylinders outside of building
  • Small cylinders can attach directly onto anaesthetic machines
233
Q

How is the pressure of oxygen controlled on cylinders?

A
  • Gas runs through pressure reducing valve (regulator)
  • Reduces pressure to safe level
  • Prevents surges
  • Produces consistent pressure
  • Built into machines that use small cylinders
  • Located at source cylinder in piped systems
234
Q

What is the colour code for oxygen cylinders?

A
  • Black cylinder
  • White shoulders
235
Q

What is the colour code for nitrous oxide cylinders?

A
  • Blue
236
Q

How are cylinder sizes identified?

A
  • Letters
  • Later in alphabet, larger the cylinder
  • Portable cylinders often E or F
  • Piped gas systems J or similar
237
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Vet Nurse Small Animal Diploma CQ (14 decks)

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