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Principles of anaesthesia > Induction of anaesthesia and injectable agents > Flashcards

Induction of anaesthesia and injectable agents Flashcards

1
Q

Stages of anaesthesia

A

I: voluntary movement/excitement - conscious

II: involuntary movement/excitement ‘delerium’

III (light surgical): plane 1
III (moderate surgical): plane 2
III (deep surgical): plane 3
III (excessive surgical): plane 4

IV: paralysis (death followa respiratory and subsequent cardiac paralysis

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2
Q

Changes during anaesthetic induction

A

Reduced jaw tone and palpebral reflex

Loss of righting reflex

Inability to swallow (problem if they vomit etc., but it is required to place an endotracheal tube)

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3
Q

End points of anaesthetic induction

A

Unconsciousness/ hypnosis

Anaesthetic depth adequate to allow endotracheal intubation

Immobilisation/absence of purposeful movement

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4
Q

Order of events in anaesthetic induction

A

IM premed

IV catheter placement

Pre-oxygenation

Anaesthetic agent administration

Endotracheal intubation

Connection to breathing system

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5
Q

Pre-oxygenation

A

Delivery of 100% oxygen for 3-5 minutes prior to anaesthetic induction (flow-by, face mask)

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6
Q

Aim of pre-oxygenation

A

Preparation for post-induction apnoea

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7
Q

Indications for pre-oxygenation

A

Anaesthetic induction (all patients), respiratory disease/airway obstruction, cardiac disease

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8
Q

Disadvantage of pre-oxygenation

A

If not tolerated by animal it may increase their stress level (can happen in cats)

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9
Q

Which agents are used for anaesthetic induction?

A

Injectable: propofol, alfaxalone (two most common)

Inhalational: sevoflurane

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10
Q

Methods of inhalational induction

A

High vaporiser setting and oxygen flow

Via face mask or anaesthetic chamber (high stress for cats and rabbits especially)

Nasal insufflation (foals)

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11
Q

Side effects of inhalational anaesthesia

A

Pungent odour and airway irritation: breath holding, hypoventilation

Stress: arrhythmias

Delayed airway control (induction achieved in 2-5 minutes)

Leakage so everyone in the room will breath some in

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12
Q

Intravenous/intraperitoneal anaesthetic induction agents

A

Tiletamine/zolazepam

Etomidate (only used in patients with severe CV disease, not licensed and v expensive)

Propofol

Ketamine (less popular now for induction)

Alfaxalone

Thiopental (used to be popular but there are ethical issues so not used now)

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13
Q

Intramuscular injectable anaesthetic induction agents

A

Tiletamine/zolazepam

Ketamine

Alfaxalone

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14
Q

Advantages of injectable anaesthetic induction

A

Easy to administer

Basic equipment needed

Less environmental pollution

Improved patient comfort

Better control over anaesthetic depth (IV)

Rapid loss of consciousness/quicker induction process

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15
Q

Disadvantages of injectable anaesthetic induction

A

Cannot be easily reversed once administered

Metabolic/hepatic/renal elimination

Thrombotic potential/thrombophlebitis

IV access required for many molecules

Pain upon injection possible

Carrier substances (preservatives, lipidic emulsions) may cause allergic reactions

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16
Q

Drug class of propofol

A

Phenol

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17
Q

Presentation of propofol

A

Oil-in-water milk coloured lipidic emulsion (pH 7.0-8.5)

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18
Q

Important things to note about propofol

A

Sterility must be maintained (formulation supports bacterial growth)

Not licensed for food producing species

19
Q

MoA of propofol

A

GABAa potentiation (stronger than benzodiazepines)

20
Q

Metabolism of propofol

A

Hepatic and extra-hepatic (plasmatic esterases)

21
Q

Possible contraindication of propofol

A

Pancreatitis

22
Q

Characteristics of propofol induction

A

Quick onset (arm-> brain about 30-90s)

Short duration of effect (5-8mins)

Highly protein bound

Only IV use

23
Q

Dosage of propofol

A

Titrate to effect

Range: 2-6ml/kg

24
Q

Side effects of propofol

A

Respiratory depression

Cardiac depression, vasodilation (arterodilation and venodilation), hypotension

Poor muscle relaxation (excitement/opisthotonos possible)

Pain upon injection

Vomiting/dizziness

25
Q

Propofol and cats

A

Inability to conjugate phenol leads to slower metabolism

Heinz-body anaemia and RBC damage observed after repeated daily injections or prolonged nifusions (>3hr).

Seems safe for induction

26
Q

Drug class of alfaxalone

A

Neurosteroid compound

27
Q

Presentation of alfaxalone

A

Multidose aqeous solution solubilised in cyclodextrin (pH 6.5-7.0)

28
Q

Licensing of alfaxalone

A

Licensed for cats, dogs, pet rabbits, but not food producing species

29
Q

MoA of alfaxalone

A

Potentiation of GABAa

30
Q

Metabolism of alfaxalone

A

Hepatic, but favourable pharmacokinetic profile (no accumulation) non cumulative

31
Q

Characteristics of alfaxalone

A

Quick onset

Short duration of effect: short (5-15 minutes), depending on dose

Relatively low protein-bound

IV or IM use

Technique: titrate to effect (0.5-2 mg/kg)

32
Q

Side effects of alfaxalone

A

Resp depression (dose-dependent)

CV depression, hypotension (myocardial depression, vasodilation), but better preserved baroreceptor reflex.

Poor muscle relaxation/tremors at induction and at recovery (for short anaesthetics)

33
Q

Drug class of ketamine

A

Phencyclidine (e.g. tiletamine)

34
Q

Presentation of ketamine

A

Colourless solution (racemic) with preservative (pH 3.5-5.5)

35
Q

MoA of ketamine

A

Dissociative anaesthesia

36
Q

Metabolism of ketamine

A

Hepatic

37
Q

Characteristics of ketamine

A

Onset of action: up to 60 seconds to reach the brain

Duration of effect: 5-10 min (IV), 10-20 minutes (IM)

Moderate protein binding

Active metabolites (norketamine) excreted by the kidneys (careful use in case of CKD)

IM, IV, intrathecal use (no preservatives!)

Dose range commonly >2-10 mg/kg (depending on species, route, and degree of sedation)

38
Q

Side effects of ketamine

A

Sympathetic stimulation: increased heart rate and blood pressure

Also direct negative inotropic effect

Might increase myocardial oxygen consumption

Increased muscle tone (poor myorelaxation)

Might increase intracranial and intraocular pressures (dose dependent). If you have a patient with a brain tumour and have other options should probably avoid.

39
Q

Etomidate

A

Imidazolic derivative

Not licensed for animals - only under cascade

40
Q

MoA of etomidate

A

Potentiation of GABAa

41
Q

Main advantage of etomidate

A

CV stability is preserved

42
Q

Characteristics of etomidate

A

Quick onset: 20s

Short duration of effect: 6-10 minutes

Intermediate protein-bound

IV use only

Dose range: 0.5-2 mg/kg (titrate to effect)

43
Q

Side effects and disadvantages of etomidate

A

Pain upon injection possible

Primary adrenal suppression: inhibition of plasma cortisol and aldosterone (impaired stress response)

Increased muscle tone, twitched/ tremors possible at induction

Expensive and not licensed

Principles of anaesthesia (9 decks)

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