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FCP > Anaesthesia and induction > Flashcards

Anaesthesia and induction Flashcards

1
Q

Mode of action: propofol

A
  • Acts on (beta subunit of) GABA receptor
  • This leads to inward direct Cl current hyper polarising the post-synaptic membrane and inhibiting neuronal depolarisation
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2
Q

Characteristics of propofol

A

Milky alkyl phenol

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3
Q

Pharmacokinetics of propofol

A
  • Minimal oral bioavailability means IV route is needed
  • Minimally soluble in water (so is given as an emulsion)
  • Distribution: 98% is protein-bound
  • Metabolism is in the liver via glycoronidation
  • Metabolite elimination is renal
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4
Q

Pharmacodynamics of propofol

i.e. effect on CO, MAP, etc.

A
  • Produces anaesthesia, respiratory depression, decreased CMRO2, depressed cardiovascular reflexes
  • Haemodynamic effects are largely a result of sympathetic depression
    • There is stable CO
    • Decreased heart rate (due to blunted baroreceptor reflex)
    • Decreased MAP, SVR, CVP
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5
Q

Onset of action of propofol

A
  • Rapid uptake by the CNS
  • Induces unconsciousness in 5-8 mins
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6
Q

Effects of propofol

(i.e. broadly: CV effects? Recovery? Analgesia?)

A
  • Respiratory and cardiovascular depression
  • Rapid and smooth recovery
  • No analgesic effects
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7
Q

Suitability of propofol

A
  • Suitable TIVA (top ups or CRI)
  • Can be injected by IV only
  • Consider carefully if the animal already has CV depression
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8
Q

Practical delivery of propofol and common side effects to anticipate

A
  • Titrate to effect
  • Use premed to reduce dose
  • Give slowly over 60s
  • Apnoea is common! Be prepared to rapidly intubate, connect to breathing system and perform IPPV.
  • Repeat doses for several days a week can cause problems in cats (e.g. anorexia, anaemia, unkemptness) because propofol is not being adequately metabolised
    • Cats struggle with phenols
  • Twitching and myoclonus can occur. This can be dramatic and frightening, but is often mild and self-resolving.
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9
Q

Which species is propofol licensed for?

A

Dogs

Cats

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10
Q

Mode of action: alfaxalone

i.e. which receptor

A
  • GABA allosteric modulator (acts on the GABA receptor)
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11
Q

Characteristics of alfaxalone

A

Clear, colourless, neuroactive steroid

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12
Q

Pharmacokinetics of alfaxalone

A
  • Good bioavailability (absorption)
  • Soluble in water
  • Distribution: 30-50% protein bound
  • Metabolised rapidly in liver, also in lungs and kidney
  • Metabolite excretion: mainly renal elimination, small % through bile
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13
Q

Pharmacodynamics of alfaxalone

i.e. effect on HR and others

A
  • Produces anaesthesia
  • Decreased CMRO2
  • Haemodynamic effects are minimal:
    • stable CO
    • stable HR
    • stable MAP, SVR, CVP
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14
Q

Onset of action: alfaxalone

A

Rapid uptake by CNS

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15
Q

Effects of alfaxalone

(Broadly: CV effects? Recovery? Analgesia?)

A
  • Respiratory and cardiovascular depression (probably less than propofol)
  • Recovery rapid and smooth if animal has had premed; if not, can be stormy
  • No analgesic effects
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16
Q

Suitability of alfaxalone

A
  • Suitable for TIVA (CRI or top-ups)
  • Can be given IM for sedation
  • Good for cats, especially if compromised/difficult to secure IV access
17
Q

Practical delivery of alfaxalone

A
  • Titrate to effect: give IV slowly over 60s
  • Reduce required dose by premed; lack of premed can result in agitated recovery
  • Apnoea is much less common than with propofol :)
18
Q

Mode of action: ketamine

A

NMDA receptor antagonist

NMDA receptor is located across the cortex, thalamus, striatum and brainstem

19
Q

Characteristics of ketamine

A

Clear colourless solution with pH 3.5

20
Q

Pharmacokinetics of ketamine

A
  • Good bioavailability
  • Soluble in water
  • 12% protein bound
  • Metabolised in the liver to norketamine (an active metabolite)
  • Eliminated through renal system and a small % in bile
21
Q

Pharmacodynamics of ketamine

i.e. effects on HR etc.

A
  • Dissociative anaesthesia
  • Increased CMRO2
  • Increases cerebral blood flow and ICP
  • Minimal haemodynamic effects:
    • Stable CO
    • Increased HR
    • Increased MAP, SVR, CVP
  • Provides somatic analgesia
22
Q

What is the only analgesic induction agent?

A

Ketamine

23
Q

When would ketamine be contraindicated and when?

A
  • In cases where ICP is a problem
  • Because ketamine increases cerebral blood flow and ICP
24
Q

Onset of action: ketamine

A
  • Rapid uptake by the CNS
  • Induces unconsciousness in 5-8 mins
25
Q

Effects of ketamine

(Broadly: anaesthesia? Analgesia? etc.)

A
  • Produces dissociative anaesthesia
  • Provides somatic analgesia
  • Animals typically exhibit eyes that are wide open and central rather than rotated
  • Poor muscle relaxation, but can be combined with other agents to improve this
    • e.g. horses are given alpha-2 agonist followed by ketamine
    • Can also be combined with benzodiazepines
26
Q

Suitability and usage of ketamine

A
  • Schedule 2 drug: must be kept in a locked cabinet and a record kept of its use
  • Component of the feline triple or quad IM protocols
  • Often used in highly compromised dogs and cats as it increases HR and BP rather than causing CV depression
27
Q

Practical delivery of ketamine

A
  • Can be given IM, IV, or squirted into the mouth of a hissing cat
28
Q

Species licensing: ketamine

A
  • Licensed for cats, cattle, dogs, guinea pigs, hamsters, horses, mice, pigs, rabbits, rats, sheep, sub-human primates
  • Induction agent of choice in horses
  • Used in exotic and lab animals commonly
29
Q

Examples of volatile agents

A

Isoflurane, sevoflurane

30
Q

Pharmacokinetics of volatile agents

A
  • Absorption via the lungs
  • Solubility in tissues/blood varies according to partition coefficient
  • Distribution is via blood to brain
  • Minimal metabolism
  • Elimination is via the lungs
31
Q

Pharmacodynamics of volatile agents

(i.e. effect on HR etc.)

A
  • Produce anaesthesia
  • Cause profound cardiopulmonary depression‼️
  • Whether used for induction or maintenance, only use the absolute minimum.
  • Many problems in anaesthesia arise from overdose:
    • Poor BP → poor perfusion → can be fatal
  • These drugs are basically poisons
    • Reduced CO
    • Reduced HR
    • Decreased MAP, SVR and CVP
32
Q

Onset of action: volatile agents

A
  • Role of lungs causes the drugs to behave differently to injectable agents:
    • IV agents: speed of induction is proportional to cardiac output
    • Inhalants: speed of induction is inversely proportional to cardiac output due to negative effects of high cardiac output on the alveolar partial pressure
    • i.e. if very compromised animal receives inhalant, induction can be v. rapid. If very compromised animal receives IV agent, induction can be v. slow.
      • Reverse is true for recovery.
33
Q

Suitability and usage of volatile agents

A
  • Can be used for induction and maintenance
  • Mask or chamber induction is used whenever IV/IM not possible
  • Beware of stress of restraint/breathing in agent
  • Requires a precision vaporiser to slowly increase % and avoid overdose
34
Q

Species suitability of volatile agents

A
  • Birds
  • Small furries
  • Very compromised animals
35
Q

What should you consider when anaesthetising a brachycephalic animal?

A
  • Have a large selection of ET tubes available
  • Use an induction agent that is not likely to cause apnoea (i.e. alfaxalone rather than propofol)
  • Pre-oxygenation of 100% for 3-5 mins prior to induction
36
Q

CMRO2

A

cerebral metabolic rate

37
Q

SVR

A

systemic vascular resistance

38
Q

CVP

A

central venous pressure

FCP (34 decks)

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