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Principles of Science BVetMed 3 > Sedation and premedication > Flashcards

Sedation and premedication Flashcards

1
Q

Define premedication

A

Administration of medication prior to anaesthesia:

  • facilitate/improve peri-anaesthetic period
  • long acting drugs may span the whole period
  • animals should be maintained under observation
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2
Q

Aims of premed

A 
Reduce anxiety
Facilitate handling
Peri-operative analgesia
Facilitate smooth anaesthetic induction, maintenance and recovery
Reduce dose (anaesthetics)
Reduce risks of specific complications
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3
Q

Why are anti-cholinergics used a premeds?

A

Less commonly nowadays but to reduce secretions. Also: used when there was:

  • increased vagal tone
  • vagomimetic drugs (opioids)
  • ressuscitation
  • adjuncts to antagonism of mm blockers
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4
Q

Major effects - anticholinergics - 5

A 
Increased HR
Bronchodilation
Decreased secretions (more viscous)
Mydriasis
Reduced GIT motility
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5
Q

2 examples - anti-cholinergics

A

ATROPINE: crosses BBB (remember rabbits have atropine esterase)
GLYCOPYRROLATE: lower magnitude increase in HR (than atropine), longer acting (1 hour), not licensed in animals

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6
Q

Define anxiolytic

A

calming effect, less interest in environment, still aroused by stimuli, AKA tranquilisers/nebulisers (not same but often used interchangeably)

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7
Q

Define sedative

A

calming effect, less responsive to stimuli, sleepiness, may also be analgesics

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8
Q

Define narcosis

A

drug-induced sleep, not easily aroused

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9
Q

Define hypnosis

A

artificially-induced sleep, broader meaning

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10
Q

List the 5 classes of sedatives

A 
Phenothiazines
Butyrophenones
Benzodiazepines
Alpha-2 adrenergic agonists
(opioids?)
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11
Q

Describe phenothiazines

A 
Highly protien bound (>90%)
Lipophilic (cross placenta and BBB)
Hydrophilic (IM absorption)
Hepatic metabolism
Excretion - urine and bile
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12
Q

Effects - Phenothiazines -8

A

CALMING - main reason for use, blocks CNS dopamine-R
POTENTIATE CNS DEPRESSION (of other drugs): opioids, anaesthetics
EXTRAPYRAMIDAL EFFECTS - high doses
PERIPHERAL VASODILATION: blocks alpha-1 adrenergic receptors
ANTI-EMETIC EFFECT: inhibits CRTZ
ANTI-HISTAMINE EFFECTS: blocks H1 receptor
ANTI-MUSCARINIC EFFECTS: antispasmodic in GIT
HYPOTHERMIA: depression of thermoregulatory centre, increased vasodilation –> heat loss

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13
Q

List 3 examples of phenothiazines

A

ACEPROMAZINE (ACP)
PROMETHAZINE
CHLORPROMAZINE

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14
Q

Which phenothiazine is the only phenothiazine licensed in animals?

A

Acepromazine (ACP)

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15
Q

When is promethazine used?

A

ACTIONS:
anti-histamine
For nausea, vomiting, motion sickness (human)

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16
Q

Advantages - acepromazine -3

A
  • Anxiolytic (low dose) OR sedative (higher dose)
  • Anti-arrhythmic: reduce SNS activity, membrane stabilising effects (LA effect), blockade of cardiac alpha adrenergic receptors
  • PO administration - variable absorption
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17
Q

Disadvantages - acepromazine - 12

A

HYPOTENSION - blocks alpha 1 adrenergic receptors, suppresses SNS

SYNCOPE - due to hypotension and bradycardia, brachycephalics more susceptible (naturally high vagal tone and upper airway obstruction)

CARDIAC SPHINCTER RELAXATION: anti-muscarinic effect –> increases risk of reflux and regurgitation

DECREASED PCV and TS - due to splenic sequestration OR vasodilation causing an increased intravascular space volume with consequent RBC dilution

LATE ONSET OF ACTION

LARGER ANIMALS MORE SENSITIVE

CONCOMITANT USE OF ADRENALINE - ACP blocks alpha1 receptors –> vasodilation. Adrenaline may lead to unopposed beta2 activity –> vasodilation.

(SEIZURE THRESHOLD - reduced)

ANTI-THROMBOTIC - due to decreased platelet count, inhibit aggregation, transien

AVOID USE PRIOR TO INTRADERMAL SKIN TESTING

MAY POTENTIATE EFFECTS OF ORGANOPHOSPHATES

RELAXATION OF RETRACTOR PENIS MUSCLE IN HORSES

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18
Q

When should you avoid acepromazine?

A 
Age extremes (BP regulation problems)
Renal/hepatic disease
Hypovolaemia/most shock states
Brachycephalics
Breeding stallions
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19
Q

Where do BUTYROPHENONES work?

A

Same receptors as Phenothiazines - but degree of localisation on specific receptors is variable. They have a sedative action due to dopamine antagonism. Also has anti-emetic properties and causes vasodilation and hypotension.

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20
Q

When are butyrophenones used?

A

Pigs, healthy animals

Sedation and behavioue modification

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21
Q

Pharmacodynamics - azaperone

A

Peak sedation in 15-30 mins (IM)
Sedation duration 2-3 hours
Decrease HR, CO, ABP
Impaired thermoregulation

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22
Q

What is the metabolism/excretion of azaperone?

A

Hepatic metabolism –> inactive metabolites

Renal excretion

23
Q

What class of sedatives does azaperone belong to?

A

Butyrophenones

24
Q

What can azaperone be combined with?

A

Ketamine –> immobilisation, anaesthesia

Opioids: for painful diagnostic or minor surgical procedures

25
Q

Define neuroleptoanalgesia

A

a state of quiescence, altered awareness and analgesia produced by a combination of an opioid analgesic and a neuroleptic

26
Q

List 2 examples of neuroleptoanalgesic mixtures

A

HYPNORM: fluanisone and fentanyl
INNOVAR VET: droperidol and fentanyl
IMMOBILON: acepromzaine and etorphine, extremely potent, immobilisation of large wild animals

27
Q

Are benzodiazepines licensed for vet use in the UK?

A

No

28
Q

List 3 commonly used benzodiazepines

A

Diazepam
Midazolam
(Zolazepam)

29
Q

How do benzodiazepines work?

A

Act of GABA-A receptor: allosteric modulation, increased affinity/active of GABA therefore increased inhibitory NT conductance.

30
Q

Main actions - benzodiazepines - 4

A

Anticonvulsant
Anxiolytic/sedative
Skeletal mm relaxation (minor)
Amnesiac (anterograde)

31
Q

Define anterograde amnesia

A

= loss of the ability to create new memories after the event that caused the amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact.

32
Q

Define retrograde amnesia

A

memories created prior to the event are lost while new memories can still be created

33
Q

T/F: anterograde and retrograde amnesia can occur together in the same patient

A

True

34
Q

Side effects - benzodiazepines - 4

A

Few side effects:
Minimal CVS and resp. depression
Induction of liver enzymes
Possibility of a paradoxical response

35
Q

Define paradoxical response

A

Where a sedative is given and excitement is seen instead of sedation in a small % of animals

36
Q

What is Flumazenil an example of?

A

A benzodiazepine

37
Q

Outline flumazenil action

A

Rapid onset of action (5 mins)
Short elimination 1/2 life - dogs
May facilitate seizures in predisposed animals

38
Q

List uses of benzodiazepines - 7

A

Convulsions/status epilepticus (not HE)
Anxiolytic/sedative
Muscle relaxation (tetanus, urolithiasis)
With opioids (induction, enhance sedation)
With ketamine
Co-induction
Behaviour modifying

39
Q

Outline use and administration of diazepam

A

PO, IV, rectal/intracloacal (IM absorption less predictable)

USE: Appetite stimulation (Cats)

40
Q

List the 2 injectable formulations of diazepam

A

Propylene glycol and Intralipid (milder)

41
Q

Describe midazolam

A

Twice as potent as Diazepam
Shorter acting
PO, IM (water-soluble), IV, intranasal/transmucosal
Metabolites not v active - suitable for infusion

42
Q

Define tautomer

A

they are isomers of a compound which differ only in the position of protons and electrons

43
Q

Where are alpha-2 receptors found?

A

located centrally and peripherally. Pre, post and extrasynaptic lcations

44
Q

Pharmacokinetics - alpha2 adrenoceptor agonists

A

High lipophilicty –> crosses BBB, placenta and MM with ease.
Hepatic metabolism
Renal excretion

45
Q

Effects - alpha 2 agonists

A

SEDATION: duration dose dependent, synergistic with opioids, able to arouse momentarily - caution!, beware stressed patients, CRI
ANAESTHETIC SPARING (50-70%!, IV - slow administration, CRI)
NEUROPROTECTIVE - prevents neuronal death, vasocontriction may help reduce ICP.
ANALGESIA - mostly visceral, some superficial, LA properties (xylazine)

46
Q

What is meant when an animal is ‘flat’?

A

When it is sedated.

47
Q

Side effects - alpha 2 agonists - 8

A

CVS - 3 STAGES: initial HYPERTENSION (peripheral vasconstriction and stimulation of vascular alpha 2 adrenoceptors) –> BRADYCARDIA ( reflex, central sympatholysis,) –> HYPOTENSION. Also makes MM pale or cyanotic. Can be PRO-ARRHYTHMIC

RESPIRATORY: RR reduced, MV maintained, careful of oedema in small ruminants

ENDOCRINE: diuresis due to decreased ADH production and responsiveness, insulin resistance (-> hyperglycaemia), interference with RAAS

GENITO-URINARY: may increased uterine tone, vasoconstriction (placenta)

GIT: reduced mortality and BF, LOS tone reduced –> emesis.

THERMOREGULATION: reduced central heat production, decreased heat loss

HAEMATOLOGICAL: decreased PCV and TS, enhanced platelet aggregation

OPTHALMALOGICAL: decreased IOP

48
Q

List some examples of alpha2 -adrenoceptor agonists - 5

A 
Xylazine
Detomidine
Romifidine
Medetomidine
Dexmedetomidine
49
Q

Outline xylazine

A 
First alpha-2 agonist for vet med
License - dog, cat, horse, cattle
Species sensitivity: ruminants>horse/dog/cat>pig
Causes emesis (cats)
Short half-life
50
Q

Outline Detomidine

A

License - horses, cattle
IV, IM and transmucosal (horse)
Longer action than xylazine

51
Q

Outline Romifidine

A

License -horse
Similar profile as Detomidine
Produces less ataxia

52
Q

Outline medetomidine and dexmedetomidine

A

Medetomidine - 2 isomers - dexmedetomidine is one of them, essentially v similar actions
License - dog, cats but used in many other species
‘Cleaner’ drugs in the group

53
Q

How can you reverse the sedative and CV effects of analgesia?

A 
Antagonism using one of the following:
Tolazoline
Yohimbine
Atipamezole
Atipamezole

OVERDOSE MAY CAUSE EXCITEMENT

54
Q

Describe atipamezole

A

Most selective alpha 2 antagonist available
Most suitable for ‘newer alpha 2 agonists
Cats - more sensitive
Dose adjusted according to time/drugs
Administered IM

Principles of Science BVetMed 3 (110 decks)

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