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Flashcards in Sedation and premedication Deck (54):
1

Define premedication

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

2

Aims of premed

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

3

Why are anti-cholinergics used a premeds?

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

4

Major effects - anticholinergics - 5

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

5

2 examples - anti-cholinergics

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

6

Define anxiolytic

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

7

Define sedative

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

8

Define narcosis

drug-induced sleep, not easily aroused

9

Define hypnosis

artificially-induced sleep, broader meaning

10

List the 5 classes of sedatives

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

11

Describe phenothiazines

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

12

Effects - Phenothiazines -8

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

13

List 3 examples of phenothiazines

ACEPROMAZINE (ACP)
PROMETHAZINE
CHLORPROMAZINE

14

Which phenothiazine is the only phenothiazine licensed in animals?

Acepromazine (ACP)

15

When is promethazine used?

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

16

Advantages - acepromazine -3

- 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

17

Disadvantages - acepromazine - 12

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

18

When should you avoid acepromazine?

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

19

Where do BUTYROPHENONES work?

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.

20

When are butyrophenones used?

Pigs, healthy animals
Sedation and behavioue modification

21

Pharmacodynamics - azaperone

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

22

What is the metabolism/excretion of azaperone?

Hepatic metabolism --> inactive metabolites
Renal excretion

23

What class of sedatives does azaperone belong to?

Butyrophenones

24

What can azaperone be combined with?

Ketamine --> immobilisation, anaesthesia
Opioids: for painful diagnostic or minor surgical procedures

25

Define neuroleptoanalgesia

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

26

List 2 examples of neuroleptoanalgesic mixtures

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

27

Are benzodiazepines licensed for vet use in the UK?

No

28

List 3 commonly used benzodiazepines

Diazepam
Midazolam
(Zolazepam)

29

How do benzodiazepines work?

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

30

Main actions - benzodiazepines - 4

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

31

Define anterograde amnesia

= 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

Define retrograde amnesia

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

33

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

True

34

Side effects - benzodiazepines - 4

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

35

Define paradoxical response

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

36

What is Flumazenil an example of?

A benzodiazepine

37

Outline flumazenil action

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

38

List uses of benzodiazepines - 7

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

39

Outline use and administration of diazepam

PO, IV, rectal/intracloacal (IM absorption less predictable)
USE: Appetite stimulation (Cats)

40

List the 2 injectable formulations of diazepam

Propylene glycol and Intralipid (milder)

41

Describe midazolam

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

42

Define tautomer

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

43

Where are alpha-2 receptors found?

located centrally and peripherally. Pre, post and extrasynaptic lcations

44

Pharmacokinetics - alpha2 adrenoceptor agonists

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

45

Effects - alpha 2 agonists

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

What is meant when an animal is 'flat'?

When it is sedated.

47

Side effects - alpha 2 agonists - 8

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

List some examples of alpha2 -adrenoceptor agonists - 5

Xylazine
Detomidine
Romifidine
Medetomidine
Dexmedetomidine

49

Outline xylazine

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

Outline Detomidine

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

51

Outline Romifidine

License -horse
Similar profile as Detomidine
Produces less ataxia

52

Outline medetomidine and dexmedetomidine

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

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

Antagonism using one of the following:
Tolazoline
Yohimbine
Atipamezole
Atipamezole

OVERDOSE MAY CAUSE EXCITEMENT

54

Describe atipamezole

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

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