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Aneasthesia > Premedication > Flashcards

Premedication Flashcards

0
Q

Aims of premed?

A
  • reduce anxiety (stress hormones affect reocvery and healing)
  • facilitate handling
  • contribute to peri-operative analgesia (pre-emptive analgesia, usually opioids)
  • facilitate smooth induction, maintainence and recovery (before anaesthesia fully set in, excitement can be seen)
  • reduce dose of anaesthesic drugs (and hence side effects)
  • reduce risk of specific complications
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1
Q

WHat is premedication?

A

Any medication prior to anaesthesia to facilitate peri-anaesthetic period

  • long acting drugs may span whole period (up to 48hrs post-op)
  • animals should always be maintained under observation
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2
Q

What are anticholenergics used for? Common nowadays?

A
  • counteract secretions (esp airways)
  • usually only when vagus stimulated or vagomimetic drugs (opioids used)
  • resuscitation
    anjuncts to antagonism or muslce blockers
  • used to be used routinely, less common now
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3
Q

Main effects of anticholinergics?

A
  • ^ HR
  • bronchodilation
  • v secretions (watery part, so become more viscous)
  • mydriasis (^ pupil size)
  • v GIT motility
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4
Q

Give 2 common anticholinergics.

A 
Atropine
- crosses BBB so can cause excitement
- rabbit has atropine esterase so can break down 
Glycopyrrolate
- lower magnitiude ^ HR
- longer acting
- NOT LICENSED for use in animals
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5
Q

Define anxiolytics

A
  • calming effects
  • less interest in environment
  • still aroused by stimuli
  • tranquilisers/neuroleptics
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6
Q

Define sedatives

A
  • calming efffect
  • less responsive to sstimuli (pain, loud noise etc.)
  • sleepiness
  • some have analgesic properties (eg. opioids)
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7
Q

Define narcosis

A
  • drug indiced deep sleep

- not easily aroused

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8
Q

Define hypnosis

A

Artificially induced sleep

  • broader term
  • eg. rubbing chickens on the neck
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9
Q

5 main classes of sedatives ?

A
  • Phenothiazines
  • Butyrophenones
  • Benzodiazepines
  • a2 adrenergic agonists
  • opioids (?)
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10
Q

Phenothiazines - drug properties and impacts clinically? How are they excreted?

A
  • highly protein bound (so if hypoproteinaemic will have less protein bound drug circulating)
  • lipophilic (cross palcenta and BBB)
  • hydrophilic (IM absorption good)
  • hepatic metabolism (may last longer if liver or kidney function impaired)
  • excretion via urine and bile
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11
Q

How do phenothiazines cause calming effect?

A
  • blockade of DA-Rs in CNS
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12
Q

What effects do phenothiazines potentiate?

A

CNS depressant effects of other drugs

  • opioids
  • anaesthetics
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13
Q

What side effects may phenothiazines have at high doses?

A 
> Extra-pyramidal effects 
- fine motorr control impaired
- ataxia
- restlessness
(annoying, not serious) 
> Peripheral vasodilation
- blockade of a1 Rs
> anti-emetic
- inhibition in CTZ of DA, H1, Ach 
> Anti-histaminic effects 
- H1-R blockade
> Anti-muscarinic effects
- anti-spasmodic in GIT
 >Hypothermia
- depression of thermoreg centre
- vasodilation
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14
Q

What is the most common and only licensed phenothiazine in UK? Other potential drugs?

A

> Acepromazine most common

  • Promethazine (Phenergan) mainly used for anti-nausea in humans
  • Chlorpromaine (Largactil) mainly used as anti-psychotic in humans
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15
Q

Good aspects of ACP? (Acepromazine)

A
  • Anxiolytic at low dose, Sedative at high dose
    > Long duration of action
  • anti-arrythmic (reduce activity SNS, membrane stabilising properties -> local anaesthetic effect, blockage cardiac a adrenoceptors. Less important now but useful esp. in horses
  • may be absorbed PO (varibale absorption)
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16
Q

Down-sides to ACP

A
  • hypotension (suppressing SNS< blockade of a1Rs)
  • syncope (esp. brachycephalyic breeds, due to hypotension and bradycardia)
  • relaxation of cardiac sphicter -> regurgitation and reflux
  • decreased PCV and TS (dogs, cows and horses demonstrated, due to vasodilation or splenic sequestration?)
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17
Q

Annoying aspects of ACP?

A
  • late duration of action (wait 30mins even IV)
  • larger animals more sensitive (dose body surface area rather than weight?)
  • concomitant use with adrenaline can cause vasodilation (ACP blocks a1-Rs (-> vasodilation) low dose adrenaline may lead to unoppoosed b2 activity -> further vasdiltion
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18
Q

How MAY ACP affect seizures?

A

POtentially lowers seizure theshold but propbably not - severala papers show otherwise

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19
Q

How may ACP affect thrombosis?

A
  • decreased platelet count

- poor coagulation transiently only

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20
Q

What test should ACP not be used prior to?

A

intra-dermal skin tests

- anti-histamine effects

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21
Q

What drugs may ACP potentiate the action of ? How?

A

Organophosphates

  • reversible inhibition of acetylcholinesterases
  • beware recent ectoparasiticides
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22
Q

How may ACP cause problems in breeding animals?

A
  • relaxation of retractor penis m
  • mainly stallions, also geldings
  • priapism reported
  • may result in trauma/paraphimosis
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23
Q

Which animals should ACP not be given to?

A
  • extremes of age
  • renal/hepatic disease
  • hypovolameia (except cardiogenic shock as may be helpful here)
  • brachycephalic breeds
  • breeding stallions
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24
Q

Which receptors do butyrophenones act on? What are their actions?

A
  • mostly same as phenothiazines
  • dopamine antagonism -> sedation
  • antiemetic
  • vasodilation and hypotension
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25
Q

What is the one butyrophenone licensed in the UK? What is it licensed for?

A

Azaperone

  • healthy animals only
  • sedation and behaviour modification (aggression control when mixing new pigs_)
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26
Q

Pharmacodynamics of azaperones?

A
  • peak sedation 15-30ins IM

- Duration of action 2-3hrs

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27
Q

Physiological effects of azaperone?

A
  • v HR, CO, ABP

- impaired thermoregulation (mild effects if used alone)

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28
Q

Brand name of azaperone?

A

Stresnil

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29
Q

What is Azaperone likely combined with?

A
  • ketamine for anaesthesia or immobilisation

- opioids for painful diagnosics/minor surgical procedures

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30
Q

How is azaperone metabolised and excreted?

A
  • Hepatic metabolism to inactive metabolites

- Renal excretion

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31
Q

What are neuroleptoanalgesics? Which is the only one licensed in the UK? For which species?

A
  • combination of anxiolytic and analgesic (Hypnorm, Innovar Vet [droperidol and fentanyl, USA license = hypnorm], Immobilon [ACP and etorphine, extremely potent, used for large wild animals])
    > Hypnorm (fluanisone and fentanyl)
    > licensed UK for..
  • mice, rats, rabbits and guinae pigs
  • diagnostics and minor surgery or major surgery with BDZs
32
Q

Are benzodiazepines licensed in the UK? Are they used commonly?

A
  • None licensed for vet use

- Used very commonly

33
Q

Most commonly used benzodiazepines?

A
  • Diazepam
  • Midazolam
  • (Zolazepam may be seen some places)
34
Q

How do benzodiazepines work?

A
  • potentiate effects of GABAa (inhibit CNS activity)
    > allosteric modulation
    > increase affinity and action of GABA (Inhibitory NT that ^ Cl conductance)
  • only works in presence of GABA
35
Q

Main actions of bezodiazepines?

A
  • anxiolytic
  • anticonvulsant
  • skeletal muscle relaxation
  • anterograde amnesic
36
Q

Side effects of Benzodiazipines?

A
  • minimal CV and resp depression (mainly with other drugs exacerbated)
  • induction of liver enzymes (may ^ metabolism of other drugs)
  • possibility of paradoxical excitement (combine with something else to mitigate potential for this?)
37
Q

What is the most common benzodiazepine ANTAGONIST used? Onset of action and elimination half life?

A

Flumazenil

  • quick onset of action (5mins)
  • short elimination t1/2 (1 hr in dogs) so unwanted signs of initial sedative may return
  • may facilitate seizures in predisposed animals
38
Q

Uses of benzodiazepines?

A 
> convulsions/status epilepticus 
- not with hepatic encepalopathy 
> axiolytic/sedative
> muscle relaxation 
- tetanus
- urolithiasis (skeletal m. in uretrha) 
> with opioids for induction or enhanced sedation in anaesthesia 
> to counteract ketamine effects of muscle rigidity 
> behaviour modification
39
Q

How can diazepam be administered?

A
  • PO, IV, rectal/intracloacal

- IM maybe, poor absorption

40
Q

What side effect can diazepam have in cats? Is this common?

A

Fulminant hepatic failure if given PO

- rare

41
Q

What is another efect of diazepam in cats?

A

Appetite stimulant very effective

42
Q

What are the 2 injectable forumlations of diazepam?

A

> Valium: Propylene glycol solvent (can cause pain on injection and haemolysis)
Diazemuls: Intralipid (milder formulation)

43
Q

What are the metabolites of diazepam like?

A

Active so shouldn’t be given as a CRI

44
Q

How does midazolam compare to diazepam in potency, time of action and administration routes?

A
  • 2x as potent
  • shorter acting
  • PO, IM, IV, intranasal/transmucosal
  • water soluble so doesnt have same problems with IM injection as diazepam
45
Q

How do the metabolites of midazolam compare to diazepam?

A

not as active so can be given as a CRI

46
Q

Egs. of a2-adrenoceptor agonists?

A
  • xylazine
  • detomidine
  • romifidine
  • medetomidine
  • dexmedetomidine
47
Q

Where are a2 adrenoceptors located? What are the actions of a2 agonists?

A

Everywhere! Pre, post and extra synaptically
- central and peripheral
> Pre-synaptic DECREASE the release of norepinephrine and v SNS activity

48
Q

Pharmacodynamics of a2 ags? Efffects of this?

A

> high lipophylicity

  • cross BBB (good)
  • cross placenta (can be bad)
  • cross mucous membrances (if squirted in eye can affect vet!)
49
Q

Where are a2 ags metabolised and excreted?

A

Metabolised inthe liver excreted by the kidney

50
Q

Effects of a2 ags

A
  • Sedation
  • dose dependant DURATION
  • synergistic with opioids
51
Q

What is a down side to a2 ags sedation?

A
  • Able to rouse momentarily (if aggressive can come round and bite if stimulated)
  • Very stressed patients may not work on until they calm down
52
Q

Can a2 ags be given as a CRI?

A

Yes

53
Q

How do a2 ags interact with anaesthetics?

A

> anaesthetic sparing

  • IV agents should be given at lower doses as v HR caused by a2 ags mean it takes a lot longer for drug to distribute around the body
  • 50-70% sparing
  • can give as CRI
54
Q

How may a2 ags affect the brain?

A

May be neuroprotective (not proven)

  • reduce neuronal death by causing vasoconstriction and reducing ICP
  • except for in DISEASED areas of brain - this can be useful, termed robin hood effect - allows vasodilation in diseased areas only thus ^ healing
55
Q

Do as ags provide analgesia?

A

Yes

  • mostly visceral, some superficial
  • some have local anaesthetic properties (xyalzine if given as an epidural)
56
Q

Side effects of a2 ags in CV system? How is this seen clinically?

A
  • initial hypertension (vasoconstriction, stimulation of vascular a2 adrenoceptors)
  • reflex bradycardia (vagally mediated) Sympatholysis
  • hypotension potentially due to v NAdr release
    > Pale/cyanotic mms
    > Pro-arrythmic: bradyarrythmias and AV block
57
Q

Side effects of a2 agonists in respiratory system?

A
  • RR reduced, TV increased = minute volume maintained, no effects
  • small ruminants (esp sheep)pulmonary resistance ^ -> pulmonary oedema formation and hypoxaemia
58
Q

Side effects of a2 agonists in endocrine system?

A

> Diuresis due to v production and responsiveness of ADH
Insulin resistance -> hyperglycaemia
- Interference with RAAS

59
Q

How do a2 ags affect the genito-urinary system?

A
  • ^ uterine tone (can cause abortion) demonstrated in sheep
  • vasoconstriction may affect o2 delivery to foetus
  • can cross placenta
60
Q

How do a2 agonists affect GIT?

A
  • v motility and blood flow
  • LOS tone reduced
  • possible emesis esp. cats
61
Q

How do a2 ags affect thermoregulation?

A
  • central v heat production

- decreased heat loss? (look up)

62
Q

How do a2 ags affect haematological parameters?

A
  • v PCV and TS

- enhanced platelet aggregation?

63
Q

How can a2 ags affect the eyes?

A
  • v intraocular pressure
64
Q

Which species if xylazine licensed for use in? How does species senstivity differ?

A

Dog, cat, horse, cattle
Sensitivity:
Ruminants > Horse/Dog/Cat > Pig

65
Q

What effect does xylazine commonly have on cats?

A

EMesis

66
Q

What is the t1/2 of xylazine like?

A

Short

67
Q

WHich species is detomidine licensed for use in? ROA? (routes of administration)

A

Horse and cattle

- IV, IM and transmucosal in the horse

68
Q

How does t1/2 of detomidine compare to xylazine?

A

longer action than xylazine

69
Q

Which species is romifidine licensed for use in?

A

horses

70
Q

How do the effects of romifidine compare to other a2 agonists?

A

Similar profile to detomidine

- produces less ataxia

71
Q

What are medetomidine and dexmedetomidine?

A

Isomers of each other - one is active

72
Q

Which species are medetomidine and dexmedetomidine licensed for use in?

A

Dogs and cats but used in many species

73
Q

How is dexmed dosed in dogs?

A

to BSA not weight

74
Q

What drugs can be used to antagonise a2 ags? What may overdose of these drugs cause?

A
  • tolazoline
  • yohimbine
  • atipamezole
    > overdose = excitement
75
Q

Which is the most selective a2 antagonist (ie. a2 ag antagonist) available? ROA?

A

Atipamizole given IM

76
Q

Which species are more senstitve to atipamizole?

A

cats

77
Q

Which drugs is atipamizole most suitable for?

A

Newer a2 agonists

78
Q

What are the main differences between different a2 agonists?

A

Selectivity for a2 receptor resulting in different levels of side effect

Aneasthesia (11 decks)

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