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Anaesthesia > Sedation and Premedication > Flashcards

Sedation and Premedication Flashcards

1
Q

What is premedication?

A

Administration of medication prior to anaesthesia, giving sedative and analgesic effects

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2
Q

What are the aims of premedication?

A 
Reduce anxiety
Facilitate handling
Contribute to peri-operative analgesia
Facilitate smooth anaesthetic induction
Reduce the dose of anaesthetic agent
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3
Q

What are anticholinergics used for in anaesthesia?

A

Mimicking action of efferent fibres of the vagus nerve

  • Increase vagal tone (e.g. to counteract bradycardia)
  • Vagomimetic drugs (opioids)
  • Ressuscitation (atropine)
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4
Q

What are the major effects of anticholinergics?

A 
Increase HR
Bronchodilation
Decrease secretions
Mydriasis
Reduced GI motility
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5
Q

In what animals would glycopyrrolate be a better choice that atropine?

A

Animals where you do not want any central effects and pregnant animals - does not cross the BBB.

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6
Q

How do anticholinergic agents act?

A

They block the neurotransmitter acetylcholine in the central and peripheral nervous system.

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7
Q

What are the three categories of anticholinergics?

A

Antimuscarinic agents
Ganglionic blockers
Neuromuscular blockers

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8
Q

What can anticholinergic drugs be used to treat?

A 
GI disorders
Genitourinary disorders
Resp disorders
Sinus bradycardia
Insomnia
Dizziness
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9
Q

What does anxiolytic mean?

A

A medication that inhibits anxiety

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10
Q

What is a sedative?

A

A substance that induces sedation by reducing irritability or excitement

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11
Q

Define narcosis

A

A state of stupor, drowsiness or unconsciousness produced by drugs

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12
Q

What are the classes of sedatives?

A 
Phenothiazines
Butyrophenones
Benzodiazepines
Alpha 2 agonsts
Opioids
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13
Q

Describe the physiological properties of phenothiazines

A

Highly protein bound (90%>)
+ so must consider hypoproteinemia and hypoalbuminaemia
+ animals with GI problems may be absorbing proteins insufficiently or have excessive renal excretion
+ increased free drug&raquo_space; increased drug action

Lipophilic (cross placenta and BBB)

Hydrophilic (IM absorption)

Hepatic metabolism

Excretion via urinae and bile

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14
Q

What is the main reason for use of phenothiazines? How is it brought about?

A

Calming effect via blockage of dopamine receptors in the CNS

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15
Q

What are the effects of phenothiazines?

A

Peripheral vasodilation
Blockage of alpha1 receptors

Anti-emetic effect
Inhibition in the CTRZ

Anti-histamine effects
H1 receptor blockade

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16
Q

Which phenothiazine is licensed for use in animals?

A

Acepromazine

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17
Q

What are the positive properties of ACP?

A

Anxiolytic at low doses, sedative at high doses

Anti-arrhythmic effects

May be administered orally

18
Q

What are the negative properties of ACP?

A

Hypotension

Bradycardia

Relaxation of cardiac sphincter

Decrease in PCV and TS

Late onset (30 mins)

Larger animals more sensitive

Concomitant use with adrenaline

Lowers the seizure threshold

Antithrombotic

Relaxation of retractor penis muscle in horses

19
Q

How does ACP lead to hypotension?

A

Blockade of alpha1 adrenergic receptors leading to vasodilation

20
Q

Why might ACP be contraindicated in brachycephalics?

A

More susceptible because they have higher vagal tone.

Causes relaxation of the laryngeal muscles and thus upper airway obstruction

21
Q

Why might ACP be contraindicated in stallions?

A

Relaxation of retractor penis muscle in horses
mainly stallions but also in geldings

Priapism (persistent and painful erection of the penis) is also reported

Can result in trauma or paraphimosis (an uncommon medical condition in which the foreskin becomes trapped behind the glans penis, and cannot be reduced)

22
Q

In which animals should you avoid the use of ACP?

A 
Extemes of age
Renal or hepatic disease
Hypovolaemia and/or most shock states
Brachycephalic breeds (Boxer?)
Breeding stallions
23
Q

What are the properties of butyrophenones?

A

Mostly acts on the same receptors as phenothiazines

Sedative action by dopamine antagonisms

Antiemetic properties

Vasodilation and hypotension

24
Q

Describe the pharmacodynamics of azaperone…

A

Peak sedation 15-30mins if IM

Duration of action 2-3 hours

Decrease in HR, CO and ABP

Impaired thermoregulation

25
Q

What animals is azaperone used in?

A

Healthy pigs

26
Q

What benzodiazepines are commonly used in anaesthesia?

A

Diazepam

Midazolam

27
Q

How do benzodiazepines work?

A

Act on the GABA receptor to increase affinity and action of GABA as an inhibitory neurotransmitter

28
Q

What are the main clinical actions of benzodiazepines and their side effects?

A

Main actions

  • Anticonvulsants
  • Anxiolytics or sedative
  • Skeletal muscle relaxation
  • Amnesiac

SEs:

  • Minimal CVRS depression
  • Induction of liver enzymes
  • Possiblity of paradoxical actions
29
Q

What can be used to antagonise benzodiazepines?

A

Flumazenil

30
Q

What are the uses of benzodiazepines?

A

Convulsion for status epilepticus

Anaesthesia

  • Muscle relaxation
  • Induction with ketamine or opioids
31
Q

What are the positive properties of using alpha 2 agonists in anaesthesia?

A

Sedation

Anaesthesic sparing

Neuroprotective

Analgesia

32
Q

What are the side effects of using alpha 2 agonists in anaesthesia?

A

Initial hypertension via vasoconstriction of alpha 2 receptors in peripheral vasculature

Bradycardia as vagal mediated reflex

RR reduced

Diuresis due to reduced ADH production

33
Q

List a range of α2-adrenoceptor agonists.

A 
Xylazine
Detomidine
Romifidine
Medetomidine
Dexmedetomidine
34
Q

Describe the species sensitivity of xylazine…

A

Ruminants > horse/dog/cat > Pig

35
Q

What drug antagonises alpha 2 agonists?

A

Atipamezole

36
Q

What are the effect of alpha-2 agonists on thermoregulation, haematology and opthalmology

A

Thermoregulation:
Reduction in heat production (central)
Decreased heat loss?

Haematology:
Decreased PCV and TS
Enhanced platelet aggregation?

Opthalmological
Decreased intraocular pressure

37
Q

What are the genito-urinary effects of alpha-2 agonists

A

May increase uterine tone -> abortion
Vasoconstriction may affect O2 delivery to foetus
Able to cross placenta

38
Q

What are the GIT effects of alpha-2 agonists

A

Reduced motility and blood flow

Lower oesophageal sphincter tone reduced - may cause reflux

Possible emesis

39
Q

What are the endocrine effects of alpha-2 agonists

A

Diuresis
Reduced ADH production and responsiveness

Insulin resistance - hyperglycaemia

Inferference w/ RAA axis

40
Q

Two ways in which phenothiazines can cause hypothermia

A

Depression of the thermoregulatory centre

Increased heat loss (vasodilation)

Anaesthesia (9 decks)

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