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Principles of anaesthesia > Premedication and sedation > Flashcards

Premedication and sedation Flashcards

1
Q

Goals of pre-medication and sedation

A

To tranquilise the patient

To decrease the doses of anaesthetic agents used for induction and maintenance of anaesthesia

To facilitate a smooth and stress free recovery

Pre-emptive analgesia-good for invasive procedures

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2
Q

Classes of drugs used for premed/sedation

A

Phenothiazines - ACP

Alpha 2 adrenoreceptor agonists - medetomidine, dexmedetomidine, xylazine, romifidine, detomidine

Benzodiazepines - midazolam, diazepam, zolazepam

Opioid analgesics - methadone, butorphanol, buprenorphine

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3
Q

What class of drug is acepromazine (ACP)?

A

Phenothiazine

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4
Q

What class of drugs includes medetomidine, dexmedetomidine, xylazine, romifidine, detomidine?

A

Alpha 2 adrenoreceptor agonists

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5
Q

What class of drugs includes Midazolam, diazepam, zolazepam?

A

Benzodiazepines

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6
Q

What class of drugs includes methadone, morphine, butorphanol, buprenorphine?

A

Opioids

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7
Q

Liccenced premed/sedation drugs for dogs

A

Medetomidine
Dexmedetomidine
Xylazine

Mathadone
Buprenorphine
Butorphanol
Fentanyl

Zolazepam (in Zoletil)

Acepromazine

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8
Q

Liccenced premed/sedation drugs for cats

A

Medetomidine
Dexmedetomidine
Xylazine

Methadone
Buprenorphine
Butorphanol
Fentanyl
(Pethidine)

Zolazepam (in zoletil)

Acepromazine

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9
Q

Liccenced premed/sedation drugs for horses

A

Xylazine
Dexmedetomidine
Romifidine

(Butorphanol)

Acepromazine

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10
Q

Liccenced premed/sedation drugs for cattle

A

Xylazine
(Romifidine)

(Acepromazine)

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11
Q

Liccenced premed/sedation drugs for pigs

A

(Acepromazine)
Azaperone

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12
Q

MoA of Acepromazine

A

Blockade of the dopaminergic receptors D2

Antagonism of the a1 adrenergic receptors

Blockade of histaminic receptors (serotoninergic pathway)

Blockade of the muscarinic receptors

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13
Q

Pros of Acepromazine

A

Long acting tranquiliser (smoother recovery)

Reliable sedation in dogs (aggressive dogs can still wake up and be aggressive)

Some anti-arrhythmic properties (less relevant these days)

Cheap and licensed for many animals (protects against possible legal issues)

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14
Q

Cons of Acepromazine

A

No analgesia (not a big deal if combined with analgesics)

Vasodilation and hypotension (blocks peripheral a1 receptors)

Unreliable in cats

Poorly reliable to sedate aggressive animals

Long lasting effects (up to 6-7 hours)

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15
Q

Which types of patients can Acepromazine be used in?

A

All healthy, young dogs

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16
Q

When should Acepromazine be avoided or used with caution?

A

In cases of:

○ Uncorrected hypovolaemia/hypotension

○ Severe renal disease

○ HCM/ left ventricular hypertrophy

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17
Q

MoA of Alpha-2 adrenoreceptor agonists

A

Stimulation of alpha2 (negative feedback) pre-synaptic adrenergic receptors in the brain and spinal cord, which causes a decrease in noradrenergic activity.

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18
Q

Side effects of Alpha-2 adrenoreceptor agonists

A

Bradyarrhythmia’s (receptors are on the vasculature, the heart etc.)

Stimulation of the alpha1 receptors (vasoconstriction)- could increase blood pressure

More alpha2 selective molecules may cause less vasoconstriction

Central cardiovascular depression owing to decreased adrenergic output (central so bradycardia may not resolve even with vasoconstriction)

Increase in blood glucose levels (stimulation of alpha1 receptors) so need to be careful with diabetes patients but otherwise not too clinically relevant

Respiratory depression

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19
Q

Selectivity of Alpha-2 adrenoreceptor agonists

A

Dexmedetomidine (highest selectivity)

Medetomidine

Romifidine

Detomidine

Xylazine (lowest selectivity)

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20
Q

Pros of Alpha-2 adrenoreceptor agonists

A

Good analgesia (spinal)

Reliable sedation in dogs, cats, and equine

Reliable in a variety of animal species

Antagonizable

Short acting (1 hour)

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21
Q

Cons of Alpha-2 adrenoreceptor agonists

A

Arrhythmogenic

Increase (most common)/decrease in BP

Cardiac and respiratory depression

Moderately expensive (but agent-dependent)

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22
Q

Which patients can Alpha-2 adrenoreceptor agonists be used in?

A

Healthy, young dogs as premedication or to sedate for short ambulatory procedures

Aggressive dogs and cats for IM sedation

Many non-conventional species (rabbits, rats, wild and selvatic animals)

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23
Q

When should you avoid Alpha-2 adrenoreceptor agonists or use them with caution?

A

Severe cardio-respiratory disease/impairment

Diabetic patients

In general, sick animals classified as ASA III

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24
Q

MoA of benzodiazepines

A

Binding of GABAa receptors in the brain and spinal cord, which enhances the effects of GABA (inhibitory neurotransmitter)

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25
Q

Pros of benzodiazepines

A

Cardiovascular and resp functions are minimally affected

Myorelaxation

Tranquilisation in neonates, geriatric, or very sick dogs and cats

Anticonvulsant properties

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26
Q

Cons of benzodiazepines

A

Unreliable as sedative agents in most dogs and cats

Behavioural excitatory reactions are common (might see hallucinations in cats)

Antagonists are expensive

Myorelaxation may result in decrease respiratory function

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27
Q

Which patients can have benzodiazepines?

A

Neonates (less than 4 weeks)

Geriatric or very sick dogs and cats

In patients with increased risk of seizures

In case of severe cardiac impairment

When myorelaxation is desirable (e.g. Fractures)

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28
Q

When should you avoid the use of benzodiazepines, or use them with caution?

A

Healthy young, non-premedicated animals

Hepatic encephalopathy

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29
Q

Which animals do of benzodiazepines have good sedative effects in?

A

○ Pigs
○ Primates
○ Ferrets
○ Rabbits
○ Birds

30
Q

MoA of opioids

A

Action through various ion channels of both pre- and post- synaptic neuronal membranes, which leads to hyperpolarization of the post-synaptic axon and interruption of nociceptive pathways in the brain and spinal cord

Different types of receptors µ, δ and κ

Mimic endogenous opioids

31
Q

Endogenous opioids

A

Endorphins
Dysnorphins
Enkephalins

32
Q

Exogenous opioids

A

Drugs
Powerful analgesic
Treatment of moderate to severe pain

33
Q

Opioid receptors

A

µ: powerful analgesia but also side effect

κ: dysphoria, less potent analgesia

34
Q

Common side effects of opioids

A

Sedation (desired or undesired)

Resp depression

Bradycardia

Dysphoria/excitement

Spontaneous locomotor activity

Changes in pupil size (mydriasis in cats and horses, variable in dogs)

Vomiting

Decreased gut motility

Urinary retention

35
Q

Duration of effects of morphine

A

2-4hrs

36
Q

Is morphine licensed?

A

No

37
Q

Receptoral binding of morphine

A

Potent µ-agonist

38
Q

Special features of morphine use

A

Vomiting and histamine release

39
Q

Duration of effect of methadone

A

Up to 4hr

40
Q

Is methadone licensed?

A

Yes (cats and dogs)

41
Q

Receptoral binding of methadone

A

µ-agonist

42
Q

Special features of methadone use

A

Hyperventilation possible

43
Q

Duration of effect of pethidine

A

1-2hr

44
Q

Is pethidine licensed?

A

Yes - for cats

45
Q

Receptoral binding of pethidine

A

µ-agonist

46
Q

Special features of pethidine use

A

Histamine release (IM!)

47
Q

Duration of effect of fentanyl

A

10-15mins

48
Q

Is fentanyl licensed?

A

Yes (cats and dogs)

49
Q

Receptoral binding of fentanyl

A

Potent µ-agonist

50
Q

Special features of fentanyl use

A

Suitable for CRI

51
Q

Duration of action of butorphanol

A

1-2hr

52
Q

Is butorphanol licensed?

A

Yes (cats and dogs)

53
Q

Receptoral binding of burtorphanol

A

µ- antagonist and κ- agonist

54
Q

Special features of butorphanol use

A

Poor analgesic

55
Q

Duration of action of buprenorphine

A

6-7hrs

56
Q

Is buprenorphine licensed?

A

Yes (cats and dogs)

57
Q

Receptoral binding of buprenorphine

A

Weak µ-agonist

58
Q

Special features of buprenorhine use

A

Useful for post-op analgesia

59
Q

Morphine

A

Gold standard, pure µ-agonist potent opioid

Potential histamine release, vomiting

Duration: 2-4 hours

Not licensed in animals

Schedule 2

60
Q

Methadone

A

Pure µ-agonist opioid

No histamine release if given IV

Duration: up to 4 hours

Licensed for dogs and cats

Schedule 2

61
Q

Butorphanol

A

Κ-agonist and µ-antagonist (mild sedative, poor analgesic)

Used in combination with sedative drugs for minimally invasive procedures

Duration: 1-2 hour

Licensed for dogs and cats

Not listed as controlled drug in the UK

62
Q

Buprenorphine

A

Weak µ-agonist: not as potent as morphine (but better than butorphanol)

Duration: up to 7 hours

Licensed for dogs and cats

Schedule 3 (less controlled than morphine)

Often preferred in practice for its long duration and fewer side effects

63
Q

Pethidine

A

µ-agonist of short duration (1 hour)

Histamine release: must be given IM

Other mechanisms of action (atropine-like, blockade of Na+ channels)

Licensed for cats

Schedule 2

64
Q

Fentanyl

A

Very potent µ-agonist, short acting opioid

Used as an infusion

Licensed for dogs and cats

Schedule 2

65
Q

Naloxone

A

Opioid antagonist - to treat opioid overdose or in crash situation

66
Q

Which patients can opioids be used for?

A

All the patients in pain or undergoing invasive surgeries

As sedatives in patients with cardiac diseases

67
Q

When should opioids be used with caution?

A

Resp impairment (as sedatives)

Allergic conditions, asthma (morphine and pethidine)- can be used but cant be left unattended

68
Q

Sedation/premed protocols

A

Opioid, ACP, benzodiazepine or alpha2-agonist alone

Drugs of the same classes are not combined

Opioid and ACP

Opioid and alpha2-agonist

Opioid and benzodiazepine

69
Q

What does a medetomidine and methadone combination produce?

A

A sleepy dog, happy to be held

70
Q

ACP and methadone combination

A

very good drug combination but take different amounts of time to work, first methadone (A few minutes, little change or more excitement and panting) then acepromazine (after 20mins more sleepy and calm, no panting)

Principles of anaesthesia (9 decks)

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