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Jorge FCP > premedication > Flashcards

premedication Flashcards

1
Q

What is premedication?

A

the provision of sedation & anxiolysis before induction of anaesthesia

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2
Q

What are the benefits of premedication?

A

Reduction of dose of induction agent
Reduction of dose of maintenance agent
Provide pre-emptive analgesia & preventive analgesia
Ensure a smooth recovery
Prevent side effects associated with other anaesthetic drugs
Premedication/sedation can start at home (anxious/fearful animals)

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2
Q

What is pre-emptive analgesia?

A

the administration of analgesic drugs prior to the onset of noxious stimulation which has the potential to be more efficacious

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3
Q

What is the function of pre-emptive analgesia?

A

Reduced immediate post-op pain
Lowers the intensity and duration of subsequent pain
easier to control with analgesics because the initiation and establishment of peripheral and central sensitisation is potentially reduced

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4
Q

What is multimodal analgesia?

A

combining different analgesics acting by different mechanisms or at different sites in the nervous system

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5
Q

What is the purpose of multimodal analgesia?

A

Additive and improved analgesia
minimises overall side effects by reducing dose of each drug

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6
Q

What is preventive analgesia?

A

combines multimodal and pre-emptive concepts but continues into the early post-operative period

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7
Q

What species is acepromazine (a phenothiazine) used as a premed for?

A

dogs
cats
horses

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8
Q

What is neuroleptanalgesia?

A

a state of sedation and analgesia induced by combining neuroleptic and opioid analgesics

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9
Q

What are the common drugs used to produce neuroleptanalgesia?

A

Phenothiazine agents
a2-adrenoceptor agonists
opioid analgesics

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10
Q

How does acepromazine provide sedation?

A

interferes with dopamine transmission

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11
Q

What are the contraindications of acepromazine?

A

Acepromazine causes a reduction in oxygen delivery to tissues via a reduction in haemoglobin concentration, caused by splenic sequestration of red blood cells therefore, it is not advised to administer acepromazine to patients with anaemia.

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12
Q

Why must acepromazine be used in conjunction with other drugs?

A

does not have antinociceptive or analgesic properties

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13
Q

What are the routes of administration of acepromazine?

A

SC
IM
IV
oral

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14
Q

Give examples of alpha 2 agonists used as premedication in small animals

A

Medetomidine
dexmedetomidine (preferred)

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15
Q

Give examples of alpha 2 agonists used as premedication in horses

A

Xylazine
detomidine
romifidine

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16
Q

Give examples of alpha 2 agonists used as premedication in cattle

A

Xylazine
detomidine

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17
Q

How do alpha 2 agonists cause sedation?

A

Inhibit adenylyl cyclase => reduces levels of cyclic adenosine monophosphate => hyperpolarisation of noradrenergic neurons
As cyclic adenosine monophosphate is inhibited, potassium efflux through calcium-activated channels prevents Ca ions from entering the nerve terminal => suppressed neural firing => inhibit norepinephrine release => reduces activity of ascending noradrenergic pathways => hypnosis and sedation

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18
Q

How do alpha 2 agonists cause analgesia?

A

Stimulation of a-2 receptors in the dorsal horn of the spinal column => inhibits nociceptive neurons and reduces the release of substance P => analgesia

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19
Q

What are the side effects of alpha 2 agonists?

A

profound cardiovascular effects and reduced cardiac output
Increased urine output
miosis (pupil constriction), decreased intraocular pressure and decreased ciliary body perfusion
vomiting

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20
Q

What drug is the antagonist of alpha 2 agonists?

A

atipamezole

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21
Q

Give examples of benzodiazepines used as premeds

A

Midazolam
diazepam
zolazepam
alprazolam

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22
Q

What are the effects of benzodiazepines?

A

anxiolytic (reduces anxiety)
Muscle relaxation
Cardiovascular system stability
No analgesia

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23
Q

What animals should benzodiazepines be used in?

A

ASA 3-5
Not healthy animals (causes excitement)

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24
Q

What is the antagonist of benzodiazepines?

A

flumazenil

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25
Q

What drugs should benzodiazepines be combined with for premedication?

A

opioids
or ketamine
or alfaxalone

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26
Q

What is the drawback of using alfaxalone in large animals?

A

Large volume given IM can be painful

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27
Q

What is the function of opioids in premedication?

A

provide pre-emptive (and preventive) analgesia
synergism with sedatives

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28
Q

Describe the sedative effects of opioids

A

ASA 1+2 - mild sedation when given alone
ASA 3-5 - more profound

29
Q

Give examples of different opioids

A

Butorphanol, buprenorphine (partial agonists - lower analgesic effect)
Methadone, fentanyl, morphine, pethidine (pure agonists)

30
Q

Describe the regulation of opioids

A

Schedule 2 controlled drugs

31
Q

What species can morphine be used in?

A

horse
cat
dog

32
Q

What is the route of administration of morphine?

A

IM
SC
Slow IV

33
Q

What is the duration of effect of morphine?

A

dog - 4hrs
cat - 6-8hrs

34
Q

What receptors does morphine act on?

A

Full MOR agonist

35
Q

What are the side effects/considerations of morphine?

A

Vomiting
Histamine release

36
Q

What are the target species of methadone?

A

horse
cat
dog

37
Q

What are the routes of administration of methadone?

A

IM
SC
Slow IV

38
Q

What is the duration of effect of methadone?

A

~4hrs

39
Q

What type of receptors does methadone act on?

A

Full MOR agonist
NMDA antagonist
NRI (noradrenaline uptake inhibitor)

40
Q

What are the considerations of methadone?

A

high licensed doses

41
Q

What are the target species for pethidine?

A

horse
dog
cat

42
Q

What are the routes of administration of pethidine?

A

IM
SC (Cats)

43
Q

What is the duration of effect of pethidine?

A

1-1.5hrs

44
Q

What type of receptors does pethidine act on?

A

Full MOR agonist

45
Q

What are the side effects of pethidine?

A

histamine release

46
Q

What are the target species for fentanyl?

A

dog
cat

47
Q

What are the routes of administration of fentanyl?

A

IV
IM

48
Q

What is the duration of effect of fentanyl?

A

0.3hrs

49
Q

What type of receptor does fentanyl act on?

A

Full MOR agonist

50
Q

What are the side effects of fentanyl?

A

Decreased HR
Decreased RR

51
Q

What are the target species of butorphanol?

A

horse
dog
cat

52
Q

What are the routes of administration of butorphanol?

A

IM
IV
SC

53
Q

What is the duration of effect of butorphanol?

A

0.75-1hrs

54
Q

What receptors does butorphanol act on?

A

KOR agonist
MOR antagonist

55
Q

What are the relative effects of butorphanol?

A

limited analgesia
Good sedation

56
Q

What are the target species of buprenorphine?

A

horse
cat
dog

57
Q

What are the routes of administration of buprenorphine?

A

IM
IV
SC

58
Q

What is the duration of effect of buprenorphine?

A

6-8hrs
Slow onset

59
Q

What types of receptors does buprenorphine act on?

A

Partial MOR agonist
KOR antagonist

60
Q

Where are opioid receptors found?

A

Throughout the CNS in somatic and visceral sensory neurons (throughout the brain and dorsal horn of the spinal cord) and in the periphery (especially after inflammation)

61
Q

What types of opioid receptors are there?

A

MOR - mu opioid receptors
KOR - kappa opioid receptors
beta-receptors

62
Q

What is the effect of activation of MORs?

A

produces supraspinal and spinal analgesia
euphoria
sedation
miosis (e.g. dogs)
mydriasis (e.g. cats)
respiratory depression
decreased gastrointestinal motility due to inhibition of acetylcholine (ACh).

63
Q

What is the effect of KOR activation?

A

spinal and supraspinal analgesia
mild sedation
dysphoria
diuresis
miosis

64
Q

What is the effect of beta opioid receptor activation?

A

spinal and supraspinal analgesia
cardiovascular depression.

65
Q

Give examples of other drugs possibly given before anaesthesia

A

anticholinergics
antihistamines
H2 receptor antagonists + gastroprotectants (brachy?)
Anti-nausea/vomiting medication and NK1 antagonism
Lidocaine
Steroids or NSAIDs
Antibiotics

66
Q

What premedication should be given to a ASA1 animal?

A

Acepromazine or alpha 2 agonist + opioid

67
Q

Describe premedication of ASA 2 animals

A

Low dose ACP/alpha 2 and opioid usually tolerated
Care with ACP in liver disease
Care with alpha 2 agonists in CVS disease - ACP may be a better option
Alpha 2 agonists may be of use in HCM - hypertrophic cardiomyopathy (low dose)

68
Q

Describe pre-medication of ASA 3-5 animals

A

Avoid the alpha 2 agonists in compromised animals
V low doses of alpha 2 agonist may be used if animal very distressed
Opioid alone may be sufficient to sedate patient (but patients are often quiet/compromised) e.g. methadone or butorphanol
Fentanyl and midazolam (IV) useful
Ketamine and midazolam (IM or IV) cats (not in HCM)
Alfaxalone and opioid is an option (volume of injectate is disadvantage), can add BZD too if necessary

69
Q

Describe the premedication of aggressive patients

A

Alpha 2 agonists alone (even high doses) often insufficient to sedate these animals
Alpha 2 + ketamine + opioid (+/- acepromazine) combination IM

70
Q

What premedication can be given at home for aggressive patients?

A

‘Chill’ protocol (Gabapentin + trazodone or melatonin oral day before and morning of consult, and oral (injectable ACP) or oral transmucosal alpha 2 on arrival)
Alprazolam or diazepam

Jorge FCP (59 decks)

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