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CPS > Premedication > Flashcards

Premedication Flashcards

1
Q

List the groups of agents than can be used for premedication

A
  • Alpha 2 agonists
  • Phenothiazines
  • Benzodiazepines
  • Anticholinergics
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2
Q

What alpha-2 agonists are used for premedication in horses?

A
  • Xyalzine
  • Detomidine
  • ROmifidine
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3
Q

What alpha-2 agonists are used for premedication in cats and dogs?

A
  • Medetomidine
  • Dexmedetomodine
  • (replaced xylazine)
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4
Q

What alpha-2 agonists are used for premedication in cattle?

A

Xylazine and detomidine

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5
Q

Compare the use of xylazine and dexmedetomidine

A
  • Xylazine unselective for a2 receptors, and have agonist effect at a1 receptors
  • Reduced cardiovascular safety vs dexmedetomidine
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6
Q

What is the name of the licensed phenothiazine?

A

Acepromazine

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7
Q

Describe the use of acepromazine for premedication

A
  • Used in combination with an opioid for their analgesic effects
  • Called neuroleptanalgesia
  • Leave animal undisturbed for 30-40 mins after administration
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8
Q

Compare the sedation of acepromazine and dexmedetomidine

A

Acepromazine provides less reliable sedation vs dexmedetomidine

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9
Q

Name the benzodiazepines used in premedication

A
  • Midazolam

- Diazepam

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10
Q

Are benzodiazepines licensed for use as predmedication in the UK?

A

No

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11
Q

What are the benefits of benzodiazepines as premedication?

A
  • Used alone produce minimal or no sedation in healthy cats and dogs
  • Better for sick animals
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12
Q

What is a potential effect of benzodiazepines on healthy patients?

A

Excitation due to loss of learned “inhibitory” behaviour

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13
Q

Describe the usage of benzodiazepines for premedication

A
  • Given in combination with other sedatives
  • Often opioids
  • Ketamine in compromised cats
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14
Q

What are the different formulations of benzodiazepines?

A
  • Combined with propylene glycol
  • Water soluble
  • Milky
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15
Q

Why are benzodiazepines commonly given with opioids?

A

Both are cardiovascularly stable and in combination can provide reliable sedation

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16
Q

Name the anticholinergic premedicants

A
  • Atropine

- Glycopyrronium

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17
Q

Describe the use of anticholinergics as premedicants

A
  • Routine premedication with anticholinergics is unnecessary
  • Used in past with irritant inhalants to reduce bronchial secretions and opioids to offset bracycardia
  • Do not use with alpha 2 agonists to offset bradycardia
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18
Q

Describe the mechanism of action of alpha-2 agonists

A
  • Act on a2 and a1 adrenoceptors

- At a2 receptors, bind to presynaptic receptors to have negative feedback on norepinephrine release

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19
Q

Describe the effects of premedication with alpha2 agonists

A
  • Profound sedation (dose related)
  • Synergistic with opioids or benzodiazepines
  • Good analgesia through effects at spinal cord a2 receptors
  • Improved intra-op analgesia
  • Dramatically reduces dose of induction and maintenance agents required
  • Biphasic effect on blood pressure (initial increase, followed by return to normal or slightly below)
  • Heart rate decreased
  • Reduction in cardiac output but not oxygen delivery
  • Minimal effects on respiratory system in healthy animal
  • Increased urine production
  • Peripheral vasoconstriction
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20
Q

Describe the administration of induction agents following alpha-2 agonists as premedication

A
  • IV
  • Must be given slowly to effect
  • Vein to brain circulation time is slowed due to lowered heart rate and cardiac output
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21
Q

Why do alpha2 agonists increase urine production?

A

Reduce vasopressin and renin secretion

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22
Q

How is a2 sedation and analgesia reversed?

A
  • Administration of atipamezole (specific a2 adrenergic receptor antagonist)
  • IM provides smooth recovery
  • IV produces rapid, excitable recovery
  • Ensure analgesia is supplemented with different classes of drugs
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23
Q

Describe the side effects of alpha2 agonists

A
  • Body wide side effects
  • Bradycardia
  • Changes in blood pressure
  • Increased urine production may be dangerous in anuria and distended bladder
  • Mucus membranes blue-grey in colour
  • Endogenous insuline secretion reduced leading to transient hyperglycaemia
  • Liver blood flow and rate of metabolism of other drugs metabolised by liver reduced
  • Small ruminants sensitive to a2 agonists
24
Q

What is the benefit of reversal of alpha2 agonists?

A

Recovery period is noted to be a high risk time for anaesthetic complications

25
Q

Describe the mechanism of action of phenothiazines

A
  • Antagonism of a1 adrenoceptors

- Dopamine antagonist

26
Q

Describe the effects of phenothiazines

A
  • Long lasting and non-reversible
  • Anti-arrhythmic
  • Sedation and anziolysis (dose dependent)
  • Larger doses have prolonged action
  • NO analgesia
27
Q

Describe the side effects of phenothiazines

A
  • Peripheral vasodilation and fall in arterial blood pressure
  • Reduction in body temp due to resetting of thermoregulatory mechanism and vasodilation
  • Giant dogs more sensitive to effects
  • Some boxer dogs very sensitive, low dose recommended
  • Penile priapism in stallions
28
Q

What are the contraindications for phenothiazines?

A
  • Avoid in animals with marked cardiovascular disease, significant haemorrhage or animals in shock
  • Hypotensive animals
  • Breeding stallions
29
Q

How can penile priapism following use of phenothiazines be treated?

A

Compression, slow IV administration of benztropine mesylate

30
Q

What are phenothiazines commonly given in combination with and why?

A
  • Opioids

- Improve quality and reliability of sedation

31
Q

Describe the mechanism of action of benzodiazepines

A

Act on specific receptor site on GABA

32
Q

Describe the effects of premedication with benzodiazepines

A
  • Minor effects on cardiorespiratory system so can be used in animals with CV compromise
  • Commonly used to manage convulsions (esp for animals presenting in status elipticus)
33
Q

Describe the mechanism of action of anticholinergics

A

Parasympatholytics that block acetylcholine

34
Q

Compare atropine and glycopyrronium

A
  • Glycopyrronium does not cross BBB, slower onset

- Less wide eyed side effects vs those seen with atropine

35
Q

Describe the side effects of anticholinergics as premedication

A
  • Exacerbate bradycardia before HR increases
  • Can thicken saliva and cause blockages (cats, ruminants esp.)
  • Inhibit peristalsis (colic in horses)
  • Bloat in ruminants
  • Mydriasis, corneal drying, bronchodilation
36
Q

Describe the routes of administration of alpha-2 agonist premedications

A
  • Injection

- Oral also common in horses

37
Q

What are the routes of administration of phenothiazine premedicants?

A
  • Injection
  • Gel
  • Tablets
38
Q

What are the routes of administration of benzodiazepines?

A
  • Popylene glycol stings, IM administration
  • Water soluble formulations can be IV or IM
  • Milky formulations given IV (does not cause thrombophlebitis)
  • Rectal diazepam in seizures
  • IM diazepam in foals
39
Q

What are the aims of premedication prior to balanced anaesthesia?

A
  • Sedation and anxiolysis facilitating handling of animal
  • Reduction of stress for the animal
  • Reduction in amount of other anaesthetic needed
  • Balanced anaesthesia faciliated
  • Provision of pre-emptive analgesia
  • Counter effects of other anaesthetic agent to be administered during procedure e.g. atropine to prevent opioid mediated bracycardia
  • Contribute to smooth recovery
40
Q

Describe the desirable properties of drugs used for premedication

A
  • Reliable sedation and anxiolysis
  • Minimal effects on CV system
  • Minimal respiratory depression
  • Provide analgesia
  • Be reversible in order to hasten recovery
41
Q

Describe the administration of any pre-medication drug

A
  • Administer premed and allow to take effect, then induce anaesthesia
  • In cats can administer premed and induction agent IM in one syringe
42
Q

What is contained in a “Quad”?

A
  • Ketamine
  • Benzodiazepines
  • Alpha2 agonist
  • Opioid
43
Q

What are some general considerations regarding premedication?

A
  • Combinations depend on status of patient, action of drugs, and purpose
  • Administer premed at time optimal for induction of anaesthesia and surgery
  • IM administration over subcut
  • Dose based on lean bodyweight rather than obese
  • Record dose on chart
  • Reduce dose in giant breed dogs to allow for effects of metabolic body size
44
Q

Outline the factors that affect the choice of premedication

A
  • Reasons for anaesthesia/sedation
  • Duration of sedation required
  • Procedure to be carried out
  • Degree of pain expected from procedure
  • Species and breed of patient
  • Age of patient (lower alpha2agonist dose in geriatrics)
  • Temperament of patient
  • Condition and ASA classification of patient
45
Q

List the common premedications used in dogs and cats

A
  • ACP and opioid
  • A2A and opioid
  • A2A and benzodiazepine
  • A2A with ketamine
  • BZP with ketamine (cats)
  • Opioid with BZP (cats)
  • A2a and BZP and opioid
46
Q

Compare the common premedications used in ASA1 dogs (ACP or dex/medetomidine)

A
  • ACP: less reliable sedation, add opioid, no analgesia, vasodilation and hypertension, minimal respiratory effects, minimal drug sparing effects, not reversible
  • Dex/med: potent sedation, potent analgesia, reduced cardiac output, narroer safety margin, only in normal CV patients, minimal respiratory effect, potent drug sparing effect, reversible
47
Q

Outline the premedication of ASA2 dogs

A
  • ACP and opioid combination most common

- May use dex/medetomidine depending on reason for ASA2 classification

48
Q

Outline the premedication of ASA3 dogs

A
  • ACP and opioid, depending on reason for ASA3 (vasodilation by ACP)
  • Benzodiazepine and opioid (cardiovascular friendly, useful for cardiovascular disease or systemic abnormalities)
49
Q

Outline the premedication of ASA 4 dogs

A
  • Benzodiazepine and opioid

- May use dexmedetomidine post-op to reduce dysphoria, keep sedated with midazolam and methadone

50
Q

Outline the premedication of ASA5 dogs

A
  • Low doses or opioids or benzodiazepines
  • Distinct premedication phase not usually required in very sick patients
  • Co-induction technique combining midazolam with propofol or alfaxalone or ketamine (reduces dose of induction agent, improving cardiovascular stability)
  • For icterus, liver failure, biopsy and euthanasia use fentanyl, and alfaxan for exploratory laparotomy
51
Q

Outline the premedication of ASA1 cats

A
  • Profound sedation by dexmedetomidine can be advantageous
  • IV access after light sedation (may be difficult with ACP)
  • Dex reversible
52
Q

Outline the premedication of ASA2 cats

A
  • ACP and opioid

- May be appropriate to use dexmedetomidine depending on reason for ASA2 classification

53
Q

Outline the premedication of ASA3 cats

A
  • ACP and opioid depending on evaluation of cardiovascular system
  • Benzodiazpine and ketamine (higher dose of ket 10mg/kg IM will induce anaesthesia)
  • When sedation/premedication required, lower dose of ketamine usually adequate
54
Q

Outline the premedication of ASA4 cats

A
  • Benzodiazpine and ketamine
  • Opioid alone (cats with quiet temperament, e.g. buprenorphine, morphine/methadone)
  • Combination of BZP and opioid does not usually result in reliable sedation (very profound)
55
Q

Outline the premedication of ASA5 cats

A
  • Low dose benzodiazepines and opioid around time of induction of anaesthesia contributes to balanced anaesthesia
  • Co-induction as for dogs may also be appropriate

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