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CPS > Premedication > Flashcards

Premedication Flashcards

1
Q

What are the aims of premedication?

A
  • Sedation and anxiolysis facilitating handling of the animal
  • Reduction of the stress for the animal
  • Reduction the amount of other anaesthetic agents
  • Provision of a balanced anaesthesia technique
  • Provision of analgesia
  • Counter the effects of other anaesthetic agents to be administered during the anaesthesia procedure e.g. atropine to prevent an opioid mediated bradycardia
  • Contribute to a smooth, quiet recovery after anaesthesia
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2
Q

What are the properties of a good sedative?

A

Reliable sedation and anxiolysis
Have minimal effects on the cardiovascular system
Cause minimal respiratory depression –animals will not be intubated following premedication until induction of anaesthesia, therefore they should breathe spontaneously after premedication
Provide analgesia, e.g. Opioid component
Be reversible: The ability to reverse the effects of premedication may be desirable to hasten recovery from anaesthesia

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3
Q

What type of rugs are medetomidine & dexmedetomidine?

A

Alpha2 Agonists

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4
Q

What Alpha2 Agonists are used in equine and cattle premed?

A

Xylazine, detomidine and romifidine used in horses

Xylazine and detomidine used in cattle

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5
Q

Why do we use medetomidine over xylazine?

A

Xylazine is relatively unselective for the α2 receptor and the agonist effect of xylazine at α1 receptors in the heart is suggested to account for the reduced cardiovascular safety of xylazine compared to dexmedetomidine

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6
Q

Why do we use opioids or benzodiazepines in addition to an alpha 2 agonist in pre-med?

A

Synergism between α2 agonists and opioids or benzodiazepines means that the dose of the alpha 2 can be reduced

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7
Q

Why do we use alpha 2 agonists in pre-med?

A

Alpha 2 agonists provide good analgesia through an agonist effect at spinal cord α2 receptors
The dose of induction and maintenance agents required after alpha 2 agonists are dramatically reduced in small animals

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8
Q

What is the duration an analgesia provided by medetomidine?

A

1hr

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9
Q

Why must A2 agonists be given slowly and to effect?

A

» Alpha 2 agonists produces a biphasic effect on blood pressure (initial increase followed by a return to normal or slightly below normal values)
» Heart rate is decreased throughout the period of α2 agonist administration HR 45-60bpm dogs and 100-120 bpm cats
» Alpha2agonists cause a reduction in cardiac output & in healthy animals. The reduction in cardiac output is not associated with a reduced oxygen delivery to CNS, heart, kidney and brain

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10
Q

Why do A2 agonist pre-meds increase urine output?

A

Urine production is increased due to a reduction in vasopressin and renin secretion- so not for cats with blocked bladders, unless you do a cystocyntesis.

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11
Q

What affect do A2 agonist pre-meds have on glucose in the blood?

A

Endogenous insulin secretion is reduced leading to a transient hyperglycaemia

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12
Q

What affect do A2 agonist pre-meds have on thermoregulation during and post-op?

A

Peripheral vasoconstriction tends to reduce peripheral heat loss so it can be easier to maintain normothermia during the peri-operative period compared to animals given acepromazine

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13
Q

What care should be taken when giving small ruminants A2 agonists pre-med?

A

Small ruminants are quite sensitive to alpha 2 agonists, so they only need a small amount

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14
Q

Can A2 agonist pre-med be reversed?

A

Alpha 2 sedation and analgesia is rapidly reversed by the administration of atipamezole, a specific alpha2 adrenergic receptor antagonist
Reversal is advantageous because the recovery period is noted to be a high risk time for anaesthetic complications

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15
Q

How should atipamezole be administered post-op?

A

IM atipamezole produces smooth and good quality recoveries
IV atipamezole produces a very rapid, excitable recovery from anaesthesia and this route of administration is not recommended

Atipamazole rarely used in horses and cattle

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16
Q

What is the most common Phenothiazine pre-med?

A

Acepromazine commonest/only licensed one

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17
Q

How can sedation be improved with Acepromazine?

A

» With larger doses the duration of action is more prolonged
» The quality and reliability of sedation can be improved by combination with an opioid (neuroleptanalgesia)
» Addition of an opioid also provides analgesia, advantageous since acepromazine itself is not analgesic

» To maximise sedation the animal should be left undisturbed for 30-40 minutes after administration
» Less reliable sedation cf dexmedetomidine

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18
Q

Is Acepromazine an analgesic?

A

No

19
Q

Is ace-romaine reversible?

A

Acepromazine is long lasting & non-reversible so avoid in hypotensive animals

20
Q

Where might the use of acepromazine be a good idea?

A

Acepromazine has anti-arrhythmic properties which may be advantageous during anaesthesia

21
Q

What animals should not have acepromazine?

A

Giant breeds of dog and boxers may be “more sensitive” to the effects of Acepromazine
Do not administer to breeding stallions. Paralysis of the retractor penis muscle has been associated with the use of parenterally administered acepromazine in horses.

22
Q

Why do we not just give benzodiazepines alone?

A

» Benzodiazepines alone produce minimal or no sedation in healthy cats and dogs
» May even cause excitation due to loss of learned “inhibitory” behaviour
» Benzodiazepines are therefore given in combination with other sedatives

23
Q

What are the two main benzodiazepines?

A

Midazolam or diazepam

24
Q

What do we normally combine benzodiazepines with?

A

In dogs benzodiazepines often combined with opioids because both classes of drugs are cardiovascularly stable and the combination can provide reliable sedation

In cats benzodiazepine and opioid is not very sedative, so benzodiazepine is most commonly combined with ketamine

25
Q

In what animals might we use benzodiazepines as part of pre-med?

A

These drugs have minor effects on cardiorespiratory systems
Therefore these drugs tend to be used as premedicants in animals with cardiovascular compromise.
Benzodiazepines are commonly used to manage convulsions, particularly as a first line intervention for animals presenting in status epilepticus

26
Q

What is ASA1?

A

Healthy animal for an elective procedure

27
Q

What is ASA2?

A

• Animal with systemic disease, not exhibiting clinical signs e.g. animal with a grade II heart murmur with no signs of exercise intolerance, change in pulse quality or rate

28
Q

What pre-med will we use for an ASA1 dog?

A

(Dex)medetomidine

29
Q

What pre-med will we use for an ASA2 dog?

A

Acepromazine + Opioid combination
If ASA 2 is not assigned because of a disease that affects cardiovascular system or liver function-can use dexmedetomidine

30
Q

What is ASA3?

A

• Animal with systemic disease causing mild clinical signs, or an animal with a systemic disease that is well stabilized on medication

31
Q

What premed will we use for an ASA3 dog?

A
  • Acepromazine + Opioid (depending on the reason for ASA 3 classification)
  • Will the cardiovascular system will cope with vasodilation induced by acepromazine?
  • Otherwise Benzodiazepine + Opioid
32
Q

What is ASA4?

A

Animal with systemic disease causing clinical signs e.g. a patient with an intestinal foreign body that is causing signs of sepsis

33
Q

What premed will we use for ASA4 dogs?

A

Benzodiazepine + Opioid

34
Q

What is ASA5?

A

Animal that is not expected to survive e.g. a dog presented with a GDV that has severe haemodynamic compromise

35
Q

What pre-med will we use for an ASA5 dog?

A

Low doses of opioids or benzodiazepines prior to anaesthesia
A distinct premedication phase is not usually required in very sick patients

A co-induction technique combining midazolam with either propofol or alfaxalone or ketamine is also helpful

36
Q

What premed will we use in an ASA1 cat?

A
  • The profound sedation caused by dexmedetomidine can be advantageous in cats
  • IV access after light sedation e.g after acepromazine may be difficult to achieve
  • Reversibility
37
Q

What premed will we use in an ASA2 cat?

A
  • Acepromazine + Opioid
  • It may be appropriate to use dexmedetomidine
  • If ASA 2 is not assigned because of a disease that affects cardiovascular system or liver function-can use dexmedetomidine
38
Q

What premed will we use in an ASA3 cat?

A

Acepromazine + Opioid depending on evaluation of the cardiovascular system

Or Benzodiazepine + Ketamine
– Higher doses of ketamine (10 mg/kg IM) will induce anaesthesia
– When sedation / premedication is required a lower dose of ketamine (2.5- 5 mg/kg IM) is usually adequat

39
Q

What premed will we use in an ASA4 cat?

A

Benzodiazepine + Ketamine

Or Opioid alone

40
Q

What premed will we use in an ASA5 cat?

A

Administration of a low dose of a benzodiazepine and opioid around the time of induction of anaesthesia will contribute to a balanced anaesthesia technique
A co-induction technique as described for dogs may also be appropriate

41
Q

Why should we not use Anticholinergics routinely anymore?

A

These drugs have adverse effects too: exacerbate bradycardia before HR increases (atropine), can thicken saliva and cause blockages (cats/ruminants) and can inhibit peristalsis (colic - horses) and bloat in ruminants. These drugs cause mydriasis, corneal drying and bronchodilation. Occasionally they are used for bronchodilation and mydraisis.

42
Q

What is the best route for premed?

A

Choose intramuscular administration of drugs over the subcutaneous route (except maybe rabbits?)

43
Q

How should you dose pre-med?

A

Dose drugs based on lean bodyweight rather than obese weight eg a 40kg Labrador only has the liver of a 20kg Labrador
Reduce drug dose in giant breed dogs to allow for the effects of metabolic body size

CPS (16 decks)

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