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RUSVM Anesthesiology > Premedication- A2 Agonist And Phenothiazines > Flashcards

Premedication- A2 Agonist And Phenothiazines Flashcards

1
Q

What are the strongest available sedatives

A

A2 agonists

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2
Q

What is the MOA of a2 agonists and the location of their action?

A

Competitive a2 agonsit

Presynaptic membrane (CNS)

Post synaptic membrane (vascular smooth muscle)

Extra synaptic sites (pancreas / adipocytes)

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3
Q

When activated A2 receptors do what?

A

Inhibit norepi release from the presynaptic membrane

When norepi is released it binds to A2 as a negative feedback

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4
Q

What are the effects of a2?

A

Sedation (brain)
Analgesia (spinal cord and dorsal horn)
Reduction of stress

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5
Q

What is the most concerning side effect of a2 agonists?

A

Vasoconstriction

A2 in wall of arteries along with a1

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6
Q

A2 receptors can be found on adipocytes and pancreatic B cells, what effects will an agonist have concerning these sites?

A

Adipocytes - inhibition of lipolysis

Pancreas - inhibition of insulin release, hyperglycemia

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7
Q

What CNS effects do A2 agonists have?

A

Strong Sedative
Some analgesic effect
Muscle relaxation

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8
Q

What is the most important side effect of A2 agonists ??

A

Strong vasoconstriction

Reflex bradycardia -> low CO and tissue perfusion

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9
Q

What effects do A2 have on respiration

A

Mild depression

RR decrease but tidal volume increase

Upper airway resistance increases
-relaxation of larynx, pharynx and nares

V/Q mismatch

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10
Q

What a2 agonist is contradindicated in sheep and why?

A

Xylazine

  • lung edema and hypoxia
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11
Q

What are the GI effects of a2 agonists

A

Decrease salivation
Lower esophageal sphincter tone decreases
GI motility
Vomiting - cats with xylazine

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12
Q

T/F: Xylazine can cause uterine contractions and abortion in cattle

A

True

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13
Q

When is the use of A2 agonists indicated?

A

Sedation of aggressive animals

Sedation in ICU

Sedation to manage post-op airway obstruction

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14
Q

What are contraindications to A2 agonist use?

A

Too young or too old
Hemodynamic instability
Severely debilitated patient

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15
Q

What is the most selective A2 agonsit used in small animals?

A

Dexmedetomidine

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16
Q

What is the a2 receptor specificity from most to least specific for A2 antagonists?

A

Atipamezole&raquo_space; yohimbine&raquo_space; tolazoline

17
Q

T/F: atipamezole should be used to antagonize any a2 agonist

A

True

Yohimbine and tolazoline are ‘dirty drugs’ acting on other receptors and have many side effects

18
Q

What is the number one choice for a2 agonists in large animals

A

Xylazine

19
Q

T/F: the pre-medication dose for xylazine in horse and cattle is 0.5-1mg/kg

A

False

This is true for horses, but cattle are very sensitive and only require about 10% of this dose

20
Q

T/F: the dose of medetomidine does not differ between horse and cattle

A

True

21
Q

What is the duration of Xylazine ? How does this compare to detomidine

A

Xylazine 20-40min

Detomidine 90-120mins

22
Q

What is the route of admin of detomidine?

A

IM, IV, and sublingual

23
Q

What a2 agonist is used in horses and is thought to produce less ataxia than xylazine, thus is preferred for standing dental surgery

A

Romifidine

Given IM or IV
Duration : 45-90mins

24
Q

What receptors does acepromazine work on?

A

Dopamine
Serotonin
A1
Histamine

-antagonist

25
Q

Is acepromazine short or long acting?

A

Long acting

4-8hrs

26
Q

What effect do phenothiazines have on the CNS?

A

Weaker sedative effects compared to a2 agonist

NO analgesic effect

Antiemetic effect

Mild respiratory depression

27
Q

What effect do phenothiazines have on the CV system ?

A

Antagonist of a1 -> vasodilation and hypotension

*measure BP and give fluids**

28
Q

What are the side effects of phenothiazine?

A

Antihistamine
Anti-arrhythmogenic
Inhibit platelet function

Penile prolapse in horse

29
Q

When is a phenothiazine indicated?

A

Mild sedation for premedication or post op

Prevent opioid dysphoria

Prevent emesis caused by morphine

Sedation for dogs with laryngeal paralysis

Enhance sedative effect of xylazine in horse

30
Q

When is phenothiazines contrainicated?

A

Hypovolemia, hemodynamic instability

Very young or very old

Von-willebrand dz

Boxers may be sensitive(bradycardia)

Breeding stallions (penile prolapse)

31
Q

Butyrophenones have similar sedative effect of acepromazine, how do the side effects differ?

A

Less hypotensive
Stronger antiemetic
Less effect on platelet
Anti arrhythmogenic, not seizureogenic

More likely to cause behavioral side effects

32
Q

What drugs are butyropheones?

A

Droperidol and azaperone

RUSVM Anesthesiology (32 decks)

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