Sedatives and Anesthetics Part 1 Flashcards
(48 cards)
Name the alpha 2 drugs?
- Dexmedetomidine
- Medetomidine
- Xylazine
- Yohimbine
Alpha 2 effects on nociception?
Perception, Modulation, and Transmission
Describe some general info on alpha 2 agonist receptors?
- Brain & spinal cord
- Vascular endothelium
- Endocrine organs
↓ Insulin
↓ Renin
↓ NE release
↓ Pancreatic secretion
Which alpha 2 agonist do we use for Dogs, cats, exotics?
Dexmedetomadine
Which alpha 2 agonist do we use for horses, deer, and elk?
Xylazine
Name the alpha 2 antagonists and which alpha 2 drug they antagonize?
Atipamezole (antagonizes dexmedetomidine)
Yohimbine (antagonizes xylazine)
Name the alpha 2 agonists?
Dexmedetomidine
Xylazine
Name the mechanism of action for sedative and analgesic effects?
Competitive agonism of the alpha 2 receptors (located in the brain/spinal cord)
Name the mechanism of action for ANS effects?
Competitive agonism of α1-receptors (vasculature–> vasoconstriction)
Varying degrees of α1-adrenergic receptor agonism can cause these two reactions?
Paradoxical CNS excitement
Peripheral vasoconstriction
Out of the alpha 2 drugs who is most selective and who is least selective?
- Dexmedetomidine
2. Xylazine
Most common routes of adm.?
IV or IM are the most common routes of administration
- Also can be given as a CRI and epidurally
- Oral transmucosal administration
Do they cross the BBB?
yes! Widely distributed to all tissues
Describe the onset and duration of action of Xylazine? What about Medetomidine and detomidine?
Xylazine onset of action is rapid within min IV
-15 minutes IM)
Duration of sedation ~1–2 hr
Analgesia ~15 to 30 min recovery up to 4 hr
Medetomidine & detomidine slightly longer
Describe the metabolism and elimination?
Rapid hepatic metabolism (short T1/2) followed by urinary excretion
Alpha 2 agonism main effects in the CNS?
- Sedation (alpha 2 receptors in the brain, CNS excitation in large doses)
- Pain Modulation and Analgesia (α2 receptors in brain and spinal cord)
- Muscle relaxation (spinal cord interneurons)
- Emesis (Stimulation of α2 receptors in the emetic center & CRTZ)
What is the drug of choice for emetic effects in cats?
Xylazine
What is unique about their cardiovascular effect? Name the phases
It’s a BIPHASIC Effect
Phase I – Peripheral Phase
Phase II – Central Phase
Describe the Phase 1 - Peripheral Phase
- Mediated by α1 receptors
- Peripheral vasoconstriction (↑ systemic vascular resistance (SVR) causes transient ↑ in mean arterial blood pressure (MAP) causes reflex bradycardia
- HR drops to maintain constant cerebral perfusion pressure (CPP)
if anticholinergics are given at this time they will force the heart to beat faster against the high SVR
Contraindicated - will cause ↑ myocardial workload and oxygen demand, can exacerbate pre-existing heart disease, can cause or worsen arrhythmias
Describe Phase II – Central Phase?
Mediated by α2 receptors
Decreased sympathetic tone (↓ NE) heart rate stays low
↓ Dronotropy (rate of conduction) & ↓ SA node firing
Peripheral vasodilation due to central effects on vasomotor center + low catecholamine levels
Often results in hypotension and bradycardia
Cardiac output can decrease 30-50% with α2 - agonists
Summary of the Cardiovascular effects?
↓ Cardiac output due to ↑ BP and reflex bradycardia
Bi-phasic effect due to initial vasoconstriction and hypertension followed by vasodilation and hypotension due to CNS depression
Bradyarrhythmias (incomplete AV block (2◦ most common)
Myocardial depression
Sensitizes myocardium to catecholamines tachyarrhythmias also possible
All effects are reversible
Alpha 2 agonist other effects respiratory effects?
Centrally mediated decrease in respiratory rate
Mild respiratory depression compared to other drugs
Cats may be more sensitive
Sheep and goats and horses
Increased respiratory rate, airway pressures (resistance) and; pulmonary elastance
Activation of pulmonary macrophages
Leading to ↑ CO2, hypoxemia, pulmonary edema
Also seen in unborn, near term lambs (these drugs cross the placenta!)
What do they do to the GI?
↓ GI motility (esp. large intestine)
↓ acid secretion
