Premedication Flashcards
What does premedication affect?
The characteristics of the ensuing anaesthetic.
Describe the 7 aims of premedication.
- Sedation and anxiolysis (inhibits anxiety) - faciliates animal handling
- Reduction of stress for the animal
- Reduction of the amount of other anaesthetic agents
- Provision of a balanced anaesthetic technique
- Provision of analgesia
- Counter the effects of other anaesthetic agents to be administered during the anaesthesia produced e.g. atropine to prevent an opioid mediated bradycardia
- Contribute to a smooth, quiet recovery after anaesthesia
What do you administer is an animal is salivating a lot?
A drying agent e.g. anticholinergic and dry everything out.
What do we want drugs to have a minimal impact upon?
The cardiovascular system and minimal respiratory depression.
Would should breathing be like following premedication and why?
The animal will not be intubated until after induction, therefore the animal should be breathing spontaneously after premedication.
What should premedication provide and include?
Analgesia e.g. opioids.
What is a very beneficial feature of premedication?
Reversible - hasten the recovery from anaesthesia.
What do alpha 2 agonists cause?
Induce vasoconstriction!
What do alpha 2 agonists mimic?
The affects of adrenergic sympathetic nerve activation.
What are the effects of alpha 2 agonists?
Potent sedative and analgesic drugs.
What was the first alpha 2 agonist to be used in veterinary?
Xylazine
What was xylazine superseded by in dogs and cats?
Medetomidine and dexmedetomidine
What are the three alpha 2 agonits used in horses?
Xylazine, detomidine and romifidine.
What is used in cattle for alpha 2 agonists?
Xylazine and detomidine
Why is xylazine considered more dangerous than dexmedetomidine?
Because xylazine is relatively unselective for alpha 2 agonists and therefore xylazine has an agonist effect on a1 receptors in the heart.
Why is dexmedetomidine the preferential alpha 2 agonist of choice in small animals?
Because it has superior selectivity.
Is xylazine still used?
Yes in equine and farm animals, however superseded in small animal medicine
What is medetomidine known as in small animal medicine?
Dexmed
What is the effect of sedation using alpha 2 agonists?
It is profound and dose related
What means that the dose of alpha 2 agonists can be reduced?
Synergism between alpha 2 agonists, benzodiazepines and opioids.
How do alpha 2 agonists provide good analgesia?
Through an agonistic effect at the spinal cord alpha 2 receptors.
What is the duration of analgesia using a 10ug/kg dose of dexmetomidine?
1 hour.
What happens to the dose of the induction and maintenance agents after alpha 2 agonists are administered?
The dose of induction and maintenance is dramatically reduced in small animals.
How do IV induction agents need to be administered and why?
They need to be administered slowly and the vein to brain time needs to be slowed.
What do alpha 2 agonists do to blood pressure?
They produce a biphasic response - initial increase and then a return to normal or slightly decreased value.
What happens to heart rate during alpha 2 agonist administration?
Heart rate is decreased.
In dogs, down to 45-60bpm (normal 60-140 bpm).
In cats, 100-120 bpm (normal 140-220bpm)
- this can be quite disconcerting
What other disconcerning affect do alpha 2 agonists cause?
They refine the mucus membrane colour away from the normal pink perfection.
What do alpha 2 agonists cause in healthy animals and what does this result in?
They cause a reduced cardiac output meaning less oxygen delivery to the CNS, heart, kidney and brain.
What does the impact on the heart mean for alpha 2 agonists?
They can only be used in HEALTHY animals, they cannot be used in sick animals.
What affects do alpha 2 agonists have on the respiratory system?
Minimal effects on the respiratory system of healthy animals.
Why is urine production increased after the administration of alpha 2 agonists.
There is a reduction in vasopressin (ADH) and renin secretion (increases bp and perfusion to the kidneys).
In which species is this increase in urine production most noticable?
Hoses - within a few minutes they can urinate profusely.
What does the increased urine production mean for some animals?
Animals with urinary obstruction e.g. male cat with urethra crystals - do not give alpha 2 agonists WITHOUT cystocentesis as this could burst the bladder.
What is the most appealing factor associated with alpha 2 agonists?
They allow incredible reduction of the induction agent.
Why is there a biphasic response in BP when alpha 2 agonists are administered?
Because the blood pressure goes up and the heart rate slows down.
What happens to insulin levels when alpha 2 agonists are administered? what does this mean?
Endogenous insulin secretion is reduced leading to hyperglycaemia.
This means that unstable diabetics should not use these drugs.
What effect do alpha 2 agonists have on the liver?
Both liver blood flow and rate of metabolism of other drugs is reduced.
What reduces heat loss when alpha 2 agonists are administered?
Peripheral vasoconstriction
What is the benefit of administering alpha 2 agonists over acepromazine?
The peripheral vasoconstriction of alpha 2 agonists means it is easier to maintain normothermia during the peri-operative period.
What species are quite sensitive to alpha 2 agonists and why?
small ruminants because a lot of sheep have sub-clinical respiratory disease.
What rapidly reveres the alpha 2 sedation and analgesic effects?
Atipamezole - a specific alpha 2 adrenergic antagonist.
Why is reversal advantageous?
Because the recovery period is a high-risk time for anaesthetic complications.
How do you administer atipamezole and why?
IM.
Would not administer IV because this produces a very rapid, excitable recovery from anaesthesia.
In what species is atipamezole rarely used?
In cattle and horses.
What is the easy detomidine agent used in horses? what are the pros and cons of this?
Domosedan gel - oromucosal gel.
- oral administration takes the longest time for onset
- oral administration is the shortest duration
What is the most common/ licensed phenothiazine?
Acepromazine
What does acepromazine achieve?
Sedation and anxiolysis.
What happens with larger doses of acepromazine?
The longer the duration
The quality and reliability of duration can be improved with what?
The addition of an opioid.
-neuroleptanalgesia
What is an additional advantage of adding an opioid?
Adds analgesia, which is not a direct effect of acepromazine.