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What was xylazine superseded by in dogs and cats?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Yes in equine and farm animals, however superseded in small animal medicine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.
How can sedation be maximised following phenothiazine administration?
The animal should be left undisturbed for 30-40 minutes.
Is acepromazine a more or less reliable sedator than dexmedetomidine?
Less reliable sedation
What colour is ACP (acepromazine)?
A yellow liquid
Is there a reversal agent for ACP?
No
What can a side effect of ACP be?
Vasodilation.
Which is a more potent sedator? Acepromazine or alpha 2 agonists?
Alpha 2 agonists.
What receptors does ACP target?
Apha 1 adrenoreceptors.
What does ACP cause?
Vasodilation and a fall in arterial blood pressure.
What two conditions do we need to avoid the use of phenothiazines in?
Animal with CVS disease (cyclic vomiting syndrome) or animals in shock.
Why do we need to avoid acepromazine in hypotensive animals?
because it has a long-lasting and non-reversible effect.
Name one property of acepromazine which might be beneficial during anaesthesia?
Anti-arrhythmic properties.
What happens to body temperature when acepromazine is administered?
There is a reduction in body temperature due to peripheral vasodilation and resetting of thermeregulatory mechanisms.
What is one of the main risks of using phenothiazines?
The animals can get quite cold due to vasodilation.
Is acepromazine okay to use in epileptics?
Yes, but need to reduce its dose.
How are you supposed to dose Acepromazine and why?
Per body surface area rather than weight because large breed dogs are more sensitive to acepromazine therefore require a smaller dose.
Does acepromazine alter seizure threshold?
No evidence of this.
Name 2 conditions which acepromazine has caused in boxers?
- acepromazine induced orthostatic hypotension
2. vasovagal syncope (drop in heart rate and blood pressure)
How should acepromazine be administered in Boxers?
A very low dose (<0.01mg’kg) and animals should be monitored carefully after administration.
What is acepromazine?
It is a dopamine antagonist.
In what animals is acepromazine contraindicated and why?
Breeding stallions
- Paralysis of the retractor penis muscle can cause protrusion of the penis and swelling where the penis can not enter the sheath and in some cases, this has lead to amputation.
When acepromazine is administered, what do the owners have to look out for?
Make sure that the penis is retracted within 2-3 hours. can use reversal agent, penis support or manua compression (Esmarch bandage).
What is advised when administered to male horses?
Administer the lowest dose possible.
Name two commonly used benzodiazepines?
Midazolam and diazepam.
Do benzodiazepines cause sedation?
None in small animals.
What are benzodiazepines commonly mixed with in dogs and why?
Opioids because they are both cardiovascularly stable and cause reliable sedation.
In cats, what is the problem with benzodiazepine and opioids and how is this resurrected?
This is not a very potent sedative therefore ketamine and benzodiazepines are most commonly used.
Have midazolam and diazepam got market authorisation?
MA coming for midazolam, MA for diazepam in France.
Are benzodiazepines useful on their own? When are they useful?
They provide minimal sedation in healthy dogs and cats however provide good sedation when combined with opioids in dogs, or ketamine.
Why are benzodiazepines used as premeds in animals with cardiac disease?
because they have minimal effects on the cardiovascular system.
What are benzodiazepines commonly used for as a first line intervation?
Animals with epilepticus.
On what receptors do benzodiazepines work?
GABA receptors.
How can benzodiazepines be administered to epileptic animals?
Rectally as a gel.
Name the 7 pre-medication drug combinations that can be used in dogs and cats?
- Acepromazine + opioid
- Alpha 2 agonist + opioid
- Alpha 2 agonist + BZD
- Alpha 2 agonist + ketamine (cats)
- BZD + ketamine (cats)
- BZD + opioids
- Alpha 2 agonist + opioid + BZD
What 7 factors should help you to chose which premed to use?
- reason for anaesthesia or sedation
- duration of sedation required
- Procedure to be carried out
- Degree of pain expected
- Species and breed e.g. boxer
6/ Age of the patient e.g. geriatric - lower dose - ASA classification
What is the ASA classification of an animal with a systemic disease that is well stabilised on medication?
ASA 3
What is the ASA classification of a dog presented with GDV that has severe haemorrhagic compromise?
ASA 5
What is the sedation property of acepromazine?
Less effective than dexmedetomidine, usually add an opioid.
What is the analgesia affect of acepromazine?
No analgesia
What are the respiratory effects of acepromazine?
Minimal effect
What are the drug sparing effects of acepromazine?
Minimal drug sparing
What is the reversibility of acepromazine?
Not reversible
What is the sedative effect of dexmedetomidine?
Potent sedation, animals can still be aroused
what is the analgesic effects of dexmedetomidine?
Potent analgesia
What are the CV effects of dexmedetomidine?
Reduced CO, vasoconstriction, narrower safety margin. use only in animals with normal CVS.
What are the respiratory effects of dexmemetomidine?
Minimal effects
What is the drug sparing effect of dexmedetomidine?
Potent drug sparing effect
What is the reversibility of dexmedetomidine?
Reversible (atipamezole)
What would I use for ASA 1 dogs?
Dexmedetomidine or medetomidine
What would I use for ASA 2 dogs?
Depends on underlying reason for classification as ASA 2 - if not disease that affects CVS or liver function, can use dexmedetomidine.
If it is, use acepromazine and opioid.
What would I use for ASA 3 dogs?
Acepromazine and opioid.
depends on the illness - will the cardiovascular system cope with increased vasodilation caused by acepromazine?
Otherwise, benzodiazepine + opioid. This is the ‘cardiovascilar friendly’ combination.
What about an ASA 4 animal?
Benzodiazepine + Opioid.
What about an ASA 5?
Low doses of opioids and benzodiazepines prior to anaesthesia.
-distinct premedication is not usually required in very sick patients, instead, co-induction with madazolam and propofol, alfaxalone or ketamine. This will reduce the dose of the induction agent - improved cardiovascular stability.
What is a strong analgesic which could be used for dogs about to die?
Fentanyl
ASA 1 cats?
Dexmedetomidine
- IV access after light sedation with acepromazine can be difficult
- the reversibility is advantageous
ASA 2 cats?
Acepromazine + opioid
- might be able to use dexmedetomidine, depends if it is because of cardiac disease or liver function.
ASA 3 cat?
Acepromazine + opioid depending on CVS.
- could use BZD + ketamine (2.5-5mg/kg IM)
What will happen if higher doses of ketamine are used at premedication?
This will induce anaesthesia (10mg/kg IM)
ASA 4 cat?
Benzodiazepine + ketamine
- or opioid alone (buprenorphine, morphine, methadone - might be enough in quiet cats)
- benzodiazepine + opioid = not stable sedation
ASA 5 cats?
-low dose BZD and opioid at time of induction = balanced anaesthesia tecnhique
What would you use for emergency TIVA? (Total IV anaesthesia)
Fentanyl + midazolam at induction
What are anticholinergics used for in premedication?
Routine premedication with anticholinergics (atropine, glycopyrronium) is unnecessary.
they have nbeen used in the past with irritant inhalants to reduce bronchial secretions and opioids to offset bradycardia.
When should we not use anticholinergics?
To offset alpha 2 agonist bradycarda
What is the rule with acetylcholinergics at pre-med?
Only use where required, not routinely
Give two examples of an anticholinergic?
- atropine
2. Glycopyrronium
Name 2 contraindications of using anticholinergics in cats and ruminants?
They exacerbate bradycardia before HR increases with atropine and can thicken saliva and cause blockages.
What is a contraindication of using aanticholinergics in horses with colic and bloat in ruminants?
Inhibits peristalsis
Name three things that anticholinergics cause?
- mydriasis
- corneal drying
- Bronchodilation
When should you medicate patients?
So that the peak drug effect coincides with the induction of anaesthesia.
Where does the dose and drug need to be recorded?
On the anaesthesia record chart on the front of the cage.
Which is the preferred route of administration for premedication drugs?
IM over IV (except maybe rabbits which dont like this so maybe try SC?
Dose drugs according to what?
Lean body weight rather than obese body weight.
Why chose IM over IV administration?
More reliable distribution
If you have a difficult cat, what is recommended?
1IM injection containing both pre-med and induction. combine alpha 2, opioid, ketamine and benzo, all in one syringe.
What about an angry animal?
Don’t pre-med - give all in one!
generally in dogs and cats, which is slower to take effect, acepromazine (phenothiazine) or alpha 2 agonist?
Acepromazine.`
What are benzodiazepines reversible and is it readily available?
Flumazenil (not readily available)
What are opioids reversible with?
Naloxone.
