Premediacations Flashcards
What is a pre-med
A combination of drugs, or sometimes a single agent, given prior to anaesthesia.
Name the 2 types of anaesthesia which do not require a pre-med
Triple and quad anaesthesia for cats undergoing neutering
Name the different classes of drugs which can be used as part of a pre-med and give an example of each (x7)
Opioid e.g. methadone
Alpha 2 agonist e.g. medatomidine
Benzodiazepine e.g. midazolam
Ketamine
Phenothiazine e.g. ACP
Alfaxalone
Anticholinergic e.g. atropine
Give 6 reasons why we premedicate
- Balanced anaesthesia
- Sedation
- Agent/MAC sparing
- Provides preemptive analgesia
- Stress reduction
- Improved recovery
In what situation might you use an anticholinergic in the premed and why
BOAS undergoing respiratory tract surgery
Helps to reduce tract secretions
Give examples of opioids licensed in veterinary (x5)
Methadone
Fentanyl
Buprenorphine
Butorphanol
Pethidine
What does an opioid provide as part of a premed
Sedation
Analgesia
Name the 4 opioid receptors
Mu - full or partial mu agonists
Kappa
Delta
Nociceptin
Give 3 examples of a full mu agonist
Methadone, Fentanyl, pethidine
Give an example of a partial mu agonist
Buprenorphine
Name an opioid which is a mu antagonist and a kappa agonist, and what does this mean
Butorphanol
Good sedation, poor and short-lived analgesia
How do opioids affect: cardiovascular system, respiratory system, GI motility, gastric emptying
Minimal cardiovascular depression
Minimal respiratory depression - more so with fentanyl
Reduced GI motility
Decreased gastric emptying
Name the drug which antagonises opioids
Naloxone
Give some examples of alpha 2 agonists (x5)
Medetomidine
Dexmedetomidine
Detomidine
Xylazine
Romifidine
Which 2 alpha 2 agonists are most commonly used in small animal practice
Medetomidine
Dexmedetomidine
Why is Xylazine used less in small animals practice than other alpha 2 agonists
Relatively poor affinity for the alpha 2 receptor
Therefore has more side effects
Which 3 alpha 2 agonists are licensed in horses
Xylazine
Romifidine
Detomidine
What effects do alpha 2 agonists have
Profound dose-dependant sedation
Analgesia via alpha 2 receptors in the spinal cord (short-lived)
Marked drug-sparing effects
- MAC sparing
How do alpha 2 agonists affect blood flow to the CNS and why is this important
Increase the amount of time taken for injectables to reach the CNS
Be careful not to inject too quickly if given an alpha 2
How do alpha 2 agonists affect blood flow to the liver and and why is this important
Reduce blood flow to the liver
Reduce hepatic metabolism of other agents you have given
How do alpha 2 agonists affect the cardiovascular and respiratory system, and describe
Cause minimal respiratory depression
Cause significant cardiovascular effect
- Initially, peripheral vasoconstriction => increased BP, reflex bradycardia
- after 15-20 mins BP and HR return to normal
Name some potential bad effects of alpha 2 agonists
Reduction in endogenous insulin production => transient hyperglycaemia
Cause emesis
Increased urine production
Name the antagonist for alpha 2 agonists
Atipamezole
Give an example of a phenothiazine used in veterinary (x1)
Acepromazine (ACP)
What effects does acepromazine have as part of a premed
Sedation
NO analgesia
How does acepromazine cause its effects (think receptors it acts on)
Centrally acting
Dopamine antagonist - blocks DI and D2 receptors
Blocks alpha 1, muscarinic and H1 receptors
How long does it take for acepromazine to take effect IM
Slow!!
30-40 mins
What potential bad effects can acepromazine cause in small animals
Vasodilation mediated by alpha 1 antagonism => hypotension and hypothermia
Boxers have a high sensitivity => fainting/passing out
Name the antagonist for acepromazine
There isn’t one!
Give examples of benzodiazepines (x2) and which species are they licensed in
Diazepam - dogs and cats
Midazolam - horses, commonly used in small animal too
Why is it better to give diazepam IV compared to IM
Cause pain on IM injection and poorly absorbed
What receptor do benzodiazepines act on
GABA-A receptor
What effects do benzodiazepines have as part of a premed
Causes sedation, hypnosis and anxiolysis
NO analgesia
Poor level of sedation in a healthy animal - normally only given to sick patients
Why are benzodiazepines good to use in sick/compromised patients
Cause minimal cardiovascular and respiratory depression
Reduce amount of induction and inhalation agent needed
Anti-convulsants
What drug antagonises benzodiazepines and why isn’t it used in first opinion practice
Flumazenil
Short-lived - needs to be repeated
Very expensive
What type of drug is ketamine
NMDA receptor antagonist
Which 2 opioids demonstrate some NMDA receptor antagonism
Methadone
Pethidine
In what ways is ketamine dose dependant
High doses - a dissociative anaesthetic
Low doses - sedation
Why is ketamine good in a premed
Drug sparing - inhalation and induction
Good cardiovascular stability
Can cause dose dependant respiratory depression - only of concern at anaesthetic doses
What effects on parameters does ketamine have, and when is this an important consideration
Causes a transient increase in cardiac output and blood pressure
Can cause a reduction in BP in some sick patients
Some animals may not be able to cope with the stimulation produced by higher doses => think about use in cats with hypertrophic cardiomyopathy (HCM))
How long do the effects of ketamine last
30-45 mins
Is ketamine a good muscle relaxant
No - use in combination with a drug which causes good muscle relaxation e.g. midazolam or alpha 2
What is the effect of ketamine on the eyes
Drying to the corneas
The eye can be centralised even when the animal is fully anaesthetised as it preserves cranial nerve reflexes
Give examples of anticholinergics (x2)
Atropine
Glycopyrrolate
What are the effects of anticholinergics as part of a pre-med
which drugs should you never use them with
Reduce bradycardia - sometimes used in response to a drop in HR (DON’T if used alpha 2)
Reduce respiratory tract secretions
What are some unwanted effects of anticholinergics (x3)
Mydriasis (pupil dilation)
Reduced gut motility
Bronchodilation
What class of drug is alfaxalone
Neuroactive steroid
What are the effects of alfaxalone when used in a premed
Induction agent
Sometimes used to sedate sick patients
What system does alfaxalone have adverse effects on
Cardiovascular system,
What are the 3 pharmacokinetic properties required of drugs used in premeds
Relatively rapid onset - readily absorbed
Centrally acting - distributes to the brain
Relatively short acting - short elimination time
What is the time of onset and the duration of action of alpha 2 agonists
Rapid onset of action e.g. 5 mins for Xylazine in cattle
Short duration of action e.g. 40 mins for detomidine in horses
Which alpha 2 agonist has the greatest selectivity for the alpha 2 receptor
Dexmedetomidine > medetomidine > Xylazine
Which 2 of the 4 opioid receptor types are we most interested in for analgesia and sedation
Mu and Kappa receptors
Do phenothiazines (ACP) cross the BBB and placenta
Yes
Do phenothiazines (ACP) have a long or short duration of action and onset of action
Released slowly from fat - longer onset of action
Slow elimination, half-life of 24-48 hours - longer duration on action
What properties of benzodiazepines allows them to be absorbed orally and by IM
High lipid solubility
What organ metabolises benzodiazepines
Liver
How long after ketamine administration will the patient begin to regain consciousness
15-20 mins
