Pre-Medications Flashcards
Why give pre-meds?
- Provide sedation and analgesia
- Calm the patient for smooth induction
- Reduce dose of induction and maintenance agents required
- May help reduce some adverse effects of the anaesthetic or surgical procedure
What is balanced anaesthesia?
- Using multiple drugs in combo to achieve anaesthesia
- Provide better quality of anaesthesia
- Minimise total doses of agents used whereby reducing potential side affects
- All tailored to the individual patient
- Balance out side effects with other drugs
What are the golden rules to using Pre-meds
- correct does tailored to the individual animal!
- Should be given and left in a quiet environment
- Give enough time for the drug to take effect
- note the route of admin (may impact time to reach effect and duration of effect)
How long do most pre-meds take to cause an effect?
30 minutes
What are Alpha-2-Agonists ?
Drugs that bind to alpha-2 receptors in the brain and spinal cord
How do Alpha-2-agonists work ?
Block transmission of nociceptive impulses
Exact mechanisms not fully understood
What do Alpha-2-Agonists provide?
Sedation and Analgesia
Name 2 Alpha-2-Agonists
Medetomidine
Dexmedetomidine
What are Alpha-2-Agonists used for?
- Sedation
- Pre-medication
- Anaesthesia
What other drug to Alpha-2-Agonists work with for sedation?
Opioids (usually buprenorphine)
What is a major benefit when using Alpha-2-Agonists as pre-medication
Can achieve a profound sparing effect which lowers the doses of other agents required for induction and maintenance
What other drug is commonly used with Alpha-2-Agonists for anaesthesia
Ketamine - especially in cats
What analgesic approach can Alpha-2 Agonists be used as a part of
multi-modal analgesic approach
Name 4 potential side effects with Alpha-2-Agonists
- Causes vasoconstriction
- Can cause profound bradycardia
- Causes respiratory depression
- Reduces liver blood flow
- May cause vomiting
What patients should you not use Alpha-2-Agonists on or have extreme caution in using on
- Patients with cardiovascular disease
- Patients with liver disease
- Patients where vomiting would be risky
Name 4 advantages of Alpha-2-Agonists
- There is a reversal drug (Atipamezole)
- Profound drug sparing effect
- Provides muscle relaxation
- Provides Analgesia
- Duration and level of sedation are dose dependent
What are opioids?
Analgesics
Light sedative effects
How do opioids work?
Act by combining with specific receptors in the brain and spinal cord (OP3 most commonly) and decrease the transmission of noxious stimuli
What are the three kinds of Opioids?
Full agonists
Partial Agonists
Antagonists
How do full agonist opioids work and when would you use it?
Produce maximal effect and bind all receptors
Used for moderate to severe pain e.g. bitch spay
Give an example of a full agonist opioid
Morphine, methadone, pethidine, fentanyl
What other drugs are used in combo with partial agonist opioids
Alpha-2’s or phenothiazine
What form of pain is a partial agonist opioid use in and give an example of a partial agonist
Mild to moderate pain
Example: Buprenorphine
What is the function of an antagonist opioid?
Work against the analgesic effects of the agonist - can be used as an antidote
Give an example of an antagonist and where it is commonly found
Naloxone (‘Narcan’)
Often found in emergency crash kits
What kind of Pre-meds are opioids usually combined with
sedatives
Name 2 schedule 2 opioids
Morphine, fentanyl
Name 2 schedule 3 opioids
Buprenorphine, tramadol
Benefits of using an opioid?
- provide analgesia and euphoria, sedation
- Little effect on respiration at correct dose
- Drug sparing effect
- Little effect on CVS but can cause bradycardia
- Pain relief provided may improve ventilation in cases of thoracic wall injury
What negatives are associated with the use of opioids?
- High doses lead to profound respiratory depression
- Contraindicated in animals with increased ICP
- Vomiting may occur due to morphine
- Constipation
- Antitussive effect (suppress coughing)
- Urinary retention if given spinally
What are Benzodiazepines?
Tranquilisers
How do benzodiazepines work?
They enhance the neurotransmitter GABA
Name 2 examples of benzodiazepines?
Diazepam
Midazolam
What other pre-med is usually given in combination with benzodiazepines?
Opioids
When will benzodiazepines be given alone as a pre-med
when patients are very sick - may cause excitement if given alone in healthy patients
Why are benzodiazepines not given alone to healthy patients
May cause excitement
Name 3 benefits of benzodiazepines
- safe
- minimal effects on cardiovascular system
- minimal effects on the respiratory system
- Good muscle relaxation
- Anti-epileptic action
- Appetite stimulation
What benzodiazepine is good for anti-epileptic action and how would it be administered
Diazepam
Given IV
What negatives are associated with benzodiazepines?
- Can be unpredictable action
- Not sufficient premedication if used alone in healthy animals
- Diazepam is painful by I/M injection
What benzodiazepine should be given IV and what one should be given IM
IV - diazepam
IM - midazolam
How do Anti-muscarinics work?
Decrease the parasympathetic tone by blocking transmission via acetyl choline
Name 2 anti-muscarinics
Atropine
Glycopyrrolate
What nerve is the closely associated with the parasympathetic system?
Vagas Nerve
What do anti-muscarinics do?
- antagonise the parasympathetic nervous system
- prevent bradycardia
- dry up secretions
- Counteract high parasympathetic activity
Why did anti-muscarinics first become popular? And why are they less commonly used now?
Previous inhalational drugs would cause increase the activity of the parasympathetic system (bradycardia, increased secretions)
Our current inhalational drugs do not cause these side effects
Which anti-muscarinic is most commonly used?
Atropine
When are anti-muscarincs used? (name 3)
- eye surgery
- Laryngeal surgery
- Brachycephalics
- When reversing muscle relaxants
- Only when needed
What benefits are there with Anti-muscarinics (name 2)
- reduces salivation and bronchial secretion
- counteracts bradycardia
- helps prevent ‘vagal events’ during reversal of muscle relaxants
Name 3 negatives associated with anti-muscarinics?
- Caused increased heart rate
- Causes increased metabolic rate
- May cause arrhythmias
- Thickens bronchial secretions
- Gastrointestinal ileus
- Pupil dilations causing visual disturbance
- May have long lasting effects of a couple of hours
What do phenothiazine’s provide?
- Provide tranquilisation (sedation at higher dose)
- Do not provide analgesia
What are phenothiazines commonly used with?
Synergistically with Opioids
Name a phenothiazine
Acetylpromazine (ACP)
What is ACP commonly used with
Opioids
Buprenorphine or methadone
What forms do ACP come in
Tablet or injectable form
How long does ACP last
6 hours
How quickly does ACP come into effect
30-35 minutes
What does increasing the dose of ACP cause
prolonged period of sedation
NOT the deepening of sedation
What animals are more resistant to the effects of ACP ?
small dogs and cats - dosage is usually higher in them
What animals are usually more sensitive to ACP?
Big dogs and brachycephalics - smaller doses
What patients should phenothiazines be used with caution in?
- brachycephalics
- Epileptics
- Bradycardics
- Large breeds
- Hypo-volaemic or dehydrated patients
Benefits of phenothiazines? (name 3)
- Anti-emetic
- Smooth muscle relaxation
- Mild anti-histamine effect
- Relatively safe for respiratory system
- Relatively safe for cardiovascular system
- Usually a smooth recovery
What side effects are associated with phenothiazines? (name 2)
- Causes vasodilation and will lead to hypotension
- May cause hypothermia
- Controversial but some believe it may decrease seizure threshold
- Boxers have a habit of fainting due to large bread, brachycephalic, and suffer from hypotension
What negatives are associated with phenothiazines? (name 2)
- Slow peak effect
- Long duration of action
- No analgesia
- Unpredictable side effects
What is hypnorm licensed for use in?
Rabbits
What is hypnorm usually combined with
Opioid - fentanyl
makes it a composite drug
What does hypnorm contain that makes it behave the same way as phenothiazines?
Butyrophenone fluanisone
