Premedication Flashcards
What is premedication?
Provision of sedation & anxiolysis before induction of anaesthesia
What are the benefits of premedication?
Reduction of dose of induction agent
Reduction of dose of maintenance agent
Provide pre-emptive analgesia & preventive analgesia
Ensure smooth recovery
Prevent side effects associated with other anaesthetic drugs
Can start at home in anxious animals
Define pre-emptive analgesia
Administration of analgesic drugs prior to onset of noxious stimulation
Benefits:
- Reduces immediate post-operative pain
- Minimises intensity & duration of subsequent pain.
- Easier pain control with analgesics post-surgery.
- Prevents peripheral & central sensitisation.
Define multimodal analgesia
Combines different analgesics acting via different mechanisms or sites in the nervous system.
Benefits:
- Additive & improved pain relief
- Reduced drug doses minimise side effects
Define preventive analgesia
Combines multimodal and pre-emptive analgesia
Continues into the early post-operative period to maintain effective pain control.
Describe Acepromazine (ACP=
A phenothiazine
widely used premed in dogs, cats & horses
Usually used with opioid (neuroleptanalgesia) because synergism occurs
Interferes with dopamine transmission to provide sedation
Can reduce blood pressure & oxygen delivery to tissues
- due to reduction in haemoglobin concentration caused by splenic sequestration of RBC
SC, IM, IV & oral
Define Neuroleptanalgesia
state of sedation & analgesia induced by combining neuroleptic (sedative) & opioid analgesic, commonly used for minor procedures & premedication
What are the most commonly used drugs to produce neuroleptanalgesia
Phenothiazine agents
α2-adrenoceptor agonists
Opioid analgesics
Administering these drugs together produces synergistic effects (greater sedation and analgesia than when given individually).
What a-2 agonists are used in small animals
Medetomidine & dexmedetomidine
What a-2 agonists are used in horses
Xylazine, detomidine & romifidine
What a-2 agonists are used in cattle
Xylazine & detomidine
Describe a-2 agonists
Profound cardiovascular effects (dose dependent) & reduction in cardiac output
increased urine output
Produces miosis (pupil constriction), decreased IOP (intraocular pressure) & decreased CBP (ciliary body perfusion) but vomiting possible
Atipamezole is the antagonist
Why are a-2 agonists (e.g. medetomidine & dexmedetomidine) a popular premed?
They provide reliable sedation, analgesia, and muscle relaxation.
Dexmedetomidine is often preferred over medetomidine as it excludes biologically inert levomedetomidine.
Why is xylazine not recommended for premed in dogs & cats?
Xylazine is associated with higher risk of mortality compared to other α-2 agonists & safer alternatives like dexmedetomidine are available
How do a-2 agonists cause sedation?
- α-2 Receptor Activation: Stimulates α-2 adrenoreceptors in CNS
- Inhibition of Adenylyl Cyclase: Reduces cyclic adenosine monophosphate (cAMP)
- Hyperpolarization: Potassium efflux & calcium channel inhibition prevent calcium entry into nerve terminals
- Suppression of Neural Firing: Decreases norepinephrine release in noradrenergic pathways
- Reduced Ascending Pathway Activity: Leads to sedation and hypnosis.
What cardiovascular effects do a-2 agonists cause?
Initial phase: Intense vasoconstriction, increased blood pressure & reflex bradycardia
Later phase (20–30 min): Vasoconstriction wanes, blood pressure normalizes, but heart rate remains low due to centrally mediated sympatholysis.
How do a-2 agonists provide analgesia
They inhibit nociceptive neurons in dorsal horn of spinal cord & reduce substance P release
Describe Benzodiazepines
E.g. Midazolam (water soluble), diazepam, zolazepam, alprazolam (others are dissolved in propylene glycol)
Work on GABA
effects:
- anxiolytic
- muscle relaxation
- cardiovascular stability
No analgesia
Suitable for ASA III-V patients
Avoid in healthy patients (causes excitement)
Antagonist is flumazenil
Often combined with:
- opioids
- ketamine
- alfaxalone
Describe Alfaxalone
IV or IM induction agent
Combined with other drugs (e.g. opioids) for sedation/pre-med
Useful option instead of a-2 agonists
Minimal effects on cardiovascular system
Drawback is large volume (IM) in big animals (painful)
Describe opioids
Used to provide pre-emptive & preventive analgesia & synergism with sedatives
Mild sedation when given alone to ASA I-II but more profound with ASA III-V
Limited cardiovascular effects
What is the difference between opiates & opioids?
Opiates: Drugs derived directly from opium (e.g., morphine, codeine).
Opioids: Includes naturally occurring, semisynthetic & synthetic substances with morphine-like activity acting at opioid receptors
What are the main uses of opioid analgesics?
Management of acute trauma pain
Pain relief during surgical or diagnostic procedures.
Treatment of painful medical conditions.
Long-term analgesic therapy for chronic pain, such as cancer-related pain.
Why are opioids referred to as narcotic analgesics?
They provide analgesia but can also induce sedation, euphoria, or sleep-like state (narcosis)
What are the legal requirements for Schedule 2 opioids in the UK?
Majority of opioids
Require prescription for requisition
Stored in a lockable cupboard meeting specific criteria.
Prescription/dispensing recorded in bound controlled drug register kept for 2 years.
Destruction of stock witnessed by authorised person or RCVS member unaffiliated with the practice.
What are the key characteristics of schedule 3 opioids?
Require requisition & storage in locked cupboard
Buprenorphine (only relevant schedule 3 opioid in VetMed) doesn’t require entry in controlled drug register
Butorphanol is not classified as a controlled drug in the UK.
What are the advantages of single-dose vials over multi-dose vials for opioids?
Single-dose vials: Simplify record-keeping by being prescribed & dispensed to single patient
Multi-dose vials: More prone to discrepancies due to needle hub & syringe dead space
What are the partial & full agonists of opioids?
Partial agonists: Drugs like buprenorphine that activate opioid receptors but with ceiling effect
Full agonists: Drugs like morphine or fentanyl that fully activate opioid receptors for maximum analgesic effect.
What are the 3 main opioid receptor types & what do they regulate?
μ (Mu): Spinal & supraspinal analgesia, sedation, euphoria, miosis (dogs), respiratory depression, decreased GI motility
κ (Kappa): Spinal & supraspinal analgesia, mild sedation, dysphoria, diuresis, miosis
δ (Delta): Spinal & supraspinal analgesia, cardiovascular depression.
Where are opioid receptors found & what do they mediate?
Found in the CNS, peripheral tissues (e.g., GI tract, joints after inflammation)
Mediate inhibition of pain
Describe the species, route of admin, duration, receptors & side effects/considerations for the following opioid:
Morphine (CD2)
Species: horse, cat, dog
Route: IM (SC, slow IV)
Duration: 4h (dog), 6-8h (cat)
Receptors: full MOR agonist
Side effects/considerations:
- vomiting
- histamine release
Describe the species, route of admin, duration, receptors & side effects/considerations for the following opioid:
Methadone (CD2)
Species: horse, dog, cat
Route: IM (SC, slow IV)
Duration: 4h
Receptors: full MOR agonist
Side effects/considerations: high dose
Describe the species, route of admin, duration, receptors & side effects/considerations for the following opioid:
Pethidine (CD2)
Species: horse, dog, cat
Route: IM (SC cats)
Duration: 1-1.5h
Receptors: Full MOR agonist
Side effects/considerations: histamine release
Describe the species, route of admin, duration, receptors & side effects/considerations for the following opioid:
Fentanyl (CD2)
Species: dog, cat
Route: IV (IM)
Duration: 0.3h
Receptors: full MOR agonist
Side effects/considerations: decreased heart & respiratory rate
Describe the species, route of admin, duration, receptors & side effects/considerations for the following opioid:
Butorphanol
Species: Horse, dog, cat
Route: IM, IV (SC)
Duration: 1h
Receptors: KOR agonist & MOR antagonist
Side effects/considerations:
- limited analgesia
- good sedation
Describe the species, route of admin, duration, receptors & side effects/considerations for the following opioid:
Buprenorphine (CD3)
Species: horse, dog, cat
Route: IM, IV (SC)
Duration: 6-8h
Receptors:
- partial MOR agonist
- KOR antagonist
Side effects/considerations: slow onset
What other drugs can possibly be given before induction
Anticholinergics
Antihistamines
H2 receptor antagonists & gastroprotectants
Anti nausea/vomiting medication (maropitant) & NK1 antagonism
Lidocaine IV
Steroids or NSAIDs
Antibiotics
How do we choose premed?
History, physical examination
ASA classification
Pain management
Breed and BCS
Age
Temperament
Current drugs being given
Drug availability in practice
Fill in the ASA status table
just know like 1 example
What premed would you use in ASA-I dogs & cats
Acepromazine or alpha-2 agonist + opioid
What premed would you use in ASA-II dogs & cats
Combination depends on disease
Low dose ACP/a-2 agonist & opioid usually tolerated
Care with ACP in liver disease
Care with a-2 agonists in CVS disease (e.g. mitral valve disease), ACP may be better option
a-2 agonist may be of use in HCM (low dose)
What premed would you use in ASA-III-V dogs & cats
Avoid a-2 agonists in compromised animals
Low doses of a-2 agonist may be useful if animal is very distressed
Opioid alone may be sufficient to sedate patient (e.g. methadone or butorphanol)
Ketamine & midazolam (IM or IV) in cats (not in hypertrophic cardiomyopathy)
Alfaxalone & opioid (but high volume of injectate)
- can add Benzodiazepines (e.g. Midazolam or Diazepam) too
What premed would you use in fearful/aggressive patients
a-2 agonists alone often insufficient to sedate
a-2 + ketamine + opioid (+- acepromazine) combination IM
Care with handling, environment, equipment, route & pheromones
If possible dispense medication for admin at home
- Gabapentin & Trazodone
- Alprazolam or diazepam
What are the steps in anaesthesia preparation?
- Consider signalment & take a history
- Include anaesthesia history
- Examine animal
- Consider additional diagnostics
- Decide on ASA category
- Discuss the risks with owner
- Gain informed consent
What should you do prior to undertaking anaesthesia in small animals
Consider starvation period
Weigh the animal
Plan anaesthetic & analgesic
Prepare anaesthesia equipment
Prepare drugs and IV fluids
Start to complete anaesthetic record
What should you do prior to undertaking anaesthesia in horses
Before horse GA – remove shoes, clean out feet, flush out mouth, groom
Weigh
Prepare theatre, consider animal position during GA
Place IV cannula
What is the purpose of an IV catheter during GA/sedation?
intravenous (IV) catheter is patient’s lifeline while under effects of GA & sedation
IV access allows for direct administration & rapid uptake of anaesthetic, analgesic & emergency drugs as required perioperatively
What cannula would you use in a rabbit vs horse vs dog
Short stay 22g cannula in auricular vein of rabbit
14g in jugular vein of horse
20g in cephalic of a dog
Acepromazine & buprenorphine
Medetomidine & methadone
Methadone
Dexmedetomidine & methadone
Medetomidine & buprenorphine
Administer methadone and antihistamine
Administer low dose acepromazine and methadone
Acepromazine
0.12ml medetomidine and 0.36ml methadone
dog is 12kg
0.12ml dexmedetomidine and 0.8ml buprenorphine
2.75ml ACP and 1.1ml butorphanol
How long should you fast a rabbit for prior to an ovariohysterectomy?
Don’t fast it
What is approximate death rate in healthy dogs following anaesthesia (e.g. CEPSAF study)?
PS this is quite an important figure to know - as owners may well ask about risk
1/600
Routine pre-anaesthesic blood testing is warranted in which of the following patients?
In patients requiring preanaesthetic stabilisation
In geriatric patients
In patients undergoing invasive surgery, with a high risk of haemorrhage
Which dog breed is prone to regurgitation during anaesthesia?
Brachycephalics
Which dog breeds are prone to opioid induced dysphoria?
Alaskan breeds
Labrador retrievers
Which dog breeds can suffer from a gene mutation leading to sensitivity of some anaesthetic drugs and ivermectin?
Collies
Which opioid is a full mu opioid receptor agonist (MOR), NMDA receptor antagonist, and affects noradrenaline re-uptake and is an excellent analgesic?
Methadone
If a collie had a MDR1 gene mutation, which anaesthetic drug would they be sensitive to?
Acepromazine
Which sedation/premedication drugs are available as oral gels for horses?
Acepromazine & Detomidine
Which drugs could be used to antagonise a methadone overdose?
Butorphanol
Naloxone
Moth is a 4 y/o siamese recently diagnosed with hyperthyroidism. Moth does not travel well, and is very fearful in the consult room. The owners have started oral medication for moth, but Moth needs monthly blood tests. Suggest drugs the owners can give orally to moth before she travels.
Gabapentin & Trazodone
Kai is an uncooperative XL Bully of approx 50kg with a bite history that requires sedation prior to anaesthesia for removal of a grass seed that he has inhaled as he has a sudden onset sneezing of blood tinged fluid. The dog is muzzled and the owner can restrain him for a short period of time for an IM injection. What would you like to inject the dog with?
Dexmedetomidine, ketamine, butorphanol and acepromazine
