Premedication

Question 1

What are the 5 classes of drugs used for premed?

Answer 1

Phenothiazines
α2 agonists
Benzodiazepines
Butyrophenones
Opioids

Question 2

What are the names of the licensed products of each class of premed drugs?

Answer 2

Phenothiazines = Acepromazine (ACP)
α2 agonists = Dexmedotomidine, Medotomidine (also Romifidine, Xylazine)
Benzodiazapines = Diazepam, Midazolam
Butyrophenones = Fluanisone (combination with Fentanyl = Hypnorm)

Question 3

List some key facts about acepromazine (ACP).

Answer 3

Clinical effects = sedation, anxiolysis
Often used in combination with opioids
Dose dependent up to plateau dose
Subcut = non-irritant and efficacious

Question 4

What are the physiological effects of ACP?

Answer 4

CVS - peripheral vasodilation, decreased BP, decreased body temp.
Anti-arrhythmic action

Question 5

What are the pharmacokinetics of ACP?

Answer 5

IV admin = 10-15 mins
IM admin = 30-40 mins
Long duration of action (4-6 hours)

Question 6

List some key facts about α2 agonists.

Answer 6

Clinical effects = sedation, analgesia, muscle relaxation
Potent
Duration/level of sedation/analgesia is dose dependent
Often combined with opioids
Reversible using atipamezole

Question 7

What are the physiological effects of α2 agonists?

Answer 7

CVS = bradycardia, reduced cardiac output, initial BP rise
Respiratory depression
Emetic
Depress GI activity
Transient hyperglycaemia
Complex effects on uterine contractility (risk of abortion)

Question 8

What are the pharmacokinetics of α2 agonists?

Answer 8

IV admin = 5 mins (peak at 30 mins)
IM admin = 15 mins
If not reversed, duration of action 2-3 hours

Question 9

List some key facts about benzodiazepines.

Answer 9

Clinical effects = minor tranquiliser, muscle relaxation, anticonvulsant
Good sedation in sick or young animals
Combine with opioids/ketamine/α2 agonist to improve sedation
Reversible with flumazenil

Question 10

What are the physiological effects of benzodiazepines?

Answer 10

CVS = minimal
Mild respiratory depression
Musculoskeletal system = muscle relaxation

Question 11

What are the pharmacokinetics of benzodiazepines?

Answer 11

Admin by slow IV

Short plasma half-life

Question 12

List some key facts about butyrophenones.

Answer 12

Fluanisone
Only available in combo with the opioid fentanyl (Hypnorm)
Licensed in rabbits, rats, mice, G pigs

Question 13

What are the pharmacokinetics of butyrophenones?

Answer 13

Duration of action 30-60 mins
If admin with BDZ good surgical anaesthesia with muscle relaxation for 20-40 mins
Moderate-severe respiratory depression

Question 14

Describe the ASA grading system for patients.

Answer 14

Grade 1 = normal healthy patient
Grade 2 = patient with mild systemic disease
Grade 3 = patient with severe systemic disease
Grade 4 = patient with severe systemic disease that is constant threat to life
Grade 5 = moribund patient not expected to survive without operation

Question 15

What are the premed protocols for Grade 1 and 2 patients?

Answer 15

ACP + opioid
α2 agonist + opioid
Fentanyl/Fluanisone +/- BDZ (RABBITS)

Question 16

What are the premed protocols for Grade 3 patients?

Answer 16

Dogs = ACP + opioid / BDZ + opioid
Cats = BDZ (midazolam) + ketamine
Rabbits = BDZ + opioid

Question 17

What are the premed protocols for Grade 4 and 5 patients?

Answer 17

BDZ + opioid
BDZ + ketamine
Opioid alone
No premed but higher doses of induction

Question 18

How do we care for sedated/premedicated patients?

Answer 18

Quiet environment
Observed regularly/continuously
Think ABC
Monitor temp, pulse, resp, MMs
Ideally record obs

Question 19

What can go wrong during premedication?

Answer 19

Excitement/excessive sedation
Airway obstruction
CVS effects (cardiac arrest)
No compensation for existing/hidden conditions
Something odd develops

Question 20

What is the difference between sedation and premedication?

Answer 20

Sedation does not involve a loss of consciousness, i.e. the animal is not under general anaesthetic.

Question 21

How is sedation used differently in farm animals than in small animals?

Answer 21

Farm animals = standing sedation and LAs commonly used to perform procedures including invasive surgery

Small animals = very unusual to perform procedures without the use of GA

Question 22

When is sedation appropriate in small animal practice?

Answer 22

Safe handling of anxious/dangerous/feral animals
Procedures that require the animal to be still, e.g. radiography
Minor procedures e.g. wound redressing, grass seed removal, de-matting