Sedation and Premedication Flashcards
What is premedication?
Administration of medication prior to anaesthesia, giving sedative and analgesic effects
What are the aims of premedication?
Reduce anxiety Facilitate handling Contribute to peri-operative analgesia Facilitate smooth anaesthetic induction Reduce the dose of anaesthetic agent
What are anticholinergics used for in anaesthesia?
Mimicking action of efferent fibres of the vagus nerve
- Increase vagal tone (e.g. to counteract bradycardia)
- Vagomimetic drugs (opioids)
- Ressuscitation (atropine)
What are the major effects of anticholinergics?
Increase HR Bronchodilation Decrease secretions Mydriasis Reduced GI motility
In what animals would glycopyrrolate be a better choice that atropine?
Animals where you do not want any central effects and pregnant animals - does not cross the BBB.
How do anticholinergic agents act?
They block the neurotransmitter acetylcholine in the central and peripheral nervous system.
What are the three categories of anticholinergics?
Antimuscarinic agents
Ganglionic blockers
Neuromuscular blockers
What can anticholinergic drugs be used to treat?
GI disorders Genitourinary disorders Resp disorders Sinus bradycardia Insomnia Dizziness
What does anxiolytic mean?
A medication that inhibits anxiety
What is a sedative?
A substance that induces sedation by reducing irritability or excitement
Define narcosis
A state of stupor, drowsiness or unconsciousness produced by drugs
What are the classes of sedatives?
Phenothiazines Butyrophenones Benzodiazepines Alpha 2 agonsts Opioids
Describe the physiological properties of phenothiazines
Highly protein bound (90%>)
+ so must consider hypoproteinemia and hypoalbuminaemia
+ animals with GI problems may be absorbing proteins insufficiently or have excessive renal excretion
+ increased free drug»_space; increased drug action
Lipophilic (cross placenta and BBB)
Hydrophilic (IM absorption)
Hepatic metabolism
Excretion via urinae and bile
What is the main reason for use of phenothiazines? How is it brought about?
Calming effect via blockage of dopamine receptors in the CNS
What are the effects of phenothiazines?
Peripheral vasodilation
Blockage of alpha1 receptors
Anti-emetic effect
Inhibition in the CTRZ
Anti-histamine effects
H1 receptor blockade
Which phenothiazine is licensed for use in animals?
Acepromazine
What are the positive properties of ACP?
Anxiolytic at low doses, sedative at high doses
Anti-arrhythmic effects
May be administered orally
What are the negative properties of ACP?
Hypotension
Bradycardia
Relaxation of cardiac sphincter
Decrease in PCV and TS
Late onset (30 mins)
Larger animals more sensitive
Concomitant use with adrenaline
Lowers the seizure threshold
Antithrombotic
Relaxation of retractor penis muscle in horses
How does ACP lead to hypotension?
Blockade of alpha1 adrenergic receptors leading to vasodilation
Why might ACP be contraindicated in brachycephalics?
More susceptible because they have higher vagal tone.
Causes relaxation of the laryngeal muscles and thus upper airway obstruction
Why might ACP be contraindicated in stallions?
Relaxation of retractor penis muscle in horses
mainly stallions but also in geldings
Priapism (persistent and painful erection of the penis) is also reported
Can result in trauma or paraphimosis (an uncommon medical condition in which the foreskin becomes trapped behind the glans penis, and cannot be reduced)
In which animals should you avoid the use of ACP?
Extemes of age Renal or hepatic disease Hypovolaemia and/or most shock states Brachycephalic breeds (Boxer?) Breeding stallions
What are the properties of butyrophenones?
Mostly acts on the same receptors as phenothiazines
Sedative action by dopamine antagonisms
Antiemetic properties
Vasodilation and hypotension
Describe the pharmacodynamics of azaperone…
Peak sedation 15-30mins if IM
Duration of action 2-3 hours
Decrease in HR, CO and ABP
Impaired thermoregulation
