Pre-medications and sedatives Flashcards
What are the ideal drug properties?
- Produce reliable sedation and anxiolysis
- Minimal effects on the CV and Resp system
- Provision of analgesia
- Reversibility
Why do we premedicate?
- Provide anxiolysis
- Facilitate animal handling
- Contributes to a balanced anaesthesia and smooth and quiet recovery
- Counter algesia and side effects of other drugs
What are the drugs used as pre-medication?
- Phenothalzines
- Alpha- 2 agonists
- Benzodiazepines
- Alfaxalone
- Anticholinergics
- Opioids
What is an example of a phenothalzine?
- Acepromazine
What are some examples of alpha-2 agonists?
- Dexmedetomidine
- Medetomidine
- Xylazine
What are some examples of benzodiazepines?
- Diazepam
- Midazolam
What are some examples of anticholinergics?
- Atropine
- Glycopyrronium
What are some examples of opioids?
- Morphine
- Methadone
- Pethidine
- Hydromorphone
- Oxymorphone
- Buprenorphine
- Fentanyl
- Butorphanol
How do phenothiazines work?
- Inhibits dopamine pathways, so calms patient this way
- Anti-emetic
- Reduces total anaesthetic dose by a third and protects against arrhythmias
- Has a sedation plateau
- Long duration of action (6 hours)
Why should phenothiazines be avoided in liver disease?
- Drug is metabolised by the liver
What does neuroleptanalgesia mean?
- Combination of an phenothiazine with an opioid
What are the effects of phenothiazines on the cardiovascular system?
- Inhibits alpha-1 adrenoreceptors, which leads to peripheral vasodilation and a reduction in arterial blood pressure
- Sequesters RBC to the spleen reducing HCT by 20%
What patients should be avoided when using phenothiazines?
- Liver disease
- Shock
- Cardiovascular disease
- Anaemic
- Having a splenectomy
- Epilepsy
What are the effects of phenothiazines on the respiratory system?
- Neuroleptanalgesia overdoses can lead to respiratory depression
What are the effects of phenothiazines on the body temperature?
- Associated with a decrease in body temperature due to resetting the thermoregulatory mechanism and peripheral vasodilation
What are the effects of phenothiazines on the gastrointestinal system?
- Lowers the oesophageal sphincter and increases the risk of gastro-oesophageal reflux
How do alpha-2 agonists work?
- Stimulate alpha-2 receptors found centrally and peripherally
- Reduces total anaesthetic dose of isoflurane by 70%
- Muscle relaxant
- When combined with opioids or benzodiazepines the sedative effect is synergistic and greater alowing reduced doses of A-2-A
What are the effects of alpha-2 agonists on the cardiovascular system?
- Biphasic dose dependent on blood pressure; two phases
- Phase 1: vasoconstriction leading to increased BP leasing to a reduction in HR
- Phase 2: BP returns to normal, but HR remains low, which can lead to issues with cardiac output and blood pressure
- Heart rhythm can lead to ventricular premature complexes or bradycardia abnormalities
What are the effects of alpha-2 agonists on the body temperature?
- Causes vasoconstriction, which minimises the heat loss
What are the effects of alpha-2 agonists on the neurological system?
- Lowers cerebral blood flow, which reduces intracranial pressure
What are the effects of alpha-2 agonists on the gastro-intestinal tract?
- Vomiting is frequently seen, so care with oesophageal obstructions, intraocular pressure, intracranial pressure and cervical disk disease
What is the reversal agent for alpha-2 agonists?
- Use of atipamezole and alpha-2 antagonist
Why alpha-2 agonist’s reversal agent administered IM and not IV?
- IV can cause excitability, tachycardia and very rapid recovery
How do benzodiazepines work?
- Depress the sub-corticol levels of the CNS working on GABA receptors
- Anxiolytic
- Muscle relaxant
- Anticonvulsant
- Stimulates appetite
- Reduces total anaesthetic dose
- Used in combination with opioid for pre-meds and sick or compromised patients
- Minimal effects on CV and respiratory system
