General anaesthetics - my q's

Question 1

IV side effects

Answer 1

• causes depression of the CNS
• results in lack of perception from senses
• but this results in decreased pain perception while the patient is still in a conscious state

therefore GA is given IV quite a bit

Question 2

types of medicines and their groups

Answer 2

1. Barbiturates
   a) thiopentone (pentobarbitone, phenobarbitone)
2. Other Meds
   b) alfaxalone
   c) propofol
3. Dissociative anaesthetics
   d) ketamine
   e) tiletamine

Question 3

Group one: barbiturates

Answer 3

• inhibit/reduce CNS excitability
• multiple therapeutic uses such as injectable GA, anti-epileptic drug & agent for euthanasia
• MOA: inhibit brain neurotransmitters to reduce CNS excitability by binding to chloride channels, causing them to open
• quick onset of action (seconds) but DOA is short
• has to be given quickly to achieve high peak plasma concentration (how quickly it’s administered determines its anaesthetic action
• metabolised in the liver
• dose given depending on body weight

Question 4

group two: other medicines

Answer 4

ALFAXALONE:

• acts on GABA as an agonist
• produces smooth induction and recovery from anaesthesia
• onset of action is quick (10 second) and is dose-dependent on DOA

PROPOFOL:

• acts to reduce GABA dissociation from GABA receptor
• smooth induction and recovery
• short DOA
• can be given through CRI
• metabolised by liver and lungs
• cardiovascular effects (bradycardia & hypotension)
• resp effects too

BOTH not suitable for fetuses

Question 5

group three: dissociative anaesthetics

Answer 5

• purpose is to have animal unresponsive but not asleep
• dissociates the thalamocortex & limbic system

KETAMINE

• antagonist of NMDA receptors
• also acts as an antagonist of glutamate R
• produces smooth recovery when used with diazepam
• S8 medicine
• always used with other drugs - never alone

TILETAMINE & ZOLAZEPAM
- similar action to ketamine

Question 6

Premedication general anaesthetics

Answer 6

• acepromozaine (most common)
• promazine
• chlorpromazine (rarely used)

Question 7

Acepromazine

Answer 7

• good absorption
• a D2 R antagonist
• inhibits central dopamine D2 receptors to produce sedation
• works to decrease anxiety, needing lower maintenance of anaesthetic drugs and therefore a balanced anaesthesia
• effects the CNS system, cardiovascular, resp, musculoskeletal (muscle relaxation)
• dose dependent - so increasing the dose reaches the maximum effect
• DONT USE in dehydrated, hypovolemic, bleeding, in shock or with coagulopathies
• be cautious with bracheocephalic, boxers, breeding stallions

Question 8

benzodiazepine

Answer 8

• bind to GABA receptor to activate the R
• provide sedation, skeletal muscle relaxation and anti-epileptic
• reliable in neonates, geriatrics, ill animals and small ruminants
  examples include diazepam, midazolam, zolazepam