Induction Agents Flashcards
1
Q
What are the ideal properties of an injectable anaesthetic?
A
- Rapid onset
- Smooth induction of anaesthesia
- Smooth recovery
- Non-irritant to tissues
- Good bioavailability by all routes
- Short duration of action
- Non-cumulative
- Minimal side effects
- Muscle relaxation
- Analgesia
2
Q
What are the advantages of an injectable anaesthesia?
A
- Little equipment needed
- Usually easy to administer
- Induction can be rapid and smooth
- Relatively cheap
- No environment pollution
3
Q
What are the disadvantages of an injectable anaesthesia?
A
- Once given, retrieval is impossible
- Accurate weight required
- High doses to maintain sufficient anaesthesia when used alone
- Not well tolerated by debilitated, hypovolaemia or endotoxaemia animals
- Potential for human abuse
- Risks of inadvertent self-administration
4
Q
What are the pharmacokinetics for induction agents?
A
- IV agents go to the brain rapidly to act on GABA receptors
- Lipophilic drugs cross the BBB rapidly, which causes a fast induction of anaesthesia
- Once concentration is high enough, loss of consciousness occurs and then the drug travels to other organs
- Body fat acts as a storage area for lipophilic drugs
- Redistribution from brain and then adipose tissue allows the patient to wake up
5
Q
How do barbituates (Thiopental) work?
A
- Short acting
- Acts on GABA receptors
- Lipophilic, so crosses BBB quickly and therefore rapid onset
- No analgesia
- Slow metabolism and recovery, as high protein bound
- Recovery from redistribution to fat and muscle
6
Q
What are barbituates (thiopental) side effects?
A
- IV only, so very irritant
- Induction and mergence excitement possible; can reduce with premed
- Arrhythmogenic (sensitisation of myocardium to catecholamines)
- Mild hypotension causing mild tachycardia
- Mild respiratory depression
- Splenic engorgement
- Post-anaesthetic hangover which can leave for several days
7
Q
What patients should be avoided when using a barbituate (thiopental)?
A
- Splenectomy
- GDV
- Caesarean
- Sighthounds
- Cardiac arrythmias
- Hypovolaemia
8
Q
How do barbituates (pentobarbital) work?
A
- Less lipid soluble than thiopental, so slower crossing BBB
- Dose dependent anaesthetic for duration and depth
- No analgesia
- Minimal cardiovascular depression
- Significant respiratory depression
- Slow metabolism, so prolonged recovery
- Extravascular injection is irritant
9
Q
How do substituted phenols (propofol)?
A
- IV only
- Non-irritant
- Acts on GABA receptors
- Highly protein bound, so slow recovery
- No analgesia
- Rapid hepatic metabolism in dog, but absent pathway in cats, so slower recovery
- Cumulative in cats, so haemolytic anaemia
10
Q
What are substituted phenols (propofol) side effects?
A
- Myocardial depression and dilation of blood vessels causing hypotension
- Respiratory depression; can cause apnoea if rapid injection
- Smooth and rapid induction with a good recovery phase
- Can be used for caesarean, but allow time for maternal party to metabolise drug before removing neonates
11
Q
What are the 2 types of propofol?
A
- Emulsion containing benzyl alcohol (propofol plus); can be stored for 28 days
- Emulsion containing soya nad egg with no bacteriastat; cannot be stored once opened
12
Q
What patients should be avoided when using substituted phenols (propofol)?
A
- Hypovolaemia
- Heart failure
- Hyperlipidaemia or pancreatitis
13
Q
How do dissociatives (ketamine) work?
A
- Work on NMDA receptors in dorsal horn of the spinal cord
- Excreted unchanged in felines
- Excreted as metabolites in canine
- Can be given IV, IM and SC
- 50% protein bound
- Profound analgesia
- Light sedation
- Slow onset
- used with A-2-A and benzodiazepines to offset side effects
14
Q
What are the side effects of dissociatives (ketamine)?
A
- Muscle rigidity
- Tachycardia
- Hypersensitivity to noise
- Dilated, fixed pupils
- Stings on administration
- Amnesia
15
Q
What patients should be avoided when using dissociatives (ketamine)?
A
- Seizures
- Increased intracranial pressure
- Hypertrophic cardiomyopathy
