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Anaesthesia > Induction of Anaesthesia > Flashcards

Induction of Anaesthesia Flashcards

1
Q

Injectable agents used for general anaesthesia

A 
Propofol
Alfaxalone
Ketamine
Thiopentone/Thiopental
Etomidate
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2
Q

Inhaled agents used for general anaesthesia

A 
Isoflurane
Sevoflurane
Halothane
Desflurane
Nitrous oxide
Xenon
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3
Q

Methods of administration for induction of anaesthesia

A 
Usually injectable (95%)
Most commonly intravenous
Can be intramuscular
Can be inhalational
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4
Q

What may choice of induction drug depend on?

A 
Species and temperament of animal
Underlying medical conditions
Nature of procedure
Available drugs, equipment and conditions
Personal preference and experience
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5
Q

Describe the continuum of GA agents

A

Dose dependent CNS depression
Sedation to anaesthesia
Low dose = sedation
High dose = anaesthesia

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6
Q

What are the stages of anaesthesia?

A
  1. Conscious patient (premedicated)
  2. Administration of anaesthetic agent
  3. Unconsciousness (phase1)
  4. Signs of excitement (phase 2)
    + Not if quick induction
    + eg. ketamine
  5. Surgical anaesthesia (phase 3)
  6. Overdose (phase 4)
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7
Q

What side effects will you see with GA eg. CVRS?

A

+++ CVS depression
Drop in CO
Vasodilation
Reduced blood pressure when monitoring

+++ Respiratory depression
Decreased respiratory rate
Decreased tidal volume
Reduced minute volume

DOSE DEPENDENT (when animal not stable use benzodiazepine as doesn’t have CVRS effect)

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8
Q

Do anaesthetic agents provide good analgesia?

A

No with the exception of ketamine.

Need to administer analgesic because nociceptors and pain reflexes still stimulated.

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9
Q

Propofol

  1. Route of administration
  2. Use
  3. Appearance
  4. Speed of onset
  5. Metabolism
A
  1. IV
  2. Induction and maintenance
  3. White emulsion containing lipid
  4. Rapid onset following injection
  5. Rapid metabolism
    + Hepatic and extrahepatic eg. lungs, gut, muscles
    + Can be used in animals with liver disease
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10
Q

Side effects associated with propofol

A

Cardiovascular depression
Vasodilation
Decreased blood pressure

Respiratory depression (dyspnoea)

Stiffness/tremors due to imbalance of neurotransmitters
+ May not want to use again
+ Give benzodiazepine to counteract

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11
Q

Why can’t propofol be given IM?

A

It is so lipid soluble that it would distribute everywhere and wouldn’t have high enough concentration to have required effect.

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12
Q

Describe the use of propofol in cats

A

Metabolism is slower than in dogs

Deficient in several conjugation pathways

Recovery slower

Cumulative

Daily anaesthesia may cause Heinz body production and oxidative injury (3-5 days)

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13
Q

Describe dosing of propofol

A

2-4mg/kg premedicated animals

Give very slowly to effect

Alpha2 agonists cause bradycardia = slower circulation = longer onset time

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14
Q

What is PropoFlo Plus?

A

Current propofol agent used
No pain on injection
Gives dogs and cats smooth, rapid inductions and recoveries
Milky white appearance
Rarely causes local tissue reaction with inadvertent perivascular administration
Licensed for induction
Use within 28 days

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15
Q

Alfaxalone

  1. Route of administration
  2. Use
  3. Speed of onset
  4. Speed of duration
  5. Side effects
  6. Dose
A
  1. IV or IM
  2. Induction and maintenance
  3. Rapid onset
  4. Short duration
    + Can see excitement on recovery if not adequately sedated
  5. Less cardiopulmonary depression than propofol
  6. Dose 2-5mg/kg IV
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16
Q

Ketamine

  1. Route of administration
  2. Use
  3. Actions
A
  1. IM or IV (only licensed for IM in dogs)
  2. Induction and maintenance
  3. Analgesic actions at subanaesthetic doses
17
Q

What happens if you give ketamine alone?

A

Excitation and rigidity.

Always combined with sedative agents.

18
Q

Describe the ‘Triple combination’ of ketamine induction

A 
Used in aggressive cats or dogs
Ketamine, medetomidine, opioid
IM (3-5min onset)
Single combined injection
Short duration
Dose 3-5mg/kg IM
19
Q

How is ketamine used in horses?

A

After profound sedation with alpha2 agonist

Dose in combination with benzodiazepine to counteract muscle rigidity

20
Q

Side effects of ketamine when inducing

A

CNS = cranial reflexes preserved
+ Makes intubation more difficult

CVS stimulation of sympathetic
+ Mild increase in BP and tachycardia
+ Direct myocardial depression

Mild respiratory depression

Analgesia

21
Q

Thiopentone/Thiopental

  1. Licensed
  2. Onset of action
  3. Metabolism
  4. Cumulative?
  5. Recovery time
  6. Preparation
  7. Side effects
A
  1. No
  2. Rapid onset
  3. Slow metabolism
  4. Accumulated in body fat with repeated injections
  5. Slow recovery
  6. Powder (have to reconstitute with water)
  7. CV and respiratory depression similar to propofol
22
Q

What is a problem with the use of thiopentone for induction?

A

Irritant if administered extravascularly (very alkaline).

Causes necrosis of skin and subcutaneous tissue.

23
Q

Describe the use of Etomidate

A

Minimal CV and respiratory depression

Good for sick/compromised patients

Depresses adrenal gland function (cortisol production)

Unlicensed

24
Q

Describe the use of fentanyl/midazolam combination for induction..

A

Opioid and benzodiazepine
Good for sick/compromised patients eg. GDV
Muscle relaxation and analgesia

25
Q

Describe the used of inhalational induction

A

Sevoflurane/isoflurane delivered in oxygen

Aggressive patients when IV impossible

Increased risk of pollution and personnel exposure

May see excitement/stress during induction

26
Q

What are the problems associated with isoflurane?

A

Irritant to respiratory passages

Breath holding during induction

Sevoflurane preferred (not licensed in cats)

27
Q

Describe inhalation agent uptake

A

Pressure gradient from vaporizer to brain
+ High pp in lungs = high pp in brain
+ But agents that are very soluble in blood will have lower pp in lungs = lower pp in brain
+ Speed of induction and recovery slower for more soluble agents

Vaporizer –> anaesthetic system –> alveoli –> blood –> brain

Need high flow rate to get high enough concentration (don’t use circle system).

28
Q

Describe monitoring during induction

A 
Critical period
Large amounts of anaesthetic agent administered
Rapid changes
CV system
HR, pulse, BP
Resp system
Rate and depth of respiration
Depth of anaesthesia
Changes in reflexes
29
Q

What should you do following induction?

A

Endotracheal intubation

Deliver oxygen
Deliver inhalational anaesthetic if required
Protect airway from occlusion or aspiration
Allow ventilation to be supported

Anaesthesia (9 decks)

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