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Principles of Science BVetMed 3 > Maintenance of anaesthesia > Flashcards

Maintenance of anaesthesia Flashcards

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1
Q

When can you intubate?

A

Sufficient depth of anaesthesia (eyes rotate ventrally, minimal/sluggish palpebral reflex, loose jaw tone, no swallowing reflex on stimulation) –> Pull tongue out –> laryngoscope on tongue (don’t touch epiglottis or larynx) –> visualise laryngeal opening –> LA and lubricaton

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2
Q

How do you measure an ETT?

A

measure to point of shoulder

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3
Q

What are problems with ETTs? 5

A
  • Occlusions at end - prevented by murphy’s eye
  • Endobronchial intubation
  • Mucus in tube (occulsion and infection)
  • Compression of inside of tube
  • Stretching of tracheal wall
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4
Q

Special considerations - cats and ETTs

A

spray larynx with local anaesthetic (desensitises and reduces laryngospasm). Use intubeaze (lidocaine spray)

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5
Q

List 2 alternatives to ETT in cats

A

V-gel

Laryngeal mask

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6
Q

T/F- mist anaesthetics don’t provide analgesia

A

True (one exception = ketamine). (Analgesia is still required even though patient is unconscious to prevent upregulation of pain processing pathways_.

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7
Q

How can anaesthesia be maintained? 4

A

Inhalational
Intravenous
Combination (injectional and inhalational)
Single IM injection (occasionally)

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8
Q

Define PIVA

A

Partial IntraVenous Anaesthesia

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9
Q

List 4 injectable maintenance anaesthetics

A

Best for TIVA:
Propofol
Alfaxalone

Accumulate so not good for CRI, use for intermittent:
Ketamine
Thiopental

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10
Q

List 6 inhalational maintenance anaesthetics

A 
Isoflurane
Sevoflurane
Halothane
Desflurane
NO2
Xenon
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11
Q

Outline intravenous maintenance

A

TIVA = total intravenous anaesthesia

Intermittent boluses or continuous rate infusion (CRI)

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12
Q

Advantages of intermittent bolus/CRI for maintaining anaesthesia

A

INTERMITTENT: simpler, less equipment, swinging plane of anaesthesia
CRI: target controlled infusion (TCI) possible, minimum infusion rate (MIR)

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13
Q

How are inhalational agents metabolised?

A

Administered and removed from body via lungs (except halothane - liver.
Redistributed to brain and other tissues

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14
Q

How does fat solubility affect inhalational agents?

A

Fat solubility may slow recovery from a long anaesthetic (think vessel rich vs. vessel poor tissues)

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15
Q

What factors affect inhalational agent uptake? 2

A
  • Pressure gradient from vaporiser to brain

- Brain concentration approximates alveolar concentration

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16
Q

What factors affect speed of induction?

A
  • 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 therefore speed of induction/recovery for soluble agents is slower.
17
Q

What is the blood/gas partition coefficient?

A

Number of parts of gas in blood versus alveolus

High number = gas very soluble in blood = slower induction and slower to change depth of anaesthesia during maintenance

18
Q

Define MAC

A

Minimum Alveolar Concentration that is required to prevent movement in response to painful stimulus in 50% animals. For clinical anaesthesia aim for 1.25-1.5 times MAC. Depends on other sedatives/anaesthetics (may cause a MAC sparing effect). MAC values vary between species.

19
Q

List factors that influence MAC and how.

A

Hypothermia (decrease), hyperthermia (increase)
Age - young/old (decrease), young/fit (increase)
Severe hypoxia/hypercapnia (decrease)
Severe hypotension (decrease)
CNS depressant drugs (decrease)
Excitation (increase)
Pregnancy (decrease)

20
Q

Name 3 factors that don’t influence MAC

A

length of anaesthesia
gender
normal blood pH

21
Q

What is the range for normal blood pH?

A

7.35-7.45

22
Q

What is the MAC value in dogs for isoflurane and sevoflurane?

A 
ISOFLURANE = 1.3
SEVOFLURANE = 2.3
23
Q

What is the MAC value in cats for isoflurane and sevoflurane?

A 
ISOFLURANE = 1.6
SEVOFLURANE = 2.6
24
Q

What is the MAC value in horses for isoflurane and sevoflurane?

A 
ISOFLURANE = 1.3
SEVOFLURANE = 2.3
25
Q

Is sevoflurane licensed in dogs, cats and horses?

A

Yes - dogs

No - cats and horses

26
Q

Which anaesthetic reduces CO the most?

A

Halothane - mainly

Also some reduction with iso and sevo

27
Q

T/F: respiratory depression is similar for all anaesthetics

A

True

28
Q

How much metabolism is performed by the liver for differentinhalational anaesthetics?

A

Isolfurane - 0.2%
Sevoflurane - 2%
(Halothane - 20% - the exception)
Desflurane - 0.02%

Predominantly the lung

29
Q

How is sevoflurane metabolised?

A
  • Theoretically free fluoride ions are released (nephrotoxic but no clinically reported problems)
  • Compound A formed during reaction with hot and dry CO2 absorber (nephrotoxic, newer absorbers prevent this)
  • Low flow anaesthesia potentiate these processes
30
Q

T/F: sevoflurane is the best anaesthetic choice for renal disease

A

False (nephrotoxtic free radicals and compound A produced). Isoflurane is a much better option.

31
Q

Compare and contrast isoflurane and sevoflurane

A

ISOFLURANE: vasodilation, CV depression, cheap, stronger smell, patient less compliant, more irritant

SEVOFLURANE: less CVS side effects that iso, maintains better cerebral perfusion than iso, more expensive, better tolerated, less irritant, compound A produced (upon reaction with CO2 absorber)

32
Q

Outline NO2 as an anaesthetic agent

A
  • MAC in animals is 200% –> mist be used with other anaesthetics otherwise risk of hypoxic mistures.
  • Mild analgesic properties
  • very insoluble in blood –> very fast onset
  • can speed onset of another agent (second gas effect)
  • less important now insoluble agents are routinely used
33
Q

What is ‘diffusion hypoxia’ as seen with NO2?

A

at end of anaesthetic, NO2 diffuses rapidly into lungs reducing pp of O2 in the lungs –> therefore to avoid this switch of NO2 15 mins before switching off O2 at end of surgery to prevent this.

34
Q

How does NO2 cause a health risk with chronic exposure or pregnancy?

A

Causes vitamin B12 deficiency (sensory neuropathy, myelopathy and encephalopathy). Also adds to atmospheric greenhouse effect.

35
Q

When should you extubate? What affects this?

A

When swallowing reflex returns (earlier in cats to prevent laryngospams) or later if concerned about airway protection (brachycephalics, vomiting risk and ruminants with risk of regurgitation).

36
Q

What should happen during the recovery period?

A 
Monitoring continues (HR, RR, temp)
\+/- oxygen administration 
\+/- fluids
Temperature (active/passive warming)
Post-op analgesia
Nursing care and TLC - check bladder is empty and bandages are comfortable.

Principles of Science BVetMed 3 (110 decks)

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