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Anaesthesia > Anaesthetic Circuits > Flashcards

Anaesthetic Circuits Flashcards

1
Q

What should you consider when selecting an anaesthetic circuit?

A
  • correct size for patient
  • minimise airway resistance
  • minimise dead space
  • correct size reservoir bag (approx. 3-6x patient’s tidal volume)
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2
Q

Describe the characteristics of non-rebreathing circuits

A
  • Do not require a CO2 absorbent canister
  • Waste gases are flushed to scavenging
  • Rely on high fresh gas flow to prevent exhaled gases being rebreathed
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3
Q

What are the advantages of non-rebreathing circuits?

A
  • Cheap to buy
  • Simple construction for cleaning and maintenance
  • Soda lime not required
  • Low resistance so ideal for small patients
  • Inspired gas content similar to that on vaporiser
  • Can change level of volatile agent in circuit quickly
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4
Q

What are the disadvantages of non-rebreathing circuits?

A
  • More likely to get pollution
  • Different flow requirements for different circuits
  • Expired moisture and heat is lost
  • High volatile agent consumption rate –> expensive
  • High carrier gas flow required –> expensive!
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5
Q

Name the non-rebreathing circuits

A

Ayres T Piece
Bain
Parallel Lack and Mini Lack
Magill

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6
Q

Describe an Ayres T piece

A
  • Suitable for IPPV
  • Suitable for animals under 8-10kg
  • Suitable for small animals as low resistance
  • relies on high FGF
  • Circuit factor = 2.5-3
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7
Q

Describe a Bain

A
  • Commonly a coaxial system ( one tube inside another)
  • Suitable for animals over 10kg
  • Suitable for IPPV
  • More resistance than Ayres T piece
  • relies on high FGF
  • Circuit factor = 2.5-3
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8
Q

Describe a Magill

A
  • Not commonly used due to lack of practicality (APL valve located at patient end)
  • Suitable for animals over 10kg
  • Reservoir bag is on the inspiratory limb so unsuitable for prolonged IPPV as rebreathing will occur
  • low resistance
  • circuit factor = 1-1.5
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9
Q

Describe the Lack circuits

A
  • Suitable for animals over 10kg
  • May be parallel or coaxial
  • Reservoir bag on inspiratory limb so unsuitable for prolonged IPPV
  • Circuit factor = 1-1.5
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10
Q

Describe the characteristics of Rebreathing circuits

A
  • Closed system
  • Patient rebreathes it’s expired breath once the CO2 has been removed
  • usually the APL valve is semi-closed
  • gases are recycled
  • ALWAYS include a CO2 absorber e.g. soda lime
  • lower FGF - fresh o2 is topped up
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11
Q

What are the advantages of a rebreathing circuit?

A
  • Lower FGF –> cheaper to run
  • Lower volatile agent consumption –> cheaper to run
  • Expired moisture and heat is conserved (less likely to cool patient)
  • less pollution
  • closed or low flow options
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12
Q

What are the disadvantages of a rebreathing circuit?

A

-Expensive to buy
- Soda lime must be replaced regularly when exhausted
- Changes in vaporiser level are slow to change depth of anaesthesia (delay)
- N2O cannot be used safely in closed, low-flow
systems
- higher resistance - unsuitable for small animals/ cats

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13
Q

Name the rebreathing circuits

A

To and Fro

Circle

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14
Q

Describe a To and Fro

A
  • Low flow rates of 0.5-2L/min
  • Not commonly used - the circuit is heavy so can pull out ET tube
  • Contains a CO2 absorbent
  • retains heat well
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15
Q

Describe a Circle

A
  • Suitable for patients over 10-15kg
  • One way valves ensure that gas travels in the right direction
  • high resistance
  • suitable for IPPV
  • High FGF rate for first 10-15 minutes and then reduced and has lower FGF rate than other rebreathing circuits
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16
Q

What is a Humphrey ADE circuit?

A

Can be used a rebreathing or a non-rebreathing circuit - depends on the lever position and the addition of soda lime
- Can be run as a lack or a circle

17
Q

What are the advantages of a Humphrey ADE?

A
  • Can be run at very low flow rates
  • Heat and humidity are preserved
  • Can be used for IPPV
  • For patients 3-100kg
  • Contains a PEEP valve (opens and closes in distinct phases. The valve opens on expiration and only rids unwanted gas)
  • Can attach a ventilator
18
Q

What are the disadvantages of Humphrey ADE?

A

Expensive to buy!

19
Q

What safety checks should be done on anaesthetic circuits?

A
  • correctly assembled?
  • Is the APL valve in the correct position?
  • Are there any kinks, cracks, contamination?
  • Leak test
  • Soda lime exhaustion
  • Scavenge exhaustion

Anaesthesia (15 decks)

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