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Flashcards in Anaesthetic Circuits Deck (32)
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What is the other name for a closed and semi-closed circuit

Closed - usually re-breathing

Semi-Closed - non-rebreathing


What is the function of the APL valve

Safety feature
Will open once a high pressure is reached in the circuit


How do you choose the correct reservoir bag?

Should be roughly 3-6 x patients tidal volume (VT)


What factors should you consider when choosing the right circuit

aim to tailor the circuit size to the patient
Minimise airway resistance
Minimise deadspace
Choose correct reservoir bag size


Name 2 points about non-rebreathing circuits

1. Do not require a CO2 absorbent canister
2. Waste CO2 and waste inhalational gases are flushed to scavenging system
3. Rely on high pressure gas flow to flush exhaled gases from the circuit so they cannot be rebreathed by the patient


What is the circuit factor for ayres T-piece and Bane



How does the ayres T-piece inspiration work:

 Patient inhales FGF coming down the inspiratory limb from the anaesthetic machine


How does ayres T-piece expiration work:

o Expiration
 Patient breathes out waste gases which are flushed down the expiratory limb by the high FGF eventually leaving via the APL valve (if a paediatric modification) to scavenge
 Two parts of expiration:
• 1. Dead space gas that hasn’t participated in gas exchange therefore not a lot of CO2 and does not contain volatile agent
• 2. Voiding of waste gases and will include large amounts of CO2
o Expiratory pause
 Tubing fills with fresh gas


What weight is suitable for Ayres T-piece?

under 8-10kg


What weight is suitable for bain circuit?

over 10kg


What kind of system is a bain seen as?

Coaxial system. Tip: Always check inner tubing is in palce


How does bain inspiration works?

 Fresh gas flow from the machine travels up the inner tube. When the animal breathes in it takes fresh gas from the inner tube plus gas from the outer expiratory limb.


How does the bain expiration work?

o Expiration
 Exhaled gases are forced up the expiratory outer tube
• Some do pass into the inner limb where they mix with fresh gas
o Expiratory pause
 Incoming fresh gas flushes any exhaled gas through the inner tubing and out of the circuit. therefore high fresh gas flow is required as this prevents the patient rebreathing exhaled gases


What is the circuit factor for a lack and magill?



What weight is a lack and mini lack suitable for?

Lack - over 10kg
Mini-lack - under 10kg


How does the inspiration on a lack work?

 Gases inhaled from inspiratory limb and reservoir bag


How does expiration on a lack work?

 Dead space gases pass back down the inspiratory limb
 Second portion of inspiration is flushed out of expiratory limb by the fresh gas flow
 Long term IPPV with this circuit will disrupt gas flow and cause rebreathing at conventional FGF rates


Name two advantages of a non-rebreathing circuit

- Cheap to buy
- Simple construction for cleaning and maintenance
- Soda lime is not required
- Low resistance
o Ideal for smaller patients
- Inspired gas content similar to that on vaporiser
- Can change level of volatile agent in circuit quickly


Name 2 disadvantages for non-rebreathing circuits

- High carrier gas flow required therefore more expensive
- High volatile agent consumption rate therefore expensive
- Expired moisture and heat is lost
- There are different flow requirements for different circuits
- More likely to get pollution with these circuits


What do rebreathing circuits always include that non-rebreathing circuits do not?

CO2 absorber


When is a circle circuit suitable?

for animals over 10-15kg


Does the circle circuit have high or low resistance?



What flow rate should be run for a circle circuit?

nitially use higher flow rates for 10-15 minutes to allow de-nitrogenation then 10ml/kg/min


What indicates soda lime is exhausted?

Colour change either pink to white, or white to purple


When should soda lime cannisters be checked and when should it be changed

before each procedure and at end of day
Change when 2/3 or more is exhausted


What checks for soda lime cannisters should you always follow

always wear gloves when changing the canister
Always check cannisters for leaks


Name 2 advantages of rebreathing systems

- Lower fresh gas flow required
o Cheaper to run
- Lower volatile agent consumption
o Cheaper to run
- Expired moisture and heat is conserved
o Not a constant cold fresh gas flow
o Healthier for respiratory tract
o Stop them dropping temperature
- Less pollution than other systems
- Closed for low-flow options


Name 2 disadvantages of rebreathing systems:

- Higher resistance
- Expensive to buy
- Soda lime must be replaced regularly when exhausted
- Changes in vaporiser level are slow to change depth of anaesthesia
- N2O cannot be used safely in closed low flow systems
- Cannot be used on cat
o Can’t push air around
- Expensive to buy
o But arguably you save in the long run


How can a humphrey ADE be used

either as a rebreathing or non-rebreathing circuit depending on lever position and additional of soda lime


What weight does Humphrey ADE claim to be useful for