Circuits Flashcards
What connects the anaesthetic machine to the patient?
An ET tube
What is the APL valve?
a safety feature
Will open once a high pressure is reached in the circuit
What are the calculations for FGF?
Tidal volume = BW X 10-25ml
Minute volume = TV X respiratory rate
Fresh gas flow = MV X circuit factor
FGF units = ml/min or L/min
How do you choose the right circuit?
aim to tailor circuit size to patient
minimise airway resistance
minimise dead space
Choose correct reservoir body
Give the properties of non-rebreathing circuits
do not require a CO2 absorbent canister
waster CO2 and waster inhalational gases are flushed to scavenging system
These circuits rely on a high FGF to flush exhaled gases from the circuit so they cant be rebreathed by patient
Give properties of Ayres T-piece circuit
Suitable fo ranimals under 10kg simple system with low resisitenace FGF passes down trespiraotry limb reservoir baf on expiratory limb - suitable for IPPV Used in a variety of configurations RElies on a high FGF therefore Circuit factor = 2.5-3
Give the properties of the Bain circuit
Suitable for animals over 10kg
Commonly seen as coaxial system - always check inner tubing in place
Reservoir bag on expiratory limb as for T-piece
Has an APL valve
Suitable for IPPV
Circuit factor 2.5-3
Give properties of the lack circuit
Suitable for animals over 10kg
(mini lack may be used for smaller animals)
May be parallel or coaxial
Reservoir bag on inspiratory limb - not suitable for IPPV long term
Unlike the magill the APL valve is located close to the anaesthetic machine
Circuit factor = 1-1.5
Give advantages of non-rebreathing circuits
Cheap to buy
Simple construction for cleaning and maintenance
Soda lime is not required
Low resistance
Inspired gas content similar to that on vaporiser
Can change level of volatile agent in circuit quickly
Give disadvantages on non-rebreathing circuits
High carrier gas flow required therefore expensive
High volatile agent consumption rate therefore expensive
Expired moisture and heat is lost
There are different flow requirements for different circuits
Give properties of rebreathing circuits
Operates as closed (usually valve is semi-closed) systems
The animal re-inhales its expired breath once CO2 has been removed
Give properties of circle circuit
Suitable for animals over 10kg
Complex system with APL valve semi-open (difficult to calibrate at low levels)
Initally use higher flow rates for 10-15min to allow denitrogenation then 10ml/kg.min
Describe soda lime
colour change to indicate which varies between manufacturer
Canisters should be inspected before each procedure and at the end of the day for signs of exhausation
Wear gloves when changing canister
Always chack canister for leaks
What are advantages if rebreathing systems?
lower fresh gas flow rates requires = cheaper to run
lower volatile agent consumption = cheaper to run
Expired moisture and hea is conserved
less pollution than othe systems
closed or low flow options
What are the disadvantages of rebreathing systems?
Higher resistance
Expensive to buy
Soda lime must be replaced regularly when exhauseted
Changes in vaporaiser levels are slow to change depth of anaesthesia
N2O cants be used safely in closed low flow systems
