Anaesthetic circuits and airway monitoring Flashcards
what are some factors of choosing a circuit?
- resistance
-controlled versus spontaneous respiration - fresh gas flow requirements
- inclusion of nitrous oxide
- mechanical dead space
- circuit drag
- ease of maintenance and sterilisation
what is a non rebreathing circuit?
- no co2 absorption or one way valves
- need a high fresh gas flow
- quick changes to volatile agent
- requires use of circuit factor calculation
what are some examples of non-rebreathing circuits?
- lack
- mini lack
- bain
- ayres t-piece
- humphrey ADE system
what is a lack and mini lack circuit?
- reservoir bag on inspiratory arm
- circuit factor of 1-1.5
- not suitable for long term IPPV
what is a Ayres T-piece and Bain?
- reservoir bag on expiratory arm
- circuit factor 2.5-3
- can be used for long term IPPV
what are some advantages of a non-rebreathing system?
- low resistance so suitable for small mammals and birds
- simple and inexpensive to buy
- no requirement for soda lime
- inspired anaesthetic concentration. can be easily and quickly adjusted
what are some disadvantages of a non-rebreathing system?
- high oxygen requirements
- high anaesthetic agent requirements
- require knowledge of flow rate calculation
- lose heat and moisture in expired air (use HME)
what is a rebreathing system?
- allow exhaled gases to be reused after the CO2 has been removed
- contain one way valves and co2 absorbent
- economical when used as a closed system as lower oxygen flow need
- reduce heat loss as warm air breathed in
- altering amount of agent takes time
what are some advantages of rebreathing system?
- low gas flow requirements
- low volatile agent use
- expired moisture and heat is conserved
what are some disadvantages of rebreathing system?
- high resistance
- expensive to purchase
- regular replacement of soda lime needed
- canister may be source of gas leak
what does APL valve mean?
- adjustable pressure lifting valve
- prevents high pressures building up inside the circuit by opening when the pressure reaches a certain point allowing gas out but not air in
what is the expiratory pause?
where no gas is being inhaled or exhaled by the patient but gas continues to flow into the circuit from the machine
what is the ayres t-piece?
- can be used on patients less than 8kg
- circuit has low resistance and minimal dead space
- reservoir bag is on the expiratory limb
- APL valve on expiratory limb
- can be used for IPPV
- circuit factor 2.5-3
what is a parallel lack?
- used on patients weighing over 10kg
- two gas carrying tubes running alongside or parallel to each other (one for fresh, one for waste)
- reservoir bag is on the inspiratory limb
- circuit factor 1-1.5
what is a mini-lack?
- narrow tubing (less dead space)
- suitable for patients up to 10kg
- circuit factor 1-1.5
what is a bain?
- coaxial
- used in patients over 10kg
- high fresh gas flow over 15kg
- can be used for long term IPPV
- circuit factor 2.5-3
what is humphreys ADE?
- able to switch between different modalities
- lack-like arrangement for spontaneous breathing
- bain for when patients need ventilation
- soda lime turns it into a re-breathing
what is a magill?
- valve close to patients head
- circuit factor 1-1.5
patients over 10kg
what is a circle?
- rebreathing
- needs a reservoir bag, sodalime canister and APL valve
- initial high levels of o2
- metabolic demand = 10ml/kg
what is the calculation of fresh gas flow?
FGF = minute volume x circuit factor
what is the calculation for minute volume?
MV = tidal volume x RR
what is the calculation for tidal volume?
TV = 10/15 x BW
what is co2 absorbent?
- comprises of calcium hydroxide, sodium hydroxide and water
- granualar particles absorb co2 and change pH - colour change
what is a supraglottic device?
- creates a seal over the pharynx
- does not enter the trachea
- expensive
