Breathing Systems Flashcards
FGF
Fresh gas flow: the total volume of gas that flows from the anaesthetic machine into the breathing system per minute.
This includes oxygen, nitrous oxide and any other gases employed.
TV
Tidal volume
MV
Minute volume
SF
System factor
IPPV
Intermittent positive pressure ventilation. Might be required if the patient stops breathing due to reaction, cardiopulmonary arrest etc.
APL valve
Adjustable pressure limiting valve
RR
respiratory rate
Give some examples of non-rebreathing systems
- T-piece
- Lack or Mini Lack
- Bain
- (Humphrey ADE in smaller patients)
Give some examples of rebreathing circuits
- Circle
- Humphrey ADE (for larger patients)
- Induction chamber
What are some characteristics of a Bain breathing system?
- Tube within a tube
- Non-rebreathing
- Can be used for IPPV
- Suitable for 10-30kg patients
- Relies on high FGF
What are some characteristics of the T-piece breathing system?
- One long tube and one short tube. The expiratory limb (short) has the reservoir bag on.
- Non-rebreathing
- Can be used for IPPV
- Good for small patients <10kg and fine for tiny patients (500g)
- Relies on high FGF
What are some characteristics of the Lack or Mini Lack breathing system?
- 2 parallel tubes. Can recycle dead space gas for the patient.
- Non-rebreathing.
- Cannot be used for IPPV.
- Can potentially give the odd breath, but not prolonged IPPV as the patient would be breathing in CO2.
- Lack = patients >10kg
- Mini Lack = patients 2-10kg
- More oxygen efficient than T-piece and Bain due to lower SF
What are some characteristics of the Circle breathing system?
- Soda lime used to absorb CO2 (must be changed regularly)
- Rebreathing
- Can be used for IPPV, but not at the low flow rates used for maintenance
- Standard circle = patients 10-150kg
- Pediatric tubing = patients 2-10kg
- Common in practice and very oxygen efficient (after initial high FGF)
- Warms and humidifies the gas entering the patient
What are some characteristics of the Humphrey ADE breathing system?
- Designed for use out in the field where one system does all.
- Rare.
- Rebreathing for larger patients or can be non-rebreathing for smaller patients.
- Can be used in an MRI.
- Low FGF rates so economical with oxygen.
Give some characteristics of an induction chamber as a breathing system?
- Rebreathing
- Can reduce stress of handling, but can cause stress if used inappropriately
- Can dry out patient’s eyes.
- Health and safety concern when opening lid.
- Cannot be used for IPPV.
Which breathing system is shown here?
Circle
Which breathing system is shown here?
Humphrey ADE
Which breathing system is shown here?
Bain
Which breathing system is shown here?
Lack or Mini Lack
Which breathing system is shown here?
T-piece
How do you calculate the FGF required for a patient on a non-rebreathing system?
FGF = MV x SF
MV = TV x RR
TV = 10mls/kg
How do you calculate the FGF required for a patient on a rebreathing system?
First 10-15 mins = 100mls/kg/min
Maintenance = 10ml/kg/min
How do you calculate patient TV?
TV = 10mls/kg
How do you calculate the size of the reservoir bag needed for a patient on a rebreathing system?
Reservoir bag = TV x 4
Why do we need a high FGF initially on a rebreathing system?
- To cause denitrogenation
- To flood them with anaesthetic agent so this can take over the job of the induction agent
Should your APL valve be open or closed when you connect the patient to the breathing system?
Open
The image shows what happens if it is closed - there is not way for exhaled gas/fresh gas to leave the breathing system when pressure gets too high
The reservoir bag mimics what is happening to the patient’s lungs
Should the APL valve be open or closed when you give a breath via IPPV?
Closed.
Close the valve → squeeze the bag (be mindful of patient size) → open the valve
