Breathing systems Flashcards
What system is this?
T piece
What system is this?
What system is this?
Magill
What system is this?
Parallel lack
What system is this?
Circle
Which systems can you IPPV on?
Think ABC (Airways, breathing, circulation)
i.e. Ayres T-piece (0-10kg) (System factor 2.5-3)
Bain (10-18kg) (System factor 2.5-3)
Circle (10kg+)
Pros/cons of Lack/Magill?
(+) = low curcuit factor (1-1.5)
(+) = can be used from large range (10-35kg)
(-) = cannot IPPV
Pros/cons of rebreathing systems (which ones are rebreathing)?
Circle (+ Humpreys ADE)
(+) = lower FGF –> economical
(+) = reduced heat and moisture loss
(+) = reduced environmental pollution and waste
(+) = can IPPV
(+/-) = used in animals >10kg
(-) = Percentage of inspired inhalant anaesthetic agent often differs from the vaporiser setting and changes in percentage can be slow.
(-) = Higher resistance than nonrebreathing system
How to calculate the FGF?
NB: not for circle
FGF = system factor x minute volume
Minute volume = the volume of expired gas in a minte
MV (mls/minute) = tidal volume x respiratory rate.
OR
Minute volume = 200mls/kg/min.
How to calculate gas flow for rebreathing systems (i.e. _____)?
Circle systems:
Initial high rate = ~2-3L/min –> denitrogenation + increase the concentration of inhalant in the system
After this the minimum FGF rate is = animals metabolic oxygen demand of 10mls/kg/minute
BUT, in practice the circuit is run with the valve open to allow excess gas to escape and the flow rate is set to exceed the metabolic oxygen demand. Generally a setting of 1L/min is used for small animals up to 100kg.
A 9 month old female cat has been brought to the surgery to be neutered. She weighs 3.2kg. What breathing system(s) would be the most appropriate for this case?
T Piece
Low resistance as is small patient.
FGF = minute volume x 2 to 3
minute volume = 200mL/kg/min
= 200 x 3.2
= 640mL/min
FGF = 640 x 2 to 3 = 1.28 to 1.92L/min
Mini-Lack
FGF = 1 x minute volume
= 640mL/min
N.B. 640mL may be difficult to set on the flowmeter so set the FGF to 1L/min
A 55kg Newfoundland has a dental booked at the practice. What breathing system(s) would be the most appropriate for this case?
Circle
Rebreathing system, allows lower fresh gas flow so is more economical
Metabolic O2 consumption estimate = 10mL/kg/min
Metabolic O2 demand = 10 x 55kg = 550mL/min
A minimum FGF to 1L/min is usually used for a circle in practice
15kg Springer Spaniel is set to have a thoracotomy. What breathing system(s) would be the most appropriate for this case?
Will need IPPV as thorax will be open
Bain
Can use for patients 10-20kg.
– Minute volume = 200mL/kg/min = 200 x 15 = 3L/min
– FGF = minute volume x 2 to 3
= 3L x 2 to 3
= 6 to 9L/min
Circle
Rebreathing system, allows lower fresh gas flow so is more economical
Metabolic O2 demand estimate = 10mL/kg/min
Metabolic O2 demand = 10 x 15kg
= 150mL/min
N.B. Usually a circle FGF is set to a minimum of 1L/min
A 9.2kg Whippet is coming in for a digit amputation. What breathing system(s) would be the most appropriate for this case?
Bain, Circle, Lack or Magill
Whippets tend to have a large lung capacity in comparison to body weight and so would be able to cope with resistance of a breathing system when other dogs of the same weight might not.
