Breathing systems Flashcards
What are the two families of breathing systems?
Rebreathing and non-rebreathing
name three functions of a breathing circuit?
- Supply oxygen
- Supply anaesthetic
- Remove carbon dioxide
What are the two ways to remove carbon dioxide?
- via high flow rates e.g. flushed out (no soda lime)
2. via soda lime absorption facilitating lower flow rates.
Name an extra function of the breathing circuit?
Allows you to perform IPPV e.g. squeezing the bag to provide a breath.
What determines the breathing system family?
The way the system gets rid of carbon dioxide.
Which type of system contains soda lime?
Re-breathing system.
What is the advantage of re-breathing systems?
Allows us to use much lower flow rates.
What therefore is a feature of a non-rebreathing system?
Higher flow rates.
What is a disadvantage of non-rebreathing systems?
They are very expensive as they require higher flow rates therefore much more isoflurane.
Name the 5 Non-rebreathing circuits?
1, Maguill (Mapleson A)
- lack
- Mini lack
- Bain (& mini bain)
- T piece
Where is the valve and the bag in Maguill?
The valve is near the patient and the bag is near the machine
What is Maguill efficient for?
Spontaneous breathing
Is Maguill good for IPPV?
No, inefficient for IPPV.
What is the issue with lots of weight being by the animals mouth in Maguill?
can pull the tube out of the animal’s mouth.
What is the MV equation for Maguill?
0.7-1 x MV
What size animal are MV designed for?
Over 10kg - no good for small.
Does Maguill need high or low gas rate?
High to push out carbon dioxide at expiratory pause where the oxygen pushes out the carbon dioxide..
What if there was a rapidly breathing patient with Maguill?
There would not be enough time for the oxygen to remove the carbon dioxide and the animal would re-breath carbon dioxide.
Is Maguill commonly used?
NO -CHEAP AND NASTY!
What is another name for Lack?
Modified Mapleson A
What is Lack efficient for?
Spontaneous breathing
What is it inefficient for?
IPPV, okay for a short while
What kind of circuit is Lack?
Parallel
What is the MV equation for lack?
0.7-1x MV
What size animal is Lack used for?
> 10kg
Why is lack better than Maguill?
Because the valve and the bag are at the same end, away from the patient therefore no weight to pull the tube out of the mouth.
What is the Mini lack known as?
Modified Mapleson
What does lack look like?
Two tubes!
Is there much resistance in a mini lack circuit and why?
minimal resistance because it is smooth bore tubing.
Why do a 1/3 flow rates of mini lack have a T piece?
Saves gas and money and inhalant
What size animal is the mini lack used for?
2-10kg
When is mini lack suitable for long-term IPPV?
When the FGF is increased to 600ml/kg/min
What is the normal flow rate for mini lack circuits?
200ml/kg
Which circuits have a CF of 1?
maguill and lack
Which circuits have a CF of 2-3?
Bain and T piece
What is Bain (&mini bain) otherwise known as?
Mapleson D modified
What does bain look like and which tube supplies gas?
Tube inside a tube and the internal tube supplies the gas.
What is the MV equation of bain?
2.5 x MV
For what sized animals is Bain used for?
7-20kg
What is one of Bains main downfalls?
It requires high flow rates therefore very expensive
Is Bain good for IPPV?
Excellent - lower flow rates can be used for IPPV
When would you use a bain?
If you want to ventilate a patient for a long period of time, not spontaneous breathing.
What is a unique feature of the T piece circuit?
It has no valves
What size animals use T piece?
Under 10kg
Is a T piece high or low resistance?
Low resistance
What is the MV equation for T piece?
2.5 x MV
Is T piece good for IPPV?
Yes, but not easy
What is an easy way to identify the T piece?
There is a paediatric bag used e.g. teddybear
Why has a valve and a bag been added to the T piece?
To make sure you can see when the animal is breathing e.g. draped.
What would you normally assume MV would be?
250ml/kg (0.25L)
How do you calculate flow rates for non-rebreathing systems?
CF x weight x 0.25
How would you work out minute volume normally?
respiratory rate x tidal volume
What is the minute volume?
how much volume you breath in one minute
What is the best way to tell if re-breathing is occuring?
Use a capnograph
For Maguill and lack, what does the reservoir bag contain?
Fresh gas.
For T piece and Bain, what does the reservoir bag contain?
exhaled gas.
Explain then, why the CF for Bain and T piece is higher.
BEcause the circuit factor has to be so high that there is no rebreathing of the resevoir bag in T piece and bain because it contains exhaled gas. The CF of lack and Maguill can be lower because the reservoir bag contains fresh gas.
Name 6 reasons not to use a rebreathing circuit?
- outdated
- dust inhalation
- carbon dioxide channeling
- cubersome
- dead space increases with time
- flow rates the same as circle
If you want to use nitrous oxide, what are the ratios?
2/3 nitrous oxide and 1/3 oxygen
How do we know when the soda lime is exhausted?
Changes colour (white or purple - should say on the packet)
do we use rebreathing circuits commonly?
No, but need to know that they exist.
Name 5 advantages of a circle circuit?
- Efficient
- warm and humidify gas (as re-breathing, good for trachea)
- easy to use
- easy to perform IPPV
- Less pollutant
One disadvantage of a circle circuit?
The soda lime must be changes often
High or low gas flows for circle circuit and why?
Low because the soda lime is getting rid of the carbon dioxide.
What kind of ‘piece’ is on the circle circuit?
Y piece
What is the normal absorbant used for rebreathing circuits?
calcium hydroxide (soda lime and barium hydroxide lime)
What tells you that the soda lime is active?
It generates heat - this can be detected by touching the cannister.
what is produced during re-breathing circuits?
water which can sometimes be seen in the tubes.
in re-breathing circuits, what allows the gas to pass in one direction only?
Pressure generated by the patient’s breathing.
What must be checked prior to use on a circle/ rebreathing circuit?
Valves! if they are sticking, they should be cleaned and dried, or replaced. good practice to keep a new set of valves available.
Which circuit rebreathing circle circuit includes an inspiratory tube inside an expiratory tube?
Universal F circuit
What is the rule about the volume of the breathing bag? what is this usually estimated at?
It must be bigger than the patient’s inspiratory capacity.
This is estimated at 30 ml/kg.
What should the volume of the absorber cannister be?
at least double the tidal volume of the patient for optimum efficiency.
What are our two options when setting the FGF (fresh gas flow rate)?
Closed and semi-closed.
what is the oxygen consumption (ml/min) of a closed system?
10x BW to power of 0.75
Why is a closed system never used?
Because it is impractical and risky!
What does a closed system actually mean?
This means just enough oxygen is delivered to stay alive - this will not be done in a first opinion practice.
Why is nitrous oxide not used in closed system?
Because it will accumulate.
What is the rule in a semi-closed system?
The oxygen flow rate MUST exceed the patient’s oxygen consumption
Where does the excess oxygen go in a semi-closed system?
The extra oxygen is lost via a pressure-release valve.
What are the two stages to closed system fresh gas flow rates?
Initially, need to use both high flow rate and high vaoporiser setting to raise concentration of anaesthetic in circuit.
For maintenance, need both the vapouriser and fresh gas flow rate to be reduced.
What is incredible important in a semi-closed system?
Cannot close the valve entirely else there will be nowhere for the oxygen to escape and the patient will explode.
How do you give the patient a breath in semi-closed circuits?
close the valve and squeeze the bag, then un-screw the valve.
What are the general flow rates used in a semi-closed system for small animals?
flow rate of 2-3 L/min initially and then 500ml to 1L/min during maintenance for dogs
What is the flow rate used for large animals e.g. horses?
Start at 8-10L/min and then reduce
Name 4 advantages of using a circle circuit?
- cheaper (less gases)
- less wastage
- less pollutant
- gases are warmed and humidified (nicer for patients to breath)
In non-rebreathing circuits, how do you change the flow rate?
Assess the response to plain of anaesthesia.
When do you reduce the FGF and % inhalant?
When plane of anaesthesia is stable.
If you want a quick response to anaesthetic, what do you need to change?
Need to change the oxygen flow rate as well. If not, could take 10-15 minutes to respond.
At end of anaesthesia, what do you do with the circuit?
Switch FGF up and inhalant % right down to speed up recovery.
When can nitrous oxide be used? What is the benefit?
In circle re-breathing circuits. (50:50 ratio rather than 2/3 because it accumulates. Might reduce the MAC? Not a lot of benefit.
Name a very expensive type of circle system?
Humphrey ADE circle (combination system)
Name 7 clear advantages of the Humphrey ADE circle system?
- compact, very robust and easy to clean
- versatile 2kg-100kg
- PEEP, IPPV excellent
- low flow rates
- Dogs <10kg (100ml/kg/min)
- Dogs >10kg (1L/min)
- Cats (100ml/kg/min - 600ml/min
- can be used in MRI
What is the disadvantage of the Humphrey ADE circle circuit?
Very expensive!
What is an AMBU?
Artifical Manual Breathing Unit
What do AMBU do and are they essential?
They are self-inflating resuscitators and are essential - they use normal room air or oxygen.
What system is preferred in terms of an induction chamber?
Double box system
Where does the scavenge leave the induction chamber? Why?
From the top. Agent sinks to the bottom therefore if scavenge from the bottom, remving agent before the animal is asleep.
Why do we want to use a small induction chamber?
Less gas used.
How do you work out the Flow rate of Bain and T piece?
BW x 0.5
How do you work out the flow rate of Maguill and Lack?
BW x 1 x 0.25
