Breathing circuits Flashcards by Adrie McFarland

What are the 4 classifications of breathing circuits?

open
semi open
semi closed
closed

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What is considered an open breathing circuit?

Non-contained system where the patient exchanges gas with the atmosphere

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What is considered a semi-open breathing circuit?

FGF > patients minute ventilation

*There is no rebreathing of exhaled gas

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What is considered a semi closed breathing circuit?

FGF is < the patients minute ventilation. Allows rebreathing of exhaled gas. Unidirectional valves increase airway resistance.

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What is considered a closed breathing circuit?

Uses a very low FGF

There is complete rebreathing of exhaled gases

The volumes of inspired and expired gases are equally matched, gas does not exit the scavenger.

*The change in gas concentration is very slow due to a very low FGF

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Relationship b/w FGF and minute ventilation in semi-open circuit. Example?

FGF exceeds minute ventilation

Using a 10L/min flow during anesthetic induction

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Relationship b/w FGF and minute ventilation in semi-closed circuit. Example?

FGF is less than minute ventilation

Reducing FGF to 2 L/min after tracheal intubation

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Relationship b/w FGF and minute ventilation in closed circiut

FGF is just enough to support the patients oxygen consumption

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How does the reservoir bag help to decrease FGF needed?

Exhaled gas accumulates in there, which is then given back to the patient to rebreathe making it possible to decrease FGF needed

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How many L can an adult reservoir bag hold

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What are the limits for max pressure of reservoir bag set by american society of testing and materials?

The 3 L bag should not exceed an internal pressure of 60 cmH2O if the bag is inflated up to 4 times its size.

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Where does gas go when the pressure inside the circuit exceeds the pressure set by the APL valve?

To the scavenging system

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At what point is the APL bypassed?

When the vent is on

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What is the most common site of circuit disconnect?

Y piece

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Where does dead space usually begin and end

Begins at the y piece and ends at the terminal bronchioles.

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What can increase dead space while a y piece is in use

Anything that is added between the patient and the y piece such as an HME

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What are 2 common conditions that increase inspired carbon dioxide?

Incompetent unidirectional valve. Whichever of the 2 becomes incompetent will lead to dead space. *Pt will rebreathe CO2
CO2 absorbent exhaustion

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What can you do if the CO2 absorbent exhausts during a procedure?

Change the absorbent quickly

Convert a closed or semi-closed circuit to a semi-open circuit by increasing the FGF to 5-8 L/min

What caution do you have to take if you switch your CO2 absorbent out during a case?

Have a back up plan in place in case you cannot get the new absorbent to seat correctly!

If you see that your patient is rebreathing but you increase your FGF and it doesn’t fix the problem, what is likely the issue?

Unidirectional valve is probably incompetant

How many configurations of the Mapleson circuits are there?

A-F

Generally speaking, what components are present in the mapleson circuits? Which circuit is the one exception to these general items?

Reservoir bag
Fresh gas inlet
Corrugated circuit tubing
APL valve
Mask

*Mapleson E does not contain an APL valve or reservoir bag

Generally speaking, what components are NOT present in the mapleson circuits?

Unidirectional valves
CO2 absorber

Where is the fresh gas inlet compared to the patient for each mapleson circuit? Are there any exceptions?

Near the patient for all except A-which it is near the bag

Where is the APL location compared to the patient for each mapleson circuit? Are there any exceptions?

A-C: Near the patient D: Away from the patient E: Not present F: Tail of the bag

Which maplesons have corrugated tubing? Which do not?

All except C

Which maplesons have reservoir bag? Which do not?

All have bag except E

Should FGF be high or low when using Mapleson circuits?

HIGH! The patient will exhale then whatever gas is in the tubing will be washed out by a high FGF.

Rebreathing using a Mapleson circuit is minimized with a higher or lower FGF? Bigger or smaller Vt? Shorter or longer expiratory time?

Higher Smaller Vt Longer expiratory time

What is the best kind of monitoring method to determine the amount of FGF required to prevent rebreathing?

ETCO2

What are the best Mapleson to be used with spontaneous ventilation?

Best: Mapleson A (A >DFE> CB) All Dogs Bite Worst: Mapleson B

What are the best Mapleson to be used with controlled ventilation?

Best: Mapleson D (DFE > BC > A) Dont be Arrogant Worst: Mapleson A

Generally speaking, how many more times higher should the FGF be than the Minute Ventilation to prevent rebreathing?

~2.5 x

The Bain system is a modified which Mapleson?

Where does FGF enter the Bain system?

thin inner tubing

Where does exhaled gas exit the Bain

Outer corrugated tubing

How does incoming fresh gas get warmed and humidified in Bain system

By exhaled gas

Is Bain used for spontaneous or mechanical ventilation?

Either

What should FGF be compares to minute ventilation when using a Bain?

~2.5x minute ventilation

What happens if the inner tubing of the Bain becomes kinked or disconnected?

This situation converts all of the corrugated tubing to dead space, putting the patient at risk for hypercarbia

What is the PETHICK test?

Performed as part of the pre-anesthetic check out when using a Bain

PETHICK test result that indicates the circuit is safe to use. Not safe to use?

Safe to use if reservoir bag collapses Not safe to use if the reservoir bag remains inflated

How to perform PETHICK test with Bain?

Occlude the elbow at the patient end of the circuit Close the APL Use the O2 flush valve to fill the circuit Remove the occlusion at the elbow while flushing the circuit