Exam 2 Breathing Systems: Part 1 (6/20/24) Flashcards
Six Definitions of a Breathing System:
- Receives gas mixture from the machine
- Delivers gas to the patient
- Removes CO2
- Provides heating and humidification of the gas mixture
- Allows spontaneous, assisted, or controlled respiration
- Provides gas sampling, measures airway pressure, and monitors volume
When gas is passing through a tube, where will the pressure be the highest?
the pressure at the inlet will be higher than at the outlet
Describe Laminar Flow
Flow is smooth and orderly
Particles move parallel to the tube walls
Flow is fastest in the center where there is less friction
True or False:
In laminar flow, the flow rate is the same across the diameter of the tube?
FALSE!
Flow is fastest in the center where there is less friction
Which Law is used to describe Laminar Flow?
Poiseuille’s Law
What type of flow is this?
Laminar Flow
What type of flow?
Localized Turbulent Flow
What type of flow is this?
Localized Turbulent Flow
What type of flow is this?
Generalized Turbulent Flow
What is the name given if the particles are moving across or opposite the general direction of flow ?
“Eddies”
Turbulent Flow
In turbulent flow, is the flow rate the same or does it differ across the diameter of the tube?
Flow rate is same across diameter of tube
Describe Generalized Turbulent Flow:
When the flow of gas through a tube exceeds the critical flow rate
Describe Localized Turbulent Flow
Gas flow rate below the critical flow rate but encounters constrictions, curves, or valves
To minimize resistance, gas-conducting pathways should have ___
- minimal length
- maximal internal diameter
- be without sharp curves or sudden changes in diameter
Changes in resistance ___ changes in the work of breathing
Parallel
What is one example of something that causes more resistance than the breathing system?
ET Tube
What is compliance?
What does it measure? (Unit?)
Ratio of the change in volume over the change in pressure.
Measures Distensibility (ml/cm H2O)
What are the most distensible components of our breathing system?
Breathing Tubes (Corrugated Tubing)
Reservoir Bags
Compliance can help determine the patient’s ___.
Tidal Volume
To inhale previously inspired gases from which CO2 may or may not have been removed:
Rebreathing
What is Rebreathing influenced by?
- Fresh gas flow (High vs Low)
- Dead space
- Breathing system design (Semi, Closed, Open)
Amount of rebreathing varies ___ with the ___.
Inversely
total FGF
Will rebreathing occur or not?
Patient’s Minute ventilation is 5L/min and the FGF is 6L/min:
NO! The FGF is greater than the patient’s minute volume.
So long as exhaled gas is vented (not a closed system)
Will rebreathing occur or not?
Patient’s Minute ventilation is 6L/min and the FGF is 6L/min:
NO! The FGF is equal to the patient’s minute volume.
So long as exhaled gas is vented (not a closed system)
Will rebreathing occur or not?
Patient’s Minute ventilation is 6L/min and the FGF is 4L/min:
YES! The patient’s minute volume is greater than the FGF rate.
Will rebreathing occur or not?
Patient’s tidal volume is 600 mls and has a respiratory rate of 10 breaths per minute. The FGF is at 5L/min.
YES! The patient’s minute volume is greater than the FGF rate.
Minute volume = Vt (RR per min)
True or False:
Some of the exhaled gases must be rebreathed to make up required volume
TRUE
Define Apparatus Dead Space:
Examples?
Volume in a breathing system occupied by gases that are rebreathed without change in composition
Ex: ETT, Face Mask, anything distal to Y-Piece
How can we decrease the amount of Apparatus Dead space?
by having inspiratory and expiratory limb separation as close to patient as possible
Summation of anatomical and alveolar dead spaces equals…
Physiologic Dead Space
Define Anatomical Dead space:
amount in the conducting airways; adds H2O vapor
2 Things that rebreathing reduces:
- Heat loss
- Moisture loss
Six desirable characteristics of a Breathing Circuit:
- Low resistance to gas flow
- Minimal Rebreathing
- Removal of CO2 at the same rate of production
- Rapid changes in delivered gas when required
- Warmed humidification of inspired gas
- Safe disposal of waste gases
Describe an Open Circuit:
Example?
No reservoir bag and no rebreathing.
Ex. Nasal Cannula
Patient’s minute ventilation is 4L/min and the FGF is 6L/min, what kind of circuit are we likely dealing with?
Semi-Open:
Reservoir bag but no rebreathing.
Describe a Semi-Closed circuit:
Reservoir bag and partial rebreathing
In a closed circuit, if the FGF is equal or less than the patient’s minute ventilation, what will occur?
Rebreathing
A pop-off valve leading to the ____ is a required component to a breathing circuit.
scavenging system
Where (in great detail) should the mask fit on a patient’s face?
Between the interpupillary line and in the groove between the mental process and the alveolar ridge
Benefits to using connectors/adapters:
- Extends distance between patient and breathing system
- Change angle of connection
- Allow more flexibility/less kinking
Disadvantages to using connectors/adapters:
- Increased resistance
- Increases dead space
- Additional locations for disconnects
Which of the following is NOT used to describe the breathing tubing?
A. Large Bore
B. High Resistance
C. Corrugated
D. Plastic
E. Expandable
B. High Resistance
The breathing tubing should have low resistance and be somewhat distensible.
Length and internal volume of breathing tubing:
1 meter in length
400-500 ml/m
How is the flow through the breathing tubing classified?
Why?
Flow is always turbulent due to the corrugation!
Generally, does adding longer tubes increase dead space?
Why or why not?
NO! Dead space is only from the Y piece to patient and not in the tubing itself because of the unidirectional gas flow valves.
Is there ever an example in which the tubes could increase/contribute to dead space?
Yes, If the unidirectional Valves are closed/not working, they CAN contribute to dead space
If the unidirectional valves are unable to close completely and rapidly with no backflow, what can occur?
An increase in Apparatus dead space
The inspiratory unidirectional valve prevents:
The expiratory unidirectional valve prevents:
Inspiratory: Prevents backflow of exhaled gas
Expiratory: Prevents rebreathing
Although the unidirectional valves can be mounted anywhere between the inspiratory and expiratory limbs, these are the typical places in which they are located:
- CO2 Absorber canister casing
- Fresh gas inflow site
- Pop-off valve
5 requirements for the unidirectional valves:
- Arrows or directional words
- Hydrophobic
- Must open and close appropriately
- Clear dome
- Must be placed between pt and reservoir bag
Traditionally the reservoir bags are ___ for adults but can range from ___ to ___.
3L
0.5L - 6L
Minimum and Maximum pressures for the breathing/reservoir bags.
Min: 30 cm H2O
Max: 40-60 cm H2O
Describe the distending pressure difference between plastic bags and rubber bags:
Plastic bags have 2x the distending pressure as the rubber bags
Describe some of the functions of the reservoir bag:
- Reservoir for anesthetic gas and O2
- A way to manual ventilate
- Assists with spontaneous ventilation
- Protection from excessive positive pressure
Another name for the Gas inflow site is:
Fresh gas inlet
Preferred location of the gas inflow site:
between CO2 absorbent and inspiratory valve
The ___ permits gas to leave the circuit.
APL Valve or Pop-off valve
Turning the APL valve in a clockwise motion will do what?
Increase the pressure
How many clockwise turns does it take to fully close the APL valve if it is fully open?
1-2
When is the APL valve open, closed or partially closed during spontaneous respiration?
Closed during Inspiration
Open during Expiration
Partially closed during inspiration with CPAP
The APL valve will be partially open during both inspiration and expiration during what type of ventilation?
Assisted/Manual Ventilation
APL use during mechanical ventilation?
Completely bypassed during both inspiration and expiration.
Prior to using an absorber canister we need to make sure to…
Remove the wrap!!
If we are needing to change out the absorber in the middle of a case, are we able to do that? Or do we have to wait until the end of the procedure?
You can change it in the middle of the case if necessary. The housing of the absorber incorporates valves that close when the canister is removed to prevent gas loss.
What is the purpose of the side/center tube located in the absorbent cannister?
Returns the gas to the patient
What kind of reaction occurs that causes our CO2 absorbers to become exhausted?
Exothermic Chemical reaction
Once exhausted, Carbonates are formed
Describe the components of soda lime:
- Calcium hydroxide (~80%)
- Sodium hydroxide and potassium hydroxide (~5%)
- Water (~15%)
- Small amounts of silica and clay
When does the soda lime become exhausted?
when all hydroxides become carbonates
Which components of the soda lime absorbent was thought to cause compound A and carbon monoxide?
Potassium and Sodium hydroxide
Sevo: Compound A / Des: Carbon Monoxide
Soda lime can absorb ___ of its weight in ___.
19%
CO2
100 g of Soda lime can absorb about ___.
26 L of CO2
Which absorbent excludes both K and Na hydroxide in its makeup?
Calcium hydroxide lime (Amsorb)
Where is the Lithium hydroxide absorbent used?
Submarines and Spacecrafts
This absorbent does not have “regeneration”
What does this mean?
Litholyme
This means the pH indicators will not revert back to being colorless after becoming exhausted. (Soda lime has regeneration)
Describe the Spira-Lith absorbent:
- Non-granular
- Larger surface area
- Reduced temperature production
- Longer Duration of use
- No color indicator
Because the spira-lith has no color indicator, how would we know it is becoming exhausted?
Capnography
The patient’s baseline would continue to rise over time
Which dye is the most common absorbent indicator?
Ethyl Violet
As carbonates are forming, what color change occurs?
White to a blu-ish violet
At what pH does the absorbent undergo the color change?
around 10.3 and below
What is the purpose of the mesh located in CO₂ absorbents?
Maximize absorption and minimize resistance
Channeling is when there are small passage-ways that allow gas to:
What does channeling decrease?
Flow through-low-resistance areas
Channeling decreases functional absorptive capacity
Channeling can be minimized by:
- Circular baffles
- Placement for vertical flow
- Permanent mounting
- Prepackaged cylinders
- Avoiding overly tight packing
Which of the following pictures is an example of channeling?
Compound A formation theoretically occurs with these 4 things:
- Low FGF
- Increased absorbent temperature
- Higher inspired sevoflurane concentrations
- Dehydrated absorbent
Desiccated strong base absorbents interact with ___.
Sevoflurane
Select All that Apply:
A buildup of these 3 flammable degradation products within the absorber provide a basis for combustion.
A. Formaldehyde
B. Sulfuric Acid
C. Methanol
D. Polyvinylpyrrolidone
E. Silica
F. Formic Acid
A. Formaldehyde
C. Methanol
F. Formic Acid
Rationale: Buildup of high temperatures, flammable degradation products (formaldehyde, methanol, and formic acid), and oxygen or nitrous rich gases w/in the absorber all provide basis for combustion
With which anesthetic gas was carbon monoxide most commonly occuring?
Desflurane
Per the APSF recommendations, if we are using a 2 canister system…
Change them both
True or False:
Compact canisters do not need as frequent changing as regular canisters.
FALSE
