Exam 2 - Breathing Circuits I (Ericksen) Flashcards
(145 cards)
1
Q
What 6 things does the breathing circuit do?
A
- 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
2
Q
Resistance
When gas passes through a tube where will the pressure be lower/higher?
A
- pressure will be higher @ inlet
- pressure will be lower @ outlet
3
Q
Resistance
The drop in pressure throughout the tube is a measure of what?
What is an example?
A
- measure of the resistance that must be overcome
- ETT w/ flows coming from machine through the circle system delivered to pt - flows will be higher @ the beginning of the system is higher than when it gets to pt
4
Q
What 2 flow types can change resistance?
A
- laminar
- turbulent
5
Q
What happens with resistance when you add length to the system via connectors?
A
- there is more resistance that the system has to overcome
6
Q
What is laminar flow?
A
- flow is smooth and orderly
- particles move parallel to the tube walls
- flow is fastest in center where there is less friction
7
Q
What law is associated w/ laminar flow?
A
Poiseuille’s Law
8
Q
Examples of Laminar Flow
What is “A” demonstrating?
A
Laminar flow - fast in middle/slow @ edges
9
Q
Examples of Laminar Flow
What is “B” demonstrating?
A
- generalized turbulent flow
- particles all bouncing around into each other
10
Q
Examples of Laminar Flow
What is “C” demonstrating?
A
laminar flow initially - then the tube gets narrow & you have turbulent flow
11
Q
Examples of Laminar flow
What is “D,E,&F” demonstrating?
A
- anytime there is decreased diameter, turn, or connection = laminar flow – turbulent flow – back to laminar flow
12
Q
What is turbulent flow?
What are eddies?
A
- flow lines are not parallel
- “eddies”: composed of particles moving across or opposite the general direction of flow
- flow rate is same across diameter of tube
13
Q
Turbulent Flow
What is generalized turbulent flow?
A
- when the flow of gas through a tube exceeds the critical flow rate (when you just have generalized turbulent flow)
- when the critical flow rate is reached - that is when you have turbulent flow
Ex: Tube B in the images
14
Q
Turbulent Flow
What is localized turbulent flow?
A
- gas flow rate below the critical flow rate but encounters constrictions, curves, or valves
- C,D,E, & F are all localized turbulent flow
15
Q
How do you minimize resistance in the breathing circuit/system/gas-conducting pathways?
A
- minimal length
- maximal internal diameter
- be w/o sharp curves or sudden changes in diameter
- ideal to have something short, straight, wide, no curves
16
Q
Does the anesthesia breathing system have minimal resistance?
A
No
* has curved tubes
* elbows
* connectors
* y-piece
* corrugated tubing
* every time we add something to the circle system - we are increasing resistance
17
Q
When does resistance impose a strain on the pt?
A
- when using vent modes where the pt must do part or all of the work
18
Q
Changes in ________ parallel changes in the ________.
A
resistance; work of breathing
* resistance increases = WOB increases
* decreased resistance = WOB decreases
19
Q
What part of the breathing system causes the most resistance?
A
- ETT
- most narrow thing going in the pts airway
20
Q
How can we assess the amount of resistance the pt is experiencing? (4 things)
A
- assess flow-volume loops
- look @ the system
- assess pt breathing
- assess pressure monitors on machine
21
Q
What is compliance?
A
- ratio of change in volume to change in pressure
- how easy something expands/contracts
22
Q
What does compliance measure?
A
Distensibility (mL/cmH2O)
23
Q
What are the most distensible components of the breathing system?
A
- breathing tubes
- reservoir bags
- corrugated tubing
24
Q
What is rebreathing?
A
inhaling previously inspired gases from which CO2 may or may not have been removed
* not just CO2, can be any inhaled anesthetic gases
25
What 3 things is rebreathing influenced by?
1. **fresh gas flow**
-- low flow anesthesia: more rebreathing of gases (sevo, des, iso)
2. **dead space**
3. **breathing system design**
-- semi-closed, open, closed, semi-open
26
# Rebreathing
the amount of rebreathing varies ________ with the total FGF.
inversely
27
What type of FGF anesthesia **does not cause** rebreathing?
**high FGF**
* if vol. of FGF/minute = or is > pt Vm
* as long as exhaled gases are vented out scavenging sytem
28
# Rebreathing
What type of FGF anesthesia **causes rebreathing**?
**low FGF**
* if vol. of FGF/min is < pt Vm
* some of the exhaled gases **must** be rebreathed to make up required volume
29
What is the formula for Vm?
Vm = Vt x RR
**normal 4-6L/min**
30
What is apparatus DS?
**volume in a breathing system occupied by gases that are rebreathed without change in composition**
31
32
What decreases the amount of apparatus DS?
* having an inspiratory & expiratory limb separation as clsoe to the pt as possible (the insp. and exp. limbs are **not** part of DS)
33
What parts of the breathing system make up apparatus DS?
* y-piece
* ETT
* face mask
* anything distal of the y-piece (proximal to the patient/distal from macine)
* **the more we add in b/w the y-piece and everything distal to the y-piece is more apparatus DS**
34
What is physiologic DS?
anatomical and alveolar DS
(Bohr Equation)
35
what is anatomical DS?
* conducting airways
* their job is to add H2O vapor to the gases (acts as humidifier)
36
What is alveolar DS?
* volume of alveoli ventilated but not perfused
* **not adequately participating in gas exchange**
37
What happens to the inspired gas composition when there is not any rebreathing?
* the inspired gas composition is identical to the fresh gas delivered by the anesthesia machine
* **the pt is just getting fresh gas**
38
What happens to the inspired gas composition when there is rebreathing?
* the inspired gas composition is part fresh gas and part rebreathed gas
* **pt is rebreathing everything and also getting some fresh gas at the same time**
39
Does rebreathing cause heat and moisture loss from the pt?
**no**
* it reduces it & acts as a way to conserve heat & moisture
40
What are the effects of rebreathing on inspired gas tensions/partial pressures?
* rebreathing alters inspired gas tensions
* **reduction in the inspired oxygen tension**
* **inhaled induction agents**
-- induction & emergence
* **increased PaCO2**
41
What will happen to partial pressures of CO2 in a hypermetabolic state?
They will increase; esp. if there is re-breathing of CO2
42
What are the 6 desirable characteristics of a breathing circuit?
1. low resistance to gas flow
2. minimal rebreathing
3. removal of CO2 @ rate of production
4. rapid changes in delivered gas when required
-- if turning down gas/over pressurizing = want to be able to see these changes quickly
5. warmed humidification of inspired gas
-- don't want to give dry gases
6. safe disposal of waste gases
-- scrubber/CO2 canisters = scavenging system
43
# Classifications of Circuits
Open
* no reservoir bag
* no rebreathing
* no valves, no tubing
* **ex: n/c, old school drip ether**
* **the pt will breathe in mixture of O2 & RA**
44
# classifications of circuits
Semi-open
* reservoir bag
* no rebreathing
* will have high FGF (> Vm)
* **ex: if Vm is 4L and FGF is 6L = semi-open system**
45
# classifications of circuits
Semi-closed
* reservoir bag
* partial rebreathing
* circle system & valves
46
# Semi-closed circuit
What does the amount of rebreathing w/ a semi-closed circuit depend on?
* when pt is spontaneous breathing
* how open/closed APL is
* exhaustion of CO2 canister
* FGF amount (semi-closed will always be low-flow anesthesia)
47
# Semi-closed circuit
How do we get pressure out of the system w/ a semi-closed circuit?
* squeeze bag, some pressure goes to pt & some goes out scavenging system
* **APL open**: should not have any extra pressure - just intrinsic pressure of pt if mask is intact
* **APL closed**: how we can provide extra pressure to the pt breaths
48
# classifications of circuits
Closed
* reservoir bag
* **complete rebreathing**
-- what comes in circulates and pt rebreathes it
**(depends on FGF)**
-- Vm of 4L/min and FGF is 2L/min = there is rebreathing
-- Vm of 4L/min and FGF is 5L/min = there is not rebreathing
49
When will a closed system have rebreathing?
* if the FGF is = or < Vm
50
What is partial rebreathing?
* a circuit system that allows for a way for gases to escape/be vented off
51
What are the 8 components to the breathing circuit?
1. facemask, LMA, ETT
2. y-piece w/ mask/tube connectors (accordion)
3. breathing tubing
4. respiratory valves
5. reservoir bag
6. A fresh gas inflow site (on the vent)
7. pop-off valve leading to scavenging (APL)
8. CO2 absorption canister
**can also have additional humidifiers, PEEP VALVES, in-line O2 analyzers**
52
What are the basics of the face mask?
* they are clear
* has inflatable or inflated cuff (pneumatic cushion that seals to the face)
* has prongs for attachment to rubber mask holder or head strap
* connects to y-piece or connector (22mm female connection)
53
Where should the facemask fit?
b/w the interpupillary line and in the groove b/w the mental process and alveolar ridge
**should not engulf the whole face or be too small**
54
what is a connector/adaptor?
a fitting that joins together 2 or more components
55
What are the **3 benefits** of connectors/adaptors?
1. extends distance b/w pt and breathing system
-- good if turning HOB away
**could create more DS depending on where connections are**
2. changes angle of conenction
3. allows more flexibility/less kinking
56
What are the disadvantages to adding connectors/adaptors?
* increased reistance
* increases apparatus DS
* additional locations for disconnect (if you start to have problems - assess connections!)
57
Breathing Tubing Basics
1. large bore, corrugated, plastic, expandable
* can distend to increase volume
58
What is the length & internal volume of the breathing tubing?
* 1 meter in length
* 400-500mL/m of length internal volume
58
How is the resistance and flow of the breathing tubing?
* low resistance (distensible)
* flow turbulent d/t corrugation
58
Can 2 breathing tubings be connected?
What would the effect be on DS?
* yes they can
* longer tubes don't increase DS
59
Where is DS located on the breathing tubing?
* from the y-piece to the pt
* d/t unidirectional gas flow
60
What is the reason the inspiratory & expiratory limb are not included in the DS?
* functional unidirectional valves
61
What do we need to perform on the circuit before use?
* pressure check the circuits
* **30cmH2O**
62
What parts of the ETT are DS?
all of it!!
* as long as there is tube in the large conducting airways -- it is DS
62
What should happen w/ the inspiratory & expiratory unidirectional valves during **inspiration**?
* The inspiratory valve should be open
* The expiratory valve should be closed
62
What happens if the inspiratory valve is closed on **inspiration**?
* there will not be forward flow
* the inspiratory limb will become apparatus DS (purple)
63
What should happen with the inspiratory & expiratory unidirectional valves on **expiration**?
* the inspiratory valve should be closed
* the expiratory valve should be opened
64
What happens if the expiratory vlave is closed on **expiration**?
* the expiratory limb will become DS (blue)
65
Where is there bidirectional gas flow?
* areas where there are mixing of inspiratory and expiratory gases
* **this is part of DS & not gas exchange!**
66
What are the unidirectional valves?
What is their main function?
* disks w/ knife edges (thin), rubber flaps, or sleeves
* **function**: direct respiratory gas flow in the correct direction
67
T/F: unidirectional valves have high resistance & low competence.
**false**
* they have LOW resistance & HIGH competence
* they move easily
68
What 2 ways must the valves open & close?
* **open widely w/ little pressure**
-- breathing for infant w/ little pressure
* **close completeley & rapidly w/ no backflow**
-- apparatus DS if the valve gets stuck
69
What is the function of the inspiratory valve?
* opens on inspiration, closes on expiration
* **prevents backflow of exhaled gas**
70
What is the function of the expiratory valve?
* opens on exhalation, closes on inspiration
* **prevents rebreathing**
71
What prevents any part of the circle system from contributing to apparatus DS?
* proper unidirectional valve placement & functioning
72
AGAIN, what parts of the breathing circuit make-up the apparatus DS?
* distal limb of y-connector
* tube/mask
73
Where are the unidirectional valves located on the machine?
* near CO2 absorber canister casing, fresh gas inflow site, and pop-off valve
* they can be mounted anywhere in inspiratory & expiratory limbs
74
What is the flow of gas through the tubing and machine after the pt exhales?
1. exhalation from pt
2. expiratory valve opens & gas goes through
3. gets scrubbed
4. comes back up & bad gas will go through APL if it is open (spontaneous)
5. gas that is cleaned comes back up and catches on w/ FGF
75
What are the 5 requirements for the unidirectional valves?
1. must have arrows/directional words
2. hydrophobic
3. clear dome
4. must open & close appopriately
5. must be placed b/w pt & reservoir bag
-- prevents any of circle system from contributing to apparatus DS
76
What is the breathing/reservoir bag made of? What shape is it?
Non-slipper rubber, plastic, latex
* shape: ellipsoidal for 1 hand ventilation
77
How much volume can the reservoir bags hold?
* 3L for traditional adults
* 0.5-6L range
78
What size is the female connector on the neck of the reservoir bag?
22mm
79
What is the **minimum** pressure the reservoir bag can hold?
30cmH2O
80
What is the **max** pressure the reservoir bag can hold?
* 40-60cmH2O (rubber bags)
* plastic bags have 2x the distending pressure of rubber bags (they can get tight/really big)
81
What are the 5 main functions of the reservoir bag?
1. reservoir for anesthetic gases or O2 (O2 flow helps fill up the bag)
2. means of manual ventilation
3. assistance w/ spontaneous ventilation
4. visual/tactile monitor of ventilation (estimation of vol. of ventilation)
5. protection from excessive positive pressure
82
# Reservoir Bag Function
How can we provide assistance w/ spontaneous ventilation w/ the reservoir bag?
* close the APL a little to help you deliver more or less Vt
* **if APL is open**: harder to give whole Vt
* **combo of bag & APL will help deliver adequate Vt**
83
# Reservoir Bag Function
How can we tell by visual/tactile monitoring what type of breath the pt is taking?
* big/deep breaths: bag collapses & refills quick
* shallow & rapid breaths: bag quivering
-- can open APL a little to allow them to take deeper breath
84
# Reservoir Bag Function
What else can visual/tactile monitoring of the bag tell us?
* can tell if the breathing is matching the vent
* can get good estimate of ventilation based on how much bag is expanding & contracting
85
# Reservoir Bag Function
What happens w/ the extra pressure we are squeezing into the patient?
* some of it goes to the pt
* some of it goes out through the scavenging sytem
* some of it stays in reservoir bag
86
# Reservoir Bag Function
How does the reservoir bag help protect from excess positive pressure?
* the pos. pressures goes to bag and distends more instead of staying in the pts lungs
* if bag was stiff and could not stretch - all that pressure would be in pts airway
87
88
# Reservoir Bag Function
What can we watch on the machine to see how much pressure is being delivered to the patient?
* the mechanical pressure gauges
89
What is the gas inflow site?
* fresh gas inlet
* gases delivered from the common gas outlet to the circuit
90
Where is the gas inflow site located?
near the inspiratory unidirectional valve or CO2 absorbent canister housing in circle systems
91
Where is the preferred location of the **gas inflow site**?
b/w the CO2 absorbent & inspiratory valve
92
# Gas inflow site
What happens w/ the expired gas?
What does the Fresh Gas do?
The expired gas gets scrubbed
* * *
then the fresh gas picks up the clean gas that has been scrubbed & takes it back to the pt via the inspiriatory limb
93
What is the adjustable pressure-limiting valve (APL)?
* pop-off valve
* allows gas to leave the circuit
* **closed = no gas leaving; open = gas leaves**
* dome valve laoded by a spring and screw cap
* user-adjustable
94
What does the APL control?
**pressure in the breathing system**
* tightened screw cap = more pressure required to open it
* it releases gases to scavenging system
95
What are the 3 **APL** Requirements?
* clockwise motion - increases pressure
* counterclockwise motion - decreases pressure
* 1-2 clockwise turns from fully open to fully closed
* an arrow must indicate direction to close valve
96
# APL valve
What is the needle valve?
allows vented gas to go through to the scavenging system
97
# APL valve
What is the Check Valve?
**think of it like the inspiratory/expiratory disc**
* pops up & allows flow to come from the breathing circuit
* depending on how open/closed the needle valve is determines if it will go out the scavenging system
98
# APL use - Spontaneous Respiration
What happens during inspiration & expiration?
**inspiration:**
* the disc (check-valve) is closed
* if we close the APL (needle-valve) partially - it provides CPAP to the patient
**expiration:**
* the disc (check-valve) is open
99
# APL use - assisted/manual ventilation
What happens during inspiration & expiration?
**inspiration:**
* the APL is partially open (we have added some pressure to it)
* assisting the pt w/ breathing
* excess gas is diverted out the scavenging system (more pressure in system = more sent out of scavenging system)
**expiration:**
* the APL is partially open
100
# APL use - assisted/manual ventilation
what is the purpose of having the APL partially open during during assisted/manual ventilation?
* prevents barotrauma
101
# APL use - mechanical ventilation
What happens during inspiration & expiration?
* the APL valve is bypassed & the vent is doing the work
102
# Absorber Canister
What basics do we need to know about the CO2 canisters?
* transparent sides
* single or 2 in a series (stacked)
* remove wrap before use
* they have absorbent
103
# CO2 absorber canister
What is the housing?
* it incorporates valves that close when the canister is removed to prevent gas loss
* **allows us to change it in the middle of a case**
104
# CO2 absorber canister
What is the side/center tube?
* returns the gas to the pt
105
What is the chemical reaction that happens with the CO2 absorbent?
* exothermic reaction
* CO2 + Ca(OH)2 = calcium carbonate
* **when carbonates form - that is when the absorbent turns purple & is exhausted**
106
# CO2 absorbents
What is Soda Lime made of?
* ~80% Calcium hydroxide
* ~5% Sodium hydroxide & potassium hydroxide
* ~15% water
* small amounts of silica & clay - prevents it from hardening/drying out
107
# CO2 absorbents
When is soda lime exhausted?
When all hydroxides become carbonates
108
# CO2 absorbents
How much can Soda Lime absorb?
* 19% of its weight in CO2
* 100g of Soda lime can absorb ~26L of CO2
109
# CO2 absorbents
What is Calcium Hydroxide Lime made of?
What is the other name?
**Amsorb**
* 70% Calcium hydroxide
* 0.7% Calcium chloride
* 0.7% Calcium sulfate
* 0.7% Polyvinylpyrrolidone
* 14.5% water
110
# CO2 Absorbents
What hydroxides were thought to cause compound A?
* NaOH, KOH (strong hydroxides)
* With Sevo in Rodents
111
# CO2 Absorbents
What hydroxide was thought to cause CO production?
* KOH & Desflurane
112
# CO2 Absorbents
What hydroxides cause destruction of inhaled gases?
NaOH, KOH
113
# CO2 Absorbents
Why does Calcium Hydroxide Lime/Amsorb not have NaOH or KOH?
1. Compound A formation
2. CO production
3. Destruction of inhaled gases
114
# CO2 Absorbents
Lithium Hydroxide
* reacts w/ CO2 to form carbonate
* has more CO2 absorbent capacity
* used in submarines & spacecrafts
* can cause burns to skin, eyes, lungs
* **does not react w/ anesthetics** (no KOH/NaOH)
115
# CO2 Absorbents
Litholyme
* lithium chloride catalyst (no reaction w/ inhlaed anesthetics)
* no activators/strong bases (no compound A or CO)
* No regeneration - pH indicators do not become colorless
* lower exothermic reactivity - reduced fire risk, reduced economic/environmental impact
116
# CO2 Absorbents
What is regeneration?
* when you get color change from exhaustion & the color change could revert after time w/ soda lime absorbent
* basically - the pH indicator reverts back colors to white
117
# CO2 Absorbents
What is Spira-Lith?
* anhydrous LiOH powder
* non-granular partially hydrated polymer sheet
* has a larger SA for reaction
* No activators/strong bases (NaOH/KOH)
* reduced temp production
* longer Duration of use
* cost-effective
* **no color indicator**
118
# CO2 Absorbents
How would we know that Spira-Lith is exhausted?
monitor pts inpsired CO2
* If ETCO2 is going up - capnography baseline will be higher (pt. rebreathing)
119
# CO2 Absorbents
Which Absorbents do not contain NaOH or KOH?
1. Amsorb (Calcium hydroxide lime)
2. Litholyme
3. Spiralith
120
# Absorbent Indicators
What is the most common dye?
Ethyl violet
* changes from white - purple
* Can have ethyl orange, cresyl yellow (not as common)
121
# Absorbent Indicators
What happens w/ carbonate formation?
* comes from the exothermic chemical reaction
* pH becomes less alkaline
* color change from white to blue violet
122
# Absorbent Indicators
Around what pH does color change happen?
**10.3**
* fresh absorbent is colorless, pH >10.3
* exhausted absorbent is purple, pH <10.3
123
# Absorbent Indicators
What is bleaching/fading?
* if the absorbent is exposed to really bright fluorescent lighting for a long period - can cause bleaching/fading
* not common in OR now
124
# Absorbent Indicators
Reliability
* can be highly reliable
* Regeneration: turns back white
* Capnometry baseline increasing = rebreathing (change out absorbent)
125
# Absorbent Indicators
What causes drying out of the absorbent?
What is another term for this?
* high gas flows - dries out absorbent that has water
* can lead to compound A & heat in the canister
* **dessication**
126
# CO2 Absorbent
How are the granulars size measured?
**mesh size**
* 4-8 mesh size
127
# CO2 Absorbent
What is the shape of the granulars?
* oddly shaped
* rough, irregular surface
128
# CO2 Absorbent
How much volume of the cannister is gas?
half of the volume of the cannister is gas
129
# CO2 Absorbent
What happens if there is excess liquid water within the canister?
* it decreases the SA & efficiency of CO2 absorption
* the granules get wet and are not going to be able to scrub/absorb the CO2
130
# CO2 canister
What is channeling?
* small passageways that allow gas to flow through low-resistance area
* decreases functional absorptive capacity
131
# CO2 canister
What 5 things can minimize **channeling**?
1. circular baffles (round circular tube)
2. placement for vertical flow
3. permanent mounting (not portable canister)
4. prepackaged cylinders (we don't have to fill them)
5. avoiding overly tight packing (leads to channeling)
132
# Absorbent & anesthetic agent reactions
What is compound A formation?
* decomposition of Sevo
* 2-fluoromethyl-2,2-difluoro-1-(trifluoromethyl) vinyl ether
* can be nephrotoxic in humans (confirmed in rodents)
133
# Absorbent & anesthetic agent reactions
What 4 things lead to **compound A formation**?
1. low FGF
2. increased absorbent temp (overheating itself through reactions)
3. higher inspired sevo concentrations
4. dehydrated (desiccated) absorbent
**NaOH & KOH in combo w/ sevo = compound A formation!!**
134
# Absorbent & anesthetic agent reactions
What causes Carbon Monoxide production?
1. dry absorbent
2. increased temps
3. increased concentrations of anesthetic gases
4. low FGF rates
5. strong base absorbents (KOH, NaOH)
**Des w/ strong hydroxide in presence of dried out absorbent = CO production**
135
# Absorbent & anesthetic agent reactions
At what level of carboxyhemoglobin level will a pulse-ox dip show?
Can IR monitors pick up COHb?
* >35% COHb level = dip in pulse-ox
* IR gas monitor **cannot** pick up COHb
* **co-oximetry picks up COHb**
136
# Absorbent & anesthetic agent reactions
What is the order (greatest - least) of the VA & the risk of CO production?
Desflurane > Enflurane > Isoflurane > Halothane > Sevoflurane
137
# Absorbent heat production
What reaction leads to fires/explosions?
* exothermic reactions
* desiccated strong base (NaOH, KOH) absorbents interacting w/ sevo
138
# Absorbent Heat production
What temp can absorbers exceed?
* 200 degrees C (392 F)
* higher w/ fire in some circuits
139
# Absorbent Heat Production
What 3 things provide the basis for combustion?
1. buildup of high temps
2. flammable degradation productus (formaldehyde, methanol, formic acid)
3. oxygen or nitrous rich gas in the absorber
140
# Absorbent Heat Production
What VA and absorbent should we avoid to reduce the risk of fire?
* Sevo & desiccated strong base absorbent (NaOH, KOH)
141
What are the 6 APSF (anesthesia pt safety foundation) recommendations r/t absorbent?
1. **all gas flows turned off after each case**
-- prevents desiccation
2. **absorbent changed regularly**
3. **change when color change indicates exhaustion**
4. **change all absorbent**
-- 2 canister system: change both!
5. **change absorbsent when uncertain about state of hydration**
6. **using compact canister - change more often**
