Breathing systems Flashcards
Desirable Characteristics of A Breathing Circuit
Low resistance to gas flow
Minimal rebreathing
Removal of CO2 at rate of production
Rapid changes in delivered gas when required
Warmed humidification of inspired gas
Safe disposal of waste gases
No reservoir bag and no rebreathing circuits
Open
nasal cannula, open drop ether
no valves or tubing.
systems have no valves, no tubing: for example open drop ether, or a nasal cannula. In either, the patient has access to atmospheric gases.
Reservoir bag but no rebreathing circuits
Semi-open
(no rebreathing, high fresh gas flow [higher than minute ventilation])
Reservoir bag and partial rebreathing circuits
Semi-closed
(some rebreathing occurs, FGF andAPL settings at intermediate values)
Reservoir bag and complete rebreathing circuits
Closed
Depends on FGF
(fresh gas inflow exactly equal to patient uptake, complete rebreathing after carbon dioxide absorbed, andAPL closed)
Circle systems
closed, semi closed, semi open
Mask requirements
inflatable (Pneumatic cushion that seals to face)
clear
Proper mask fit size/position
Fits between the interpupillary line and in the groove between the mental process and the alveolar ridge
Masks connect to…..
Connect to the Y-piece or connector with a 22 mm female connection
A fitting that joins together 2 or more components
Connectors/Adapters
Benefits of connectors/adapters
Extends distance between patient and breathing system
Change angle of connection
Allow more flexibility/less kinking
Disadvantages of connectors/ adapters
Increased resistance
Increases dead space
Additional locations for disconnects
Breathing Tubing length and internal volume
1 meter in length
Internal volume - 400-500 mL/m of length (makes distensible)
Breathing tubing air flow is always_______
Flow always turbulent due to corrugation
Places for bidirectional gas flow
lma, y piece
Dead space only from
Dead space only from Y piece to patient d/t unidirectional gas flow
Breathing tubing pressure check using….
Pressure check circuits before use
Hold pressure at 30 cm H2O
Unidirectional valves disks eith____
Disks with knife edges, rubber flaps, or sleeves
Direct respiratory gas flow in the correct direction
unidirectional Valves
Unidirectional valves have _____ resistance and ______ competence
Low resistance and high competence
Failure for unidirectional valves to seal causes a large amount of the circuit to become _______
appartatus dead space
Opens on inspiration and closes on exhalation
Prevents backflow of exhaled gas
Inspiratory valve
Opens on exhalation and closes on inspiration
Prevents rebreathing
Expiratory valve
What is Apparatus dead space
Distal limb of the Y-connector
Tube/mask
Proper valve placement and functioning prevents any part of the circle system from contributing to _______
apparatus dead space
Unidirectional Valves are located near ________
Valves are located near CO2 absorber canister casing, fresh gas inflow site, and the pop-off valve
Unidirectional valves requirements
Arrows or directional words
Hydrophobic
Must open and close appropriately
Clear dome
Must be placed between pt and reservoir bag
Breathing/Reservoir Bags volume
3L traditional for adults
0.5 - 6L
Breathing/Reservoir Bags must have _____ connector on the neck
Must have 22 mm female connector on neck
Breathing / reservoir bags minimum and max pressure
Minimum pressure 30 cm H2O
Max pressure 40 - 60 cm H2O (rubber bags)
Breathing/Reservoir Plastic Bags vs Rubber bags
Plastic bags – 2x the distending pressure of rubber bags
Reservoir bag shape
Ellipsoidal for 1 hand ventilation
Permits gas to leave the circuit. Controls pressure in breathing system
Adjustable Pressure-Limiting Valve (APL)
Tightened screw cap, more gas pressure is required to open it
Gases are delivered from the common gas outlet to the circuit.
Gas Inflow Site
APL valve other name
Pop-off valve
Gas Inflow Site located______
Located near the inspiratory unidirectional valve or CO2 absorbent canister housing in circle systems
Gas Inflow Site preferred location
between CO2 absorbent and inspiratory valve
Other locations for other circuits depends on whether breathing is spontaneous, assisted, or controlled because the type of breathing influences the efficiency of carbon dioxide elimination.
A reservoir function is necessary because _____
anesthesia machines cannot provide the peak inspiratory gas flow needed during normal spontaneous inspiration solely from fresh gas flow.
APL releases gas to_____
Releases gases to scavenging system
Adjustable Pressure-Limiting Valve (APL) adds ____ during spontaneous ventilation or pressure-limited controlled respiration
PEEP
APL rotation requirements
Clockwise motion increases pressure (closes valve)
Opposite motion decreases pressure (opens valve)
1-2 clockwise turns from fully open to fully closed
An arrow must indicate direction to close valve
incorporates valves that closes when the canister is removed to prevent gas loss
housing for absorber canister
What does the Side/center tube in an absorber canister do?
returns the gas to the pt
Soda lime components
Calcium hydroxide (~80%)
Sodium hydroxide and potassium hydroxide (~5%)
Water (~15%)
Small amounts of silica and clay
Soda lime activators/ strong bases
Sodium hydroxide and potassium hydroxide (~5%)
Soda lime is exhausted when……
all hydroxides become carbonates
Soda lime chemical reaction
CO2 + Ca(OH)2 = CaCO3 + H2O + heat
Soda lime absorbents can absorb _______ in CO2
19% of its weight in CO2
100 g can of sodal lime can absorb approximately ______ CO2
26L
Calcium hydroxide lime components
Calcium hydroxide (70%)
Calcium chloride (0.7%)
Calcium sulfate (0.7%)
Polyvinylpyrrolidone (0.7%)
Water (14.5%)
Another name for Calcium hydroxide lime and benefits
ansorb
decrease productions of; compounds A and CO and Destruction of inhaled gases
APL releases gas to_____
Releases gases to scavenging system
Adjustable Pressure-Limiting Valve (APL) adds ____ during spontaneous ventilation or pressure-limited controlled respiration
PEEP
Absorbent that Reacts with CO2 to form carbonate
lithium hydroxide
More CO2 absorption capacity
absorbents used in Used in submarines and spacecrafts
lithium hydroxide
Absorbent with No activators/strong bases
Litholyme
Does not form compound A and CO
reaction with inhaled anesthetic agents
absorbent with pH indicators do not become colorless
litholyme
No regeneration
pH indicators do not become colorless
Absorbent with Lower exothermic reactivity, reduced risk of fire, and reduced economic/environmental impact
Litholyme
Absorbent with Anhydrous LiOH powder within a nongranular partially hydrated polymer sheet
Spira-Lith
Spira-Lith features
-Larger surface area for reaction
-No activators/strong bases
-Reduced temperature production
-Longer duration of use
-Cost-effective
-No color indicator
What is the most common dye for absorbent indicators
Ethyl violet is the most common dye
Ethyl orange, cresyl yellow
Absorbent Indicators Undergoes color change around pH
pH of 10.3
Absorbent Indicators Carbonate formation
pH becomes less alkaline
White to blue violet
Fresh absorbent is_____ and is at a pH_____
Fresh absorbent is colorless, pH > 10.3
Exhausted absorbent is _____, pH ______
Exhausted absorbent is purple, pH < 10.3
Gold standard for Absorbent Indicators reliability
capnometry
Regeneration- Color fading
Half volume of absorbant cannister is _____
gas
mesh size
4-8
Excess liquid water within the absorbent canister decreases
Excess liquid water within canister decreases surface area and efficiency of CO2 absorption
Small passage ways allowing gas to flow through low-resistance areas
channeling in co2 absorber
Decreases functional absorptive capacity
channeling Minimized by
Circular baffles
Placement for vertical flow
Permanent mounting
Prepackaged cylinders
Avoiding overly tight packing
Compound A name
2-fluoromethyl-2,2-difluoro-1-(trifluoromethyl) vinyl ether
Low FGF, Increased absorbent temperature, Higher inspired sevoflurane concentrations, and Dehydrated absorbent causes what?
Compound A formation
Rank inhalants highest to lowest levels of CO formation
Desflurane ≥ enflurane > isoflurane»_space; halothane = sevoflurane
Carboxyhemoglobin levels >________
levels >35%
Pulse ox or IR gas monitors wont pick it up
Risk of formation of CO with______
Increased temperatures
Increased concentrations of anesthetic gases
Low FGF rates
Smaller pt size
Strong base absorbents
APL releases gas to_____
Releases gases to scavenging system
Adjustable Pressure-Limiting Valve (APL) adds ____ during spontaneous ventilation or pressure-limited controlled respiration
PEEP
Exothermic reactions, leading to fires and explosions
Absorbent Heat Production
Baralyme, anhydrous LiOH risk
Desiccated strong base absorbents interact with sevoflurane
Absorbers exceed 200 degrees Celsius (392 degrees Fahrenheit) and higher w/ fire in some breathing circuits
What in absorbers can cause combustion
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
Avoid sevoflurane use with desiccated strong base absorbents
components of Mapleson circuits
Reservoir bag
Corrugated tubing
APL valve
Fresh gas inlet
Patient connection
What does the mapleson circuit not hve?
CO2 absorber
Unidirectional valves
Separate inspiratory and expiratory limbs
Other name for mapleson circuit
Also called, carbon dioxide washout circuits or flow-controlled breathing systems
Because there is no clear separation of inspired and expired gases with maleson circuits, rebreathing will occur when the ________.
inspiratory flow exceeds the fresh gas flow.
Best efficiency of all systems for spontaneous ventilation, worst during controlled ventilation
Mapleson A (Magill’s system)
Rebreathing with magills system during controlled ventilation occurs unless __________
minute ventilation is very high, more than 20L/min
why is Mapleson B innefficient
Much of FGF is vented through APL during exhalation
FGF should be 2x minute volume during spontaneous and controlled ventilation to prevent rebreathing
Identical to Mapleson B except corrugated tubing omitted, Almost as efficient as Mapleson A
Mapleson C
The circuit used for emergency resuscitation
Mapleson C
FGF 2x minute volume
Most efficient system for controlled ventilation
Mapleson D
Mapleson D fgf
FGF 2 – 2.5x minute ventilation
APL valve in use of Mapleson D
Spontaneous ventilation: Open (excess gases are vented out during expiration)
Manually controlled ventilation: Partially closed (pressure rises during inspiration due to squeezing of bag and excess gases are vented out)
Mechanically controlled ventilation: Closed (excess gases are vented through the ventilator spill valve).
Corrugated tubing attached to the T-piece forms reservoir
No reservoir bag/No APL
Mapleson E (Ayre’s T-Piece)
preferred in pediatric patients for both the spontaneous and controlled ventilation
Mapleson E
used in less than 20kg pts
Due to absence of APL valve, the resistance in the system is lower compared to other systems and are preferred in pediatric patients for both the spontaneous and controlled ventilation.
Jackson-Rees modification (of Mapleson E)
Mapleson F (Jackson Rees)
Reservoir bag added
Mapleson F Minute ventilation
2 - 2.5x minute ventilation
Excessive pressure less likely to develop
No APL valve
Improved rebreathing with maplesons efficiency is d/t_______
location of the pop-off valve relative to FGF
system with significant amounts of fresh gas is vented through pop-off at end expiration
B&C mapleson systems
systems FGF drives exhaled alveolar gas away from pt
DEF systems
Spont ventilation mapleson efficiency ranking
Mapleson A is greater than Maplesons DFE, which are greater than Maplesons CB
Controlled vent mapleson efficiency ranking
Maplesons DFE are greater than Maplesons BC, which are greater than Mapleson A
Advantages of Maplesons
Simple, inexpensive, and lightweight
Changes in FGF composition result in rapid changes in the circuit
Low resistance to gas flow
No toxic products d/t lack of CO2 absorbent
No degradation w/ VAs
Disadvantages of Maplesons
Require high FGF
Conservation of heat and humidity low in inspired gas
Scavenging challenging
Not suitable for patients with MH
Systems with the Exception to scavenging challenges
Except Mapleson D, APL valve away from pt
Rules to prevent rebreathing with circle systems
-Unidirectional valve must be located between the pt and the reservoir bag on both the inspiratory and expiratory limbs
-The fresh gas inflow cannot enter thecircuitbetween the expiratory valve and the pt
-APL valve cannot be located between the pt and the inspiratory valve
Partial rebreathing occurs but some waste flow is vented through APL or waste gas valve of ventilator
Circle System Function Semi-closed
FGF is less than minute ventilation
low-flow anesthesia
50% of expired gas is rebreathed after CO2 removal
Higher FGF with minimal rebreathing and more venting of waste gas
Circle System; Semi-open
post-op and ICU vents, scuba gear
Rate of oxygen inflow exactly matches metabolic demand
Circle system; closed
Rebreathing is complete
No waste gas is vented
VAs are added to circuit in liquid form in precise amounts or through the vaporizer
Low- and minimal-flow anesthesia
Advantages of low - flow anesthesia
decreased use of VAs
improved temp and humidity control
reduced environmental pollution
Disadvantages of low flow anesthesia
-Difficulty in rapidly adjusting anesthetic depth
-Possibility of accumulating unwanted exhaled gases ( ex: CO, acetone, methane)
-VA degradation by-products (ex: CO, compound A)
Advantages of circle system
-Low FGF can be used
-Elimination of CO2
-Relatively stable inspired gas concentration
-Conservation of moisture/heat/gases
-Prevention of OR pollution
Disadvantages of circle systems
-Complex design
-CO or compound A
May compromise Vt during controlled ventilation
-ASA Closed Claims Project; Misconnections/ disconnections
Components of self- inflating manual resuscitators
-Self-expanding Bag
-T-shaped non-rebreathing Valve
-Bag Inlet Valve
-Pop-off valve
-Excess oxygen venting valve
-Oxygen reservoir
Uses of self inflating manual resiscitators
Hand ventilation in the absence of an oxygen or air source
Pt transport
CPR
Emergency back-up
Hazards with self inflating manual resiscitators
Barotrauma or gastric insufflation
Significant variation of tidal volume, PIP, and PEEP
Nonrebreathing valves generate resistance
Effective preventing contamination anesthesia machine from airborne diseases
Bacterial Filters
Bacterial filters are placed on_____
Placed on the expiratory limb
Amount of water vapor in a gas
Humidity
Mass of water vapor present in gas in mg H2O/L of gas
Absolute humidity
Percent saturation; amount of water vapor at a particular temp
Relative Humidity
Pressure exerted by water vapor in a gas mixture
Water Vapor Pressure
Maximal contact of inspired gas w/ large mucosal surface area in the _______
nasal cavity
Heating and humidification has occurred by ______
mid trachea
mid trachea temperature
34°C with an absolute humidity of 34 to 38 mg/L (95% to 100% relative humidity)
Absolute humidity of air at body temperature
Absolute humidity of 44 mg/L (100% relative humidity)
Isothermic saturation boundary
Cold ambient temperatures
Little capacity to hold water vapor
Low absolute humidity
Upper airway transfers large amounts of heat and moisture
Little heat energy is expended to warm inspired gases
Warm ambient temperatures
Cool inspired gas may trigger ______
bronchospasms
Damage that under humification has on the respiratory tract
Secretions thicken
Ciliary function decreases
Surfactant activity is impaired
Mucosa susceptible to injury
Condensation of water in the airway causes…..
-Reduced mucosal viscosity and risk of water intoxication
-Inefficient mucociliary transport
-Airway resistance, risk of pulmonary infection, surfactant dilution, atelectasis, and V/Q mismatch
-Obstruction to sensors
HME filter is placed______
Placed close to the pt, between Y piece and proximal end of ETT or LMA
HME physiologic changes
Low ETCO2 reading
Increases resistance and dead space in circuit
Efficiency may be reduced with large Vt(Hydrophobic models)
Paper or other fiber barrier coated with moisture-retaining chemicals
Hygroscopic HME
May have some electrostatic properties
Filter Most efficient retaining heat and moisture
Hygroscopic HME
Effects of hygroscopic HME becoming saturated
Increased inspiratory/expiratory resistance
Reduced heat and moisture retention efficiency
Filter with Pleated hydrophobic membrane with small pores
Hydrophobic HME
More efficient filters of pathogens
Hydrophobic HME
Where are humidifiers placed
Placed in inspiratory limb downstream of unidirectional valve
Heated humidifiers should not be placed in expiratory limb
Condensation from humidifier can cause what physiologic change?
Condensation can decrease delivered Vt
type of active humidifier that work by passing the fresh gas flow down a tube through a water reservoir causing the gas to “bubble.” Water vapor is absorbed as the bubbles pass through the reservoir
Bubble humidifiers
work by passing gas over a heated water reservoir. There are two variants: one that utilizes a wick and one that utilizes a hydrophobic membrane.
Passover humidifiers
-Water is heated outside the vaporizer in counter flow humidifiers. After the water is heated, it is pumped to the top of the humidifier where it enters small diameter pores and runs down a large surface area. Gas, flowing in the opposite direction, is warmed and humidified to body temperature.
Counter-flow humidifiers
utilize a plastic capsule which injects water vapor and heat directly into the inspiratory limb of the ventilator circuit just before the patient y-piece.
Inline vaporizer humidifiers
Unheated humidifier cannot deliver more than
They cannot deliver more than about 9 mg H2O/L.
Most unheated humidifiers are disposable, bubble-through devices that are used to increase the humidity in oxygen supplied to patients via a face mask or nasal cannula
Advantages of humidifiers
Can deliver saturated gas at body temp or higher
More effective than HME
Disadvantages of humidifiers
Bulky
Potential electrical, fire hazards
Contamination, cleaning issues
Higher cost than HME
Do not offer more protection against heat loss compared to forced air warming
