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160 Cards in this Set
- Front
- Back
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Compliance
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Change in volume/change in pressure
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4 imperative features of an anesthesia ventilator
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1. Deliver gases from the machine to the alveoli in the same concentration as set in the shortest possible time
2. Effectively eliminate CO2 3. Have minimal apparatus dead space 4. Have low resistance |
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Example of open anesthesia circuit
Semi open? |
open drop anesthesia system
Mapelson system with high fresh gas flow, circle system with high fresh gas flow, Self-inflating ambu bag, scuba systems |
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Exampe of semi-closed anesthesia circuit?
Closed? |
Circle system with low fresh gas flow
Circle system with apl/pop off valve closed, no fresh gas except physiologic O2 |
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Features that make a breathing system open
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No reservoir, no rebreathing, CO2 released into atmosphere
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Features that make a breathing system semi-open
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Reservoir present, but no rebreathing
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Downsides of semi-open systems
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Require high fresh gas flows (approx 3x expired tidal volume), do not conserve heat or humidity, fresh gas flows need constant adjustment, difficult to include valves and they must be positioned close to the patient
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Dead space within lung:
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Ventilated but non-perfused areas (such as when PE occludes circulatory flow, even though that portion of lung still fills with air, no gas exchange takes place)
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Dead space within airways
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Everything above the level of the alveoli (mouth, nose, trachea, bronchioles, terminal bronchioles)
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Where does the dead space begin in the circle system?
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At the junction or elbow where the inspiratory and expiratory limbs meet
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What are the features that distinguish a semi-closed anesthesia system?
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Reservoir present, partial rebreathing
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Parts of the circle system
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Inspiratory limb with unidirectional valve, expiratory limb with unidirectional valve, reservoir bag, carbon dioxide absorber, FGF inflow site, pop-off valve for venting excess gas
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What would happen if you put an adult on a pediatric ventilator circuit?
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Tidal volume would be poorly matched to size of ventilator tubing, creating resistance. Difficult to deliver gases, very difficult for patient to breath spontaneously (high resistance), and coughing or bucking into circuit would not buffer or absorb any of the pressure generated
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What would happen if you put a child onto an adult circuit?
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Any changes to the delivery of gases would take forever to take effect
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Features of a closed anesthesia system
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Reservoir, complete rebreathing (circle system with apl/pop-off valve closed and only physiologic o2 supplied); CO2 must be scrubbed and O2 supply must perfectly match the patient's oxygen consumption
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downside of a closed anesthesia system
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Changes take a very long time to take effect due to low flows, there is little margin of error for O2 delivery
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Absolute humidity
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Mass of water vapor in a given volume of air
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Relative humidity
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Actual vapor pressure/ saturated (or possible) vapor pressure x 100
Relative humidity is affected by temperature. (for example, it only gets foggy on cool mornings) |
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Does relative humidity increase or decrease as temperature falls?
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Increases
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Dew point
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Temperature at which water molecules begin to stick together
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Why does dew form?
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At lower temperatures, air has a reduced capacity to contain water vapor, so the vapor condenses into liquid form and deposits on the ground
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The partial pressure of saturated water vapor at 37 degrees celsius (physiologic temp) is:
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47 mm Hg
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At what point, when breathing through the nose, does air reach 100% relative humidity?
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By the time it reaches the trachea, air is completely saturated with water vapor
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What is the length of standard breathing circuit tubing?
Diameter? |
1 meter
22 mm |
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What is a built in safety feature designed to prevent connection of the breathing circuit to the scavenger?
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Different diameter tubing
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Why is ventilator tubing corrugated?
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To allow flexibility and prevent kinking
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Is gas flow through circuit tubing laminar or turbulent?
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Turbulent
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Inspiratory valve
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opens on inspiration, closes on expiration, opens widely and closes quickly, prevents rebreathing CO2
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Shape of valves on anesthesia circuits
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Dome shaped
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Respiratory valves must be located
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Between the patient and the reservoir bag in each limb of the circuit
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Available sizes of reservoir bags?
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0.5, 1, 2, and 3 L sizes
(standards set for pressures generated when inflated up to 4 times normal size) |
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Functions of reservoir bags
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Provide means for manual ventilation, give rough estimate of tidal volume, serve as reservoir for gases
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What is the purpose/function of pop-off/ APL valves?
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Allows gas to leave the circuit
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How many turns does it take to either fully open or fully close the APL valve?
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1-2 full turns- clockwise to close, counter clockwise to open
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In partial rebreathing or non-rebreathing systems, where does CO2 go?
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Vented to the atmosphere/room
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What are the end products of conversion of CO2 using soda lyme or baralyme?
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Water, heat, and calcium carbonate
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What color does soda lyme turn when exhausted?
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Purple
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When what percent of soda lyme has changed color should you change it?
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50-70% (in two canister system, when top canister's color has fully changed and second canister is beginning to turn
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Where does the color in soda lyme come from?
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organic dyes
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What happens to exhausted soda lyme when allowed to rest?
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It very partially regenerates and the color converts to white, but it is still exhausted
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What volume of fresh gas flow will ensure that CO2 is removed?
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At least 1.5L
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What would you do if your CO2 absorber became used up in the middle of the case?
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Turn the circle system into a semi-open system by increasing the fresh gas flow to the point that the patient is not rebreathing any CO2 (entire tidal volume is fresh gas)
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Mesh size for CO2 absorbant: how is it figured and what is the most common
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How many granules can fit into a 1 inch mesh (1/x inches)
4-8 is most common |
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What is the up side of small granule size? The down side?
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Surface area versus resistance/channeling
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What are the main constituents of most CO2 absorbents? Which absorbent does not contain the two major ingredients in other absorbents?
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Sodium hydroxide and potassium hydroxide; Amsorb is Calcium Hydroxide based and does not contain sodium or potassium hydroxide (but is more expensive)
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What are the major steps and byproducts in the chemical conversion of CO2 with NaOH or KOH?
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Water + CO2 = carbonic acid (h2CO3) (first neutralization reaction)
H2CO3 + sodium or potassium hydroxide = na2co3 (Sodium carbonate) + HEAT + H20 then converts to CaCo3 (calcium carbonate) + NaOH (second neutralization + reactivation of absorbent take place) |
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Carbon Monoxide production in process of CO2 conversion: biggest culprits? Under what conditions is it most likely to happen?
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Desflurane> Isoflurane> sevoflurane= halothane
Worse with dry absorbent and with baralyme versus soda lyme |
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Why do you need consider amount of time you can administer sevoflurane with soda lyme absorbent??
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sevo is unstable in soda lyme, and produces Compound A in rats, which is nephrotoxic
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What is the maximum amount of time you can administer Sevoflurane with soda lime at flows of 1-2 lpm?
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2 MAC hours
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How do you calculate MAC hours?
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concentration of agent that will put 50% of people to sleep = 1 mac; different concentration for different agent; convert % running into MAC, then multiply x hours running at that concentration
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How many MAC hours can you run sevoflurane at 1-2 lpm? Give an example of 1 combination that would give you this number of MAC hours
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2 MAC hours at 1-2 lpm fresh gas flow. (for example, 1% for 4 hours = .5 MAC x 4 hours = 2 MAC hours)
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Recommended rate of fresh gas flow for sevoflurane
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greater than 2lpm
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Never run sevoflurane at fresh gas flow rates:
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less than 1 lpm
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MAC of sevoflurane
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2%
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Volatile that is biggest culprit of CO production
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Desflurane
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Which produces more toxic effects: desflurane or sevoflurane
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Comparable rates of toxicity despite CO production (desflurane) and Compound A production (sevo)
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Size particles that bacterial filters will catch
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1 micrometer
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Bacterial filters go where on the circuit?
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Expiratory limb
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ASTM standards require that all ventilators have a ___ alarm
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Loss of main power supply alarm
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Mechanism on most modern ventilators that avoids pressure and volume build up in patients lungs due to fresh gas flow:
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decoupling devices
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What compresses the bellows?
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Force of compressed oxygen (or air)
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Pressure limiting (or safety relief) valve
What pressure does this valve usually pop-off at? |
Prevents the ventilator from continuing to deliver breath if high pressures are encountered (i.e. if the patient coughs during inspiration); limits driving gas pressure
65-80 cm H20 |
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Spill Valve
Is this valve open or closed during inspiration? |
Vents excess exhaled gas into scavenging;
Closed during inspiration |
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When does the spill valve open?
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During late expiration (after exhaled patient gas has had a chance to fill bellows)
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What is the purpose of fresh gas decoupling? How does the ventilator accomplish this?
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Fresh Gas decoupling prevents accumulation of excess tidal volume in patient's lungs. Ventilator compares exhaled tidal volume filling bellows (including fresh gas flow) to set tidal volume, and downregulates the next tidal volume accordingly (i.e. subtracts fresh gas flow from tidal volume);
decoupling valve diverts fresh gas flow to reservoir bag |
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exhaust valve
Open or closed during inspiration? |
Vents drive gas into atmosphere (or scavenging) during exhalation
Closed during inspiration |
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Most modern ventilators use ___ bellows:
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Ascending (fill and ascend on exhalation, descend on inspiration)
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potential risk of descending bellows
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Masks leaks, will still fill if patient becomes disconnected from circuit
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What do ASTM standards dictate about vaporizers?
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Vaporizers must be concentration calibrated, located within the fresh gas circuit, vapor concentration must be provided by specific gas calibrated controls and knobs
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Vapor
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Gas phase of a liquid substance at room temperature
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Modern vaporizers
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Concentration calibrated variable bypass
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Volumes Percent
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The number of units of a volume of gas out of the total of 100 units of total gas volume; Percentage of total gas
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Latent heat of vaporization
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Amount of energy (number of calories) it takes to convert 1 gm of liquid to vapor
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Specific Heat
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Heat required to raise 1 gm of substance 1 degree celsius
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Specific heat of anesthetic agents determines
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amount of heat required to maintain a stable temperature following vaporization
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The higher the specific heat, the ____ the agent will exchange heat
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slower
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Thermal conductivity
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The speed at which heat moves though a substance; the higher the conductivity, the better it conducts heat
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Vaporizers are composed of _____ conductive materials
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Highly
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Thermal stabilization
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The process of making something capable of withstanding changes in environmental temperature
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Rapid temperature changes in vaporizers are prevented by:
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Constructing vaporizers out of heavy metals that act as heat reservoirs
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What is one way that vaporizers accommodate changes in temperature
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Bi-metallic strip- composed of two metals with differing amounts of conductivity- it bends one way or the other based on temperature-
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How does the bimetallic strip work
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It It bends one way with increased temperatures to allow more gas to flow over the top and bypass the volatile liquid, thus decreasing the amount of vapor picked up. In cold temperatures, it bends the other direction and directs more fresh gas down through the volatiles and therefore increases the amount of vapor it picks up. (variable bypass)
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What are some ways that variable bypass vaporizers increase the surface area that produces vapor?
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Baffles and wicks
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What are three types of vaporizers (how they create vapor, not models)
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Flow over, bubble through, injection
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Modern vaporizers are:
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Flow over, variable bypass, concentration calibrated, temperature compensated, agent specific, out of circuit
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Vaporizers are calibrated at_____ :
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Sea level
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At high altitude, vaporizer output will be:
Below sea level, vaporizer output will be: |
Increased (low boiling point agents are more sensitive to change in atmospheric (and therefore partial pressure) change than high boiling point agents)
Decreased (due to resistance to flow) |
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Vaporizers are calibrated with which gas?
What is the effect of using other gases in fresh gas flow? |
Air or Oxygen
If calibrated in air, O2 use will result in increased output, and N2O will result in decreased output due to solubility differences |
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What is the pumping effect?
Does it result in increased or decreased vaporizer output? |
Intermittent back pressure created by positive pressure ventilation (seen at low flows)
Increases |
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What safeguards are in place to prevent pumping effect?
What safeguards to prevent pressurizing effect? |
Check valve between vaporizer outlet and common gas outlet; reason for negative pressure check on machine checkout, other features that prevent this are small vaporizer chambers and tortuous vaporizer outflow path
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What is the pressurizing effect?
Does it result in increased or decreased vaporizer output? |
Caused by intermittent inspiratory high pressures (at high flows)
Decreased |
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When is the pumping effect most likely to occur?
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Low FGF, large pressure fluctuations, low vaporizer settings
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Vaporizers must be capable of accepting flows of:
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15 lpm
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Where would you find information relating to the effects of conditions of use (ambient temperature changes, back pressure effect, input flow rates)?
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The operator's manual
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Vaporizer standard:
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Isolation of vaporizers from each other must be provided
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What is the ventilator standard for the maximum amount of vapor that can be delivered with the vaporizer in the off position?
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<0.1%
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Vaporizer standard: vaporizer concentration can only be increased by turning the knob_____
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Counterclockwise
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Where do vaporizer standards dictate that you must be able to view the vaporizer fill level?
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On the front of the machine
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Can vaporizers be filled when in the on position?
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No (vaporizer standard)
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Can vaporizers tolerate maximum flows of both O2 and N20 with vaporizer on AND off?
When filled to capacity? |
Yes
Yes, (vaporizer standard) |
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TEC 6 vaporizer:
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For desflurane, heated to 39 degrees celsius, injection, no fresh gas flow passes through vapors
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Vapor pressure of desfluare at 39 degrees celsius?
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1500 mm Hg; heated vaporizer prevents vaporizer output decrease through heat lost from latent heat of vaporization
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Agent color codes:
Halothane Isoflurane Desflurane Sevflurane Enflurane |
Halothane: red
Isoflurane: purple Desflurane: blue Enflurane: orange Sevflurane: yellow |
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Interlock device
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Prevents more than one vaporizer from being turned on at the same time
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What is a possible source of leak within the vaporizer?
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Missing O-ring on the manifold gives a low pressure leak
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Potential error of wrong agent being placed in vaporizer?
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operator error- cannot rely on sense of smell to fill vaporizer, draining cannot be relied upon to completely empty vaporizer
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Tipping vaporizers:
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Can result in extra agent being available in the bypass outlet, and increased concentration will result
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Safety mechanism for filling vaporizers
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Keyed filling systems
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Overfilling a vaporizer could result in:
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Variable vaporizer concentration (could increase OR decrease); will increase if agent contaminates fresh gas flow line
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Do you fill vaporizers in the on or off position?
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Always when off; never turn on vaporizer during filling or overfilling could occur
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Most common place for leaks within vaporizer?
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Fill cap is loose; other sources include missing or damaged O-rings, interlock device, or loose fittings
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Desflurane vapor pressure at 20 degrees celsius:
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669 mm Hg
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Isoflurane vapor pressure at 20 degrees celsius
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240 mm Hg
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Sevoflurane vapor pressure at 20 degrees celsius
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170 mm Hg
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Halothane vapor pressure at 20 degrees celsius
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243 mm Hg
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Ethrane vapor pressure at 20 degrees celsius
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175 mm Hg
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Methoxyflurane vapor pressure at 20 degrees celsius
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22.5 mm Hg
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How do you calculate the % concentration:
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(partial pressure of agent/total pressure) x 100;
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Vaporizers are calibrated:
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To the specific vapor pressure of the agent it is designed for
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HLH
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If you add a high vapor pressure agent to a vaporizer that is designed to accept a lower vapor pressure agent, you will end up with too HIGH of a concentration of vapor (higher than dial setting) (overdose)
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LHL
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if you add a low vapor pressure agent to a vaporizer designed to accept a higher vapor pressure agent, your delivered concentration will be too LOW (lower than dial setting) (under dose)
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N20 can causes spontaneous abortion and birth defects in concentrations as low as ____ in animal studies?
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9 ppm
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What are some potential sources of leaks for N20?
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tank valves, high and low pressure machine connections, connections in the breathing circuit, defects in hoses, tubes, reservoir bags, or bellows, or at the Y connector
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What are some potential sources of exposure to N20 or other agents that CRNA can directly control?
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Leaving gas flow control valves and vaporizers on when not in use, spillage during filling, improperly fitting face masks, leaks around ETT cuff
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NIOSH recommendations for exposure to agents:
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20 ppm for N20 (aestiva says 25)
2 ppm of any halothanated agent or 0.5 ppm if N20 is also in use |
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Do NIOSH recommendations exist for exposure to the three most common anesthetic agents (sego, iso, and des)
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No
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5 basic components of a scavenging system:
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1. Gas collection assembly/breathing system reservoir- collects excess gases and delivers them to transfer tubing
2. Transfer tubing- conveys gases to interface 3. Interface: provides positive (and sometimes negative) pressure relief, and may serve as reservoir 4. Gas disposal assembly tubing: delivers gases from interface to disposal assembly 5. Gas disposal assembly: removes gases to a place that they can be safely released into the atmosphere |
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Size of transfer tubing for scavenger:
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19 or 30 mm, can be yellow color coded
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What are the ventilation standards for rooms with anesthetic gases according to the American Association of Architects?
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A minimum of 15 complete air changes per hour, with at least 3 changes of air with outside air
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excess patient gas is escapes through ___ when in bag mode, or through ____ when in vent mode?
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APL valve
Bellows spill valve Both go to intake ports of waste gas manifold |
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Waste gas scavenging systems can be ___ or ____
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Active or passive systems;
can also be open or closed systems |
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Active scavenging systems:
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Connect to the vacuum of the hospitals suction system, suction adjusted with needle valve
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Size of scavenger reservoir bag in active scavenger system
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3 L
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When the patient exhales, the scavenger reservoir will ____.
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Expand/inflate (deflates as gas is sucked out through vacuum during inspiratory phase)
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How should the needle valve on the scavenger be adjusted- how should the reservoir bag look?
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"One good turn;" should not be collapsed, but should remain less than half full
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If pressure in the scavenger reservoir builds up too high, gas...
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escapes into the room
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If the vacuum creates negative pressure on the patient circuit, the relief valve will ____
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lift up and allow room air into the assembly and protect the patient
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If using a passive scavenging system, make sure that___
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Needle valve is completely closed
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Passive scavenging systems connect ___
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the waste gas interface with the hospital ventilation system; may or may not have reservoir
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Common component of passive scavenging system
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Charcoal canister
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Rooms with passive scavenging systems should have
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High turnover HVAC systems with flow directed toward floor and vents
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Are open scavenging systems more or less safe for the patient? Why?
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Safer; there are no valves to potentially malfunction
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Are closed scavenging systems safer in terms of room pollution?
In both open and closed systems, what happens if the vacuum is not turned on? |
Not really
You are polluting the room with gases |
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Name three hazards associated with scavengers
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1. Barotrauma to patient if negative pressure relief valve fails (to remedy, turn off suction from scavenger, or disconnect scavenging connection from the back of the APL valve)
2. occupational exposure 3. Barotrauma or inability to ventilate |
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When would you want a short i time (i.e. a long e- time)
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When you want lots of time to exhale CO2 (asthmatics, COPD)
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What is a normal I-time in an adult?
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1.5- 2 seconds
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If you have a fixed i:e ratio, and you change the rate, what will happen to the i-time?
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It will also change automatically
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Prolonged inspiratory time may ___ venous return
Why? |
Decrease, due to prolonged inflation time
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Prolonged inspiratory time may increase _____, and cause ____.
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intrinsic PEEP (breath stacking), barotrauma
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8, 80, 800 rule
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Rate of 8, FiO2 80, and TV 800 will ventilate most adults
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What is the purpose of APRV mode?
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Used in critically ill patients to reduce barotrauma, prolonged inspiratory time with brief release for exhalation; decreases the difference between Phigh and Pmean
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What is the first and most important thing to do if you cannot figure out a ventilator problem?
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bag!
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More important than vent alarms, you should be looking at your patient for:
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color, chest rise, chest symmetry, how breath is being delivered (frequency, duration)
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Name 5 things that might cause a high airway pressure alarm
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1. Secretions/condensation in ETT
2. Patient biting 3.Patient fighting/coughing/trying to talk 4.Kink in tubing (vent or ETT) 5. Bronchospasm or pneumothorax (decreased compliance) |
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Name two things that might cause a low pressure alarm
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1. ETT not connected
2. ETT displaced (leak in circuit) |
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Name 4 things that may cause a high respiratory rate alarm:
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1. Patient discomfort/anxiety
2. Hypoxia 3. Hypercapnia 4.Secretions in ETT |
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Name 3 things that might give you a low exhaled volume alarm:
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1. Vent tubing not connected
2. occurrence of another alarm giving you reason that breath has not been fully delivered 3. Leak around ETT cuff |
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What factors could you manipulate to increase SpO2/PaO2?
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PEEP and FiO2
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What factors could you manipulate to alter pCO2?
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Rate, PC, TV, PS
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How does the concentration dial on a vaporizer work?
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It divides the flow of gas into two streams, one which travels through vapors, and one which bypasses it
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