Vaporizers Flashcards
What is the purpose of a vaporizer
Add anesthetic gas (vapor) into the path of fresh gas flow that is directed to the common gas outlet
What is a vaporizer composed of?
molecules (in the gaseous phase) of a substance that is a liquid at room temperature & 1 atm of pressure
What are volatile liquids?
- Volatile liquids: all liquids that have a high vapor pressure at room temperature
- Volatile liquids evaporate readily at normal temperature
What is the calibration of vaporizers?
at 1 atm (760 mmHg)/20 degrees C
What is the overall concept of the vaporizer?
The AGM vaporizer is where liquid anesthetic is evaporated - fresh gas flow from flowmeters enter vaporizer where volatile anesthetic liquid is present and flows over the liquid resulting in evaporation from the surface of the volatile anesthetic liquid within the vaporizer
What happens to the volatile liquid anesthetic?
Molecules on the surface of the volatile liquid anesthetic (iso, sevo, des) evaporate (escape into the gas phase): producing anesthetic vapor
What does rate of vaporization depend on?
- Temperature
- Vapor pressure of the liquid
- Partial pressure of the vapor above the evaporating fluid
What effect does increased temperature have on rate of evaporation?
Increased temp increases rate of evaporation of a liquid and vice versa
How does the evaporation process effect the anesthetic liquid?
Evaporation process causes cooling of anesthetic liquid due to heat energy being used as the molecules convert from liquid to vapor state
What is the relationship of the evaporation process effect the anesthetic liquid? What prevents this?
Cooling slows vaporization = reduced volatile anesthetic delivery
- To prevent this in AGM vaporizers: Use of substances such as copper that have high thermal conductivity and high thermal capacity
What are the vaporizer classifications?
- Variable bypass
- Measured flow
- Tec 6 Injector
What are examples of variable bypass vaporizers? (4)
- Tec 4, 5, 7
- Aladin (Aisys, Avance)
What are the two FGF streams for a variable bypass vaporizer?
Two FGF streams: vaporizing stream & bypass stream
What is the control dial of variable bypass vaporizer?
Control dial: controls what portion of fresh gas flow to come into contact with the volatile anesthetic liquid and pick up anesthetic vapor
What is the splitting ratio?
Amount of gas entering the vaporizing chamber divided by total fresh gas flow
What does setting the control dial of the variable bypass vaporizer determine?
Setting the control dial to the desired concentration determines the resistance to flow in the internal channels
What does a higher precentrage of the variable bypass vaporizer allows for?
- Administering a higher percentage allows more fresh gas flow through the vaporizing chamber
- The gas that flows through the vaporizing chamber known as carrier gas or chamber flow
- Fresh gas flows over the liquid within vaporizing chamber to pick up anesthetic vapor known as carrier gas or chamber flow
How is the carrier gas fully saturated?
To ensure the carrier gas is fully saturated it flows thru wicks and baffles (imagine a maze)
What is a fully saturated carrier gas combined with?
Fully saturated carrier gas is then combined with remaining fresh gas flow that was diverted away from the vaporizer chamber (also known as the bypass flow)
Why are temperature safety devices built in to the variable bypass vaporizer?
Temperature compensation devices are built in to ensure more gas is directed into vaporizing chamber if the vaporizer cools
What is true about specific agents in the variable bypass vaporizer?
Agent specific and inhalational agents must be used in the specific, agent-calibrated vaporizer
Where is the Variable Bypass Vaporizer positioned?
Positioned outside of the breathing circuit
What is the Variable Bypass Vaporizer classified as?
Often classified as variable bypass, flow-over, temperature compensated, agent- specific, out-of-circuit vaporizers
What does A refer to?
The liquid and vapor are in equilibrium
What does B refer to?
The application of heat causes the equilibrium to shift so that more molecules enter the vapor phase, as illustrated by the increased density of dots above the liquid
What does the letter C represent?
Lowering the temperature causes a shift toward the liquid phase and a decrease in vapor pressure
What does the letter D?
Passing a carrier gas over the liquid shifts the equilibrium toward the vapor phase. The heat of vaporization is supplied from the remaining liquid. This causes a drop in temperature
How does Variable Bypass Vaporizer Temperature Compensate?
Bimetalic Strip
Review the components of the Variable Bypass Vaporizer.
- Splitting ratio = Variable bypass
- Vaporizing stream vs Bypass stream
- Flow over vaporization
- Baffles and wicks to increase contact
- Automatic temperature compensation mechanism
- Calibrated and agent specific
- Positioned out of circuit
When is the Measured-Flow (Vernitrol) vaporizer used?
Used in the military or missionary work
What does the operator calculate Measured-Flow (Vernitrol) vaporizer?
Operator calculates how much gas to bubble through anesthetic liquid
What happens if a Measured-Flow (Vernitrol) vaporizer cools?
- If vaporizer cools operator recalculates and sets a new chamber gas flow
- Manual temperature compensation
Measured-Flow (Vernitrol) vaporizer is _________ circuit
Out of breathing circuit
What is the property of the Tec 6 Injector Vaporizer?
- Heated, dual circuit vaporizer
- Fresh gas flow passes through the vaporizer in one circuit
What is true about the fresh gas flow and Tec 6 Injector Vaporizer?
Fresh gas flow never contacts the liquid agent, rather the appropriate amount of vapor is added to the fresh gas as it flows through the vaporizer
What are the two points of control for the Tec 6 Injector Vaporizer?
- Setting on concentration control dial
- Transducer that responds to the amount of fresh gas flow
Define transducer that responds to the amount of fresh gas flow.
Increased fresh gas flows = increasing amounts of vapor added to circuit
Define setting on concentration control dial.
Increasing concentration = increasing amounts of vapor added to circuit
What is the temperature components of the Tec 6 Injector Vaporizer?
- To maintain a known vapor pressure the Tec 6 is heated to 39◦C
What is the vapor pressure produced by the Tec 6 Injector Vaporizer?
Produces a vapor pressure of ~1500mmHg
Review Tec 6 Injector Vaporizer schematic.
What voalite anesthetics use Tec 6 Injector Vaporizer?
Des
What is the interlocking system of the vaporizers?
- Prevents turning on more than agent simultaneously
- Locks vaporizers in place to decrease leaks
What does the interlocking system of the vaporizer ensure?
- Ensures only gas from the vaporizer that is on is entering the system
- Ensures trace vapor output is minimal when vaporizer is off
How do you fill vaporizers?
- Funnel type
- Key filled (preferred)
Liquid fill levels indicators must be _____ to operator
Visible
When can filling of the vaporizer occur?
- Filling occurs with vaporizer in off position
- Tec 6 can be filled while in use
Review Aladin Vaporizer Cassette Management schematic.
What does Aladin Vaporizer Cassettes use?
Use one central electronic control mechanism for all agents
When is the Aladin Vaporizer Cassettes checked?
- Cassette is check as part of the daily electronic checklist
What is the Aladin Vaporizer Cassettes not sensitive to?
Not sensitive to tipping like other vaporizers
What is the variable bypass checklist?
- Turned off
- Filled
- Tightly closed filling cap
- Interlocking system is functional
- Older machines may need to be checked for leaks as well
What is the Tec 6 pre-operative checklist?
- Check alarm battery and replace if necessary
- Turn on to 1%, d/c plug and assess alarm function w/in 15 seconds
- Use mute button to test all alarms and the display
What is important to remember about volatile inhaled anesthetics?
Incorrect or unintended agent administration (each agent is color-coded; a liquid volatile agent is a drug, still must read the label on the volatile liquid bottle & confirm correct agent/correct vaporizer before filling the vaporizer)
What are some hazards of vaporizers?
- Tipping
- Overfilling
- Lack of preventative maintenance
- Leaks
- Electronic failure
How far can vaporizers be tipped?
Do not tip past 45 degrees
Lack of preventative maintenance= ____________
Loss of calibration
What happens if a vaporizer specific for an agent with a low vapor pressure (e.g. enflurane or sevoflurane) is misfilled with an agent with a high vapor pressure (e.g. halothane or isoflurane)?
the output concentration of the agent will be greater than indicated on the concentration dial.
What happens if a vaporizer specific for an agent with a high vapor pressure (e.g. halothane or isoflurane) is misfilled with an agent with a low vapor pressure (e.g. ethrane or sevoflurane)?
the output concentration of the agent will be less than indicated on the concentration dial.
How much liquid agent does a vaporizer use per hour?
3 x fresh gas flow (FGF) in L/min x vol % = mL liquid used per hour
If you are running 2L/min oxygen and 2L/min nitrous oxide and Forane at 2% concentration, how much liquid agent is being used per hour?
3 x 4 x 2 = 24mL/hour
Identify the common gas outlet.
What is the purpose of breathing circuits?
Delivery of oxygen and anesthetic agent to the patient and elimination of carbon dioxide from the patient
How is carbon dioxide removed from breathing circuits?
Carbon dioxide removed by fresh gas flows or absorption in carbon dioxide absorbent granules
What effects resistance in the circuit?
- Length and diameter of the circuit
- Fluidity (avoiding bends in the circuit and valves)
- Maintaining laminar flow
What are the effects of rebreathing in the anesthesia circuits (unlike ICU vent circuits)?
- Decreases costs
- Increased tracheal warmth and humidity
- Decreases OR exposure to trace and waste gases
When does rebreathing increase?
- Rebreathing increases as fresh gas flow decreases and vice versa
- When should you have increased flows, and when should you decrease them?
What is dead space?
- Increased mechanical dead space from a circuit allows for rebreathing of carbon dioxide
What is the rationale for why ventilator TV set greater than the volume of a spontaneous breath?
Dead space
Where does dead space end?
Dead space ends where the inspiratory and expiratory gas streams diverge
Where does dead space end in the circle system?
at the Y piece of circuit
What effects dead space?
- It is not increased by longer inspiratory & expiratory corrugated plastic hoses
- Use of a face mask is associated with more dead space than an ETT
What are the classifications of breathing circuit?
- Open
- Semi-open
- Semi-Closed
- Closed
What is the components of the open breathing circuit (Reservoir, Rebreathing and Examples)?
Reservoir: No
Rebreathing: No
Examples:
- Open drop
- Insufflation
- Nasal cannula
- Simple face mask
What is the components of the semi-open breathing circuit (Reservoir, Rebreathing and Examples)?
Reservoir: Yes
Rebreathing: No
Examples:
- Circle at high fresh gas flows (greater than minute ventilation)
- Nonrebreathing circuit
What is the components of the semi-closed breathing circuit (Reservoir, Rebreathing and Examples)?
Reservoir: Yes
Rebreathing: Yes (Partial)
Examples: Circle at low fresh gas flows (less than minute ventilation)
What is the components of the closed breathing circuit (Reservoir, Rebreathing and Examples)?
Reservoir: Yes
Rebreathing: Yes (Complete)
Examples: Circle at extremely low fresh gas flow, with adjustable pressure-limiting valve closed
Define open breathing system.
Anesthetic gases and oxygen are blown directly across the face
What is not present on open systems?
- No valves, reservoir or carbon dioxide absorber
- No dead space
What is higher risk with open systems?
Increased risk for airway fire
What are examples of open systems?
- Blow by oxygen
- Mask held over the patients face without touching the face
What is an example of a non rebreathing circuit?
Mapleson D & Bain
What is the components of Mapleson D nonrebreathing circuit?
During the pause between expiration and the next inspiration fresh gas fills the corrugated limb forcing the previously exhaled gas toward the reservoir
What is true about the Mapleson D?
If fresh gas flow is sufficient no rebreathing occurs
What is sufficent gas flow for the mapleson D non rebreathing circuit?
Sufficient is 2-3 times minute ventilation (or 5L/min)
Who benefits from a mapelson D non rebreathing circuit?
Very low resistance to breathing so are good for all ages
What are the freatures of a Mapleson D non-rebreathing circuit?
- No unidirectional valves
- No soda lime for carbon dioxide absorption
- Fresh gas flow determines amount of rebreathing
- Resistance and work of breathing are low
What is the Bain non-rebreathing circuit?
Similar to Mapleson D but fresh gas hose directed coaxially within the corrugated limb giving inhaled gases greater heat and humidity
How can repiratory acidosis occur with Bain non-rebreathing circuit?
Kinks in fresh gas hose turn corrugated hose into dead space that can result in respiratory acidosis
What test needs to be done with the Bain non rebreathing circuit?
Use Pethick’s test or similar to test circuit
What is the components of Pethick’s test or similar to test circuit?
- Occlude patient end of the circuit at the elbow
- Close the APL valve
- Fill the circuit with the oxygen flush valve
- Release the occlusion at the elbow and flush
- A venturi effect will flatten the reservoir bag if the inner tube is patent
Identify the damaged versus the intact tube according to the Pethick’s Test.
What is the circle system?
Assembly of components which connects the patient’s airway to the anesthesia machine
What does the circle system create?
Creates an artificial atmosphere into which the patient breathes
Review the Circle system schematic.
What is the most popular breathing system in the US?
Circle system
What is the purpose of the circle system (5)?
- Cleanses carbon dioxide chemically
- Allows rebreathing of all other exhaled gases
- Allows gas flow in a circular pathway through separate inspiratory and expiratory channels
- The direction of flow is determined by two unidirectional valves
- Ensures all exhaled gas is directed through absorbent granules and cleaned of carbon dioxide
What are the components to the circle system?
- Fresh gas inflow source
- Unidirectional valves
- Corrugated tubing
- Y connector
- Overflow
- APL/Pop off valve
- Reservoir bag
- Carbon dioxide canister & absorbent granules
What is the Circle System Variation - Coaxial?
Inspiratory limb is contained within the expiratory limb
What are the three valves that ensure unidirectional flow in the circle system?
- Pop off valve
- Inspiratory valve
- Expiratory valve
What is another name for the Adjustable Pressure Limiting Valve?
APL or pop off valve
What is the APL or pop off valve release?
A user adjustable valve that releases gases to the scavenging system
What does the APL valve provide?
Intended to provide control of the pressure in the breathing system
What are the types of circle systems? (3)
- Closed
- Semi Closed
- Semi Open
What is the principle components of the closed circle systems?
- Fresh gas inflow exactly equal to patient uptake
- Complete rebreathing after carbon dioxide absorbed and pop off valve closed
What does the Fresh gas flow of the closed circle system?
FGF 300-500mLs
What is the principle components of the semi closed circle systems?
- Some rebreathing occurs
- FGF and pop off valve at intermediate values
What is the fresh gas flows of the semi closed circle system?
FGF 3-6L
What is the components of the semi open circle system?
- No rebreathing
- High FGF
What is the fresh gas flow of the semi open circle system?
FGF = 1 to 1.5 times minute ventilation
What are advantages to the circle system?
- Constant inspired concentrations
- Conservation of respiratory tract heat and humidity
- Minimal OR and environmental pollution
- Useful for closed system, low flow and semi open configurations
- Low resistance
What is the disadvantage of the circle system?
- Relatively complex
- Opportunities for misconnection or disconnection
- Malfunctioning unidirectional valves cause serious problems, e.g. rebreathing or occlusion
- Less portable than nonrebreathing circuits
- Increased dead space
