Anesthesia machine - week 2 Flashcards
This week's lecture in class was focused on vaporizers. However, the study guide goes into other things as well.
Give five examples of how a vaporizer can become hazardous.
wrong agent used to fill vaporizer
tipping it over
overfilling
contaminants in the vaporizing chamber
leaks
How is agent delivery affected by changing altitudes?
decreased barometric pressure (high altitude) => increased delivery
increased barometric pressure (more than 1 atm) => decreased delivery
What does a flow-compensated vaporizer compensate for?
temperature
(To prevent fluctuations in vaporizer output owing to temperature changes, compensatory mechanisms are built in. Typically the use of a valve that changes flow through a vaporizer—commonly a bimetallic strip or an expansion element. As ambient temperature goes up, the bimetallic strip/expansion element diverts more gas flow through the bypass, because the gas flowing through the vaporizing chamber will pick up more agent (due to the higher vapor pressures at higher temperatures)
Which volatile agents are not delivered through variable bypass vaporizers?
Desflurane
(Desflurane’s high volatility and moderate potency preclude it’s use with contemporary variable-bypass vaporizers for two primary reasons: (1) at 20 degrees C, the vapor pressure of desflurane is near 1 ATMs (669 vs 760). (2) Traditional vaporizers lack an external heat source. Basically, the delivery of desflurane would be very unpredictable)
Where are variable bypass vaporizers located? Why?
Between the flowmeters and the common gas outlet.
To prevent administration of elevated levels of inhalation agent to the client by secondary back-flow.
How is a desflurane vaporizer (Tec - 6) different than other modern day vaporizers?
1) It has its own heater
2) No fresh gas flows through the desflourane sump. Instead, mixture occurs as gas is leaving the vaporizer
3) It cannot compensate for changes in altitude pressure
Why does Desflurane need a special vaporizer?
Highly volatile
1/5 as potent as other VAA’s
The vaporization required for desflurane produces a cooling effect that would overwhelm the ability of conventional vaporizers to maintain a constant pressure.
A tremendously high fresh gas flow is required to dilute the carrier gas to clinically relevant concentrations
It is possible to use Desflurane in a traditional flow over vaporizer?
Yes
(but you wouldn’t want to since the vaporizer for Desflurane is specifically designed to vaporize all of the VAA and make it more predictable and usable)
What would happen to desflurane if it were used in a flow over vaporizer at a high altitude, like on Mt. Kilimanjaro?
you would have a shit-ton being delivered
i attempted to reason this out, if it’s wrong go ahead and change it
What are the 6 components of the circle system?
Inspiratory and expiratory unidirectional valves
Inspiratory and expiratory corrugated tubes
Y-piece connector
Overflow or pop-off valve (APL)
Reservoir bag
Canister containing CO2 absorbent.
What are 5 advantages to using the circle system?
Constant inspired concentrations
Conservation of heat and humidity
Minimal OR pollution
Useful for closed-system, low-flow, and semi-open configurations
Low resistance (less than the endotracheal tube; not as low as in nonrebreathing circuits)
Which circle system component(s) generates the greatest resistance to breathing during spontaneous respiration?
1) valves in the inspiratory and expiratory limbs of the circuit
2) CO2 absorber
In a circle system, where is the dead space located?
the Y-piece
(Mechanical dead space in a circuit constitutes the area where inspiratory and expiratory streams share the same space. This dead space ends where the inspiratory and expiratory gas streams split apart. Because of the two unidirectional valves in the circle system, dead space is limited to just the Y-piece)
Why is re-breathing not a reasonable option with a semi-open system?
These systems do not utilize CO2 absorbent so if the fresh gas flow is set too low, the patient will rebreathe CO2 and potentially become hypercarbic/acidotic
What are the two main features (or lack of features) of a semi-open anesthetic breathing system?
1) Absence of valves to direct gases flowing to & from patient
2) Absence of carbon dioxide neutralization
(Because semi-open systems have no clear separation of inspired and expired gases, high FGF is required to prevent rebreathing)
What are some advantages of the semi-open breathing system?
lower cost
increased humidification
reduced heat loss
decreased release of anesthetic to the environment
Why is the adjustable pressure limiting valve important in the semi closed system?
Waste anesthetic gases are vented from the anesthesia system through the APL valve or through the ventilator’s relief valve
When does a closed anesthetic system exist?
Rarely
(The use of a closed circuit represents an extreme of anesthetic administration, one infrequently employed because few systems completely eliminate leakage of gas from the circuit.
Anesthetists often apply a deliberate leak of approximately 200 mL/min by sampling gases for oxygen, carbon dioxide, and anesthetic analyses.)
Name four main advantages to using a closed breathing system.
cost reduction
increase in tracheal warmth & humidity
decrease in potential exposure of OR personnel to trace or waste gas
What are two advantages of the open anesthetic breathing system?
light weight
easily sterilized
What are two disadvantages of the open anesthetic breathing system?
unrecognized disconnection
kinking of fresh gas hose
When using a T-piece, what flow rate must be used to avoid rebreathing?
A T-piece must have total flow greater than inspiratory flow in order to avoid rebreathing.
(exactly what that flow is, I don’t know)
The Mapleson D system when modified is also known as what type of circuit?
Bain circuit
What is the most commonly used system for delivering anesthetic gases and O2 to children and adults?
Circle system; gives most control over all variables
What is the problem with placing the O2 sensor at the common gas outlet?
the common gas outlet has a mixture of volatile agent and gases
Describe four actions you can take to test the low pressure system.
Check initial status of low pressure system
- Close flow control valves and turn vaporizer off - Check fill level and tighten vaporizer filler caps
Perform leak check of machine low pressure system
- Verify that the machine master switch and flow control valves are OFF - Attach “suction bulb” to common gas outlet - Squeeze bulb repeatedly until fully collapsed - Verify bulbs stays fully collapse for at least 10 seconds - Open one vaporizer at a time and repeat collapsing and evaluation of the bulb - Remove suction bulb and reconnect fresh gas hose
Turn on machine master switch
Test Flowmeters
- Adjust the flow of all gases through their full range and check for smooth operation of floats and undamaged flow tubes - Attempt to create a hypoxic O2/N2O mixture and verify correct changes in flow and/or alarm
What is the most abundant constituent in soda-lyme and baralyme?
CaOH2 (Calcium hydroxide)
What is the name for the type of chemical reaction occurring in the carbon dioxide absorber?
Neutralization of Carbon Dioxide
or
Heat of Neutralization
Why does the volume returned on an ascending bellows not reflect true tidal volume?
Ventilators impose a slight resistance at the end of exhalation, at which time the pressure in the bellows rises enough (2 to 4 cm H2O) to open the spill valve.
(during exhalation, the bellows expands upward)
What is present inside and outside the bellows (gases/agents…)
outside - the driving gas (usually oxygen, but can be air, or a combo of both)
inside - everything the patient exhales (ie VAA, O2, N2O, CO2, etc)
How does positive pressure ventilation affect pulmonary circulation? Cardiac Output?
Heart Rate? Blood pressure? Venous return?
Cardiac output is decreased due to a decreased venous return which can lead to a decrease in systemic blood pressure.
If heart rate is increased (as is should with a decrease in stretch of the baroreceptors) blood pressure may remain normal.
The application of heat will increase or decrease saturated vapor pressure?
increase
because more molecules will enter the gas phase
The application of cold will increase or decrease saturated vapor pressure?
decrease
fewer molecules enter the gas phase
VAAs with a high vapor pressure that are placed in a vaporizer that is meant for a VAA with a low vapor pressure will produce what kind of output?
high output
high - low - high
VAAs with a low vapor pressure that are placed in a vaporizer that is meant for a VAA with a high vapor pressure will produce what kind of output?
low output
low - high - low
