Anesthesia Machine Flashcards
Where does the high pressure system begin and end?
begins at the cylinder and ends at the cylinder regulators
Where does the intermediate pressure system begin and end?
begins at the pipeline and ends at the flowmeter valves.
Where does the low pressure system begin and end?
begins at the flowmeter tubes and ends at the common gas outlet
When you connect a bulb to the common gas outlet and create negative pressure what type of leak test are you performing?
Low pressure leak test (negative pressure test)
The low pressure leak test is testing from what point in the anesthesia machine to what other point?
from the flowmeter valves to the common gas outlet
(this includes the entire low pressure system and the flowmeter valves which are the end of the intermediate pressure system)
How do you perform a high pressure leak test?
closing the APL valve, pressurizing the circuit, and observing the airway pressure gauge (pressure should remain constant)
During a high pressure leak test if the machine does NOT have a check valve what parts of the machine are being assessed (tested)?
the breathing circuit and the entire low pressure system
During a high pressure leak test if the machine does have a check valve what parts of the machine are being assessed (tested)?
the breathing circuit and the low pressure system up to the check valve (which would only be the common gas outlet part of the low pressure system)
(it does NOT assess for a leak between the check valve and the rest of the low pressure system which would be the the vaporizers and flowmeter tubes)
What are the 4 possible components of the low pressure system?
flowmeter tubes
vaporizers
check valve (if present)
common gas outlet
During the high pressure test if the machine has a check valve then what parts are not being tested that are being tested if the check valve is not present?
with a check valve in place the high pressure test DOES NOT assess the vaporizers and flowmeter tubes because these are upstream from the check valve if it is present.
What does SPDD model stand for?
Supply
Processing
Delivery
Disposal
in the SPDD model the breathing circuit would be which part?
Delivery
in the SPDD model the pipeline to the back of the anesthesia machine or cylinders would be which part?
Supply
in the SPDD model the inside the machine up to the common gas outlet (vaporizers) would be which part?
Processing
in the SPDD model the scavenging system would be which part?
Disposal
Name the five tasks of oxygen?
- 02 pressure failure alarm
- 02 pressure failure device (failsafe)
- 02 flowmeter
- 02 flush valve
- Ventilator drive gas
What type of ventilator does not require a drive gas?
Piston driven
Which safety system is in place to prevent inadvertent misconnections of the gas cylinders?
PISS
Which safety system is in place to prevent inadvertent misconnections of the gas hoses?
DISS
What is the 02 pressure in the cylinder vs upon entry into the intermediate system?
02 cylinder pressure = 1900 psi
02 pressure in the intermediate system = 50 psi
What is one thing that can bypass the PISS system (that you should never do)
two washers between the hanger yoke assembly (there should only be one washer)
PISS configuration for air, oxygen, and Nitrous
air = 1,5 oxygen = 2,5 nitrous = 3,5
What is pipeline pressure vs intermediate system pressure?
They are about the same 45-50psi for the gas hoses and 50 psi in the intermediate system
When are the only times that cylinders should be turned on?
when checking them during the machine check or in the event of pipeline failure. (They should never be left in the on position when not in use)
What is the only way of determining a cylinders contents?
looking at the LABEL not the color
Standard US colors for air, oxygen, and nitrous?
air = yellow oxygen = green Nitrous = blue
WHO colors for air, oxygen and nitrous?
air = white and black oxygen = white Nitrous = blue
Air:
max pressure
max volume
pin configuration
max pressure= 1900 psi
max volume = 625 L
pin configuration = 1,3
Oxygen:
max pressure
max volume
pin configuration
max pressure= 1900 psi
max volume = 660 L
pin configuration = 2,5
Nitrous: max pressure max volume pin configuration Full weight Empty weight
max pressure = 1900 psi max volume = 660 L pin configuration = 3,5 full weight = 20.7 lb empty weight = 14.1 lb
Formula for minutes left before tank expires for oxygen or air?
- Tank capacity / full tank pressure = contents remaining / gauge pressure \
- contents remaining / flow rate = minutes left before tank expires
Oxygen exists as a gas inside the cylinder why and what is its critical temp?
oxygen exists as a gas inside the cylinder because it’s critical temperature is BELOW room temp. at -119 C
Does nitrous exist inside the cylinder as a gas or liquid and why?
N2O exists as a liquid (and a tiny bit as a gas) inside the cylinder because it’s critical temperature is ABOVE room temp at 36.5 C
When will the pressure gauge on nitrous start to decrease? How much nitrous is left?
The bourdon pressure gauge on nitrous will only decrease below 745 psi when ALL of the liquid nitrous is gone and only the gas remains.
This means the the cylinder is 3/4 EMPTY so approximately 400 L of Nitrous remains in the tank, thus change the cylinder anytime the psi falls below 745 psi
What is the most delicate part of the cylinder?
Cylinder valve
If you have an empty cylinder on the machine and you do not have a cylinder to replace what should you do?
insert the hanger yoke plug because if no cylinder is present and no yoke plug is present then in the event of the check valve failing- gas that should be going to the patient will exit the machine
What is the fire triad?
oxidizer
fuel
igniter
In the fire triad what are oxygen and nitrous?
oxidizers
What are the three examples of safety relief devices on cylinders?
fusible plug that melts at elevated temperatures
valve that opens at elevated pressures
frangible disk that ruptures under pressure
What is a fusible plug made of?
Wood’s metal : bismuth, lead, tin, and cadmium
BLT with Cheese
If the yoke retaining screw punctures the safety relief valve what may happen?
cause the cylinder to leak
What issue does oiling the cylinder valve cause?
increases the risk of fire because now you have fuel (oil) and an oxidizer (nitrous or oxygen) and now you only need a heat source to start a fire
How should you open a cylinder when checking it or putting it to use?
Slowly open the cylinder this is known as “CRACKING” and this allows for the flush valve outlet to clean of dust and debris
ASTM, who are they and what is their job?
American Society for Testing Materials (ASTM) sets standards for required components of the anesthesia machine
The standard document is called the STM F1850
DOT, who are they and what is their job?
United States Department of Transportation, sets the standards for compressed gas cylinders.
FDA, who are they and what is their job?
Food and Drug Administration, created in 1993 FDA Anesthesia Machine Pre-use checkout procedures
OSHA, who are they and what is their job?
Occupational Safety and Health Administration, sets the standards for acceptable occupational exposure to volatile anesthetics
How often must a cylinder be tested?
every five years unless it has a special permit which is denoted by a five pointed star and then it is good for ten years. The date of the last test must be clearly noted on the cylinder.
What pressure is a cylinder tested at?
1.66 x it’s service pressure (max psi it can hold)
The US DOT requires some information be on the cylinder label, this would include what kind of things?
Government agency (DOT) type of metal used to construct the cylinder maximum filling pressure serial number manufacturer owner date of last inspection
(it does not state that the gas type has to be listed… idk since you are supposed to check the label to know the gas, maybe that is not required by DOT)
If a leak develops distal to the flowmeters will the oxygen pressure failure device activate?
NO, the leak must be in the intermediate pressure system not the low pressure system
What is the main purpose of the oxygen pressure failure device?
What three specific instances will it alert you about?
monitor for and protect against low oxygen pressure in the anesthesia machine.
- depleted oxygen tank
- drop in pipeline pressure
- disconnected oxygen hose
Does the failsafe device monitor oxygen concentration or oxygen pressure?
The failsafe device (oxygen pressure failure device) monitors the pressure in the oxygen line not the concentration because it is the pressure that keeps the fail-safe valve open.
(thus if their is a pipeline crossover the failsafe device would still work and not alert you if the pressure is maintained in the oxygen line, it does not have to be oxygen)
Which system does the failsafe device reside in?
intermediate pressure system
The failsafe device has a threshold alarm that will sound when what occurs?
when the oxygen pipeline pressure falls below 28-30 psi
it is the oxygen line, it may not be oxygen in the case of a pipeline crossover
In the failsafe device their is a pneumatic device that reduces or stops the flow of nitrous when oxygen pipeline pressure falls below?
20 psi
what is the only gas that passes directly from its source to its flow valve at the flowmeter?
oxygen
(air and nitrous must first pass through a failsafe device, BUT some newer machines are letting air pass directly like oxygen so the patient can be ventilated with air if oxygen supply is not available)
There are two types of oxygen pressure failure devices, one by Ohmeda and one by Drager, what is the difference?
Ohmeda = if oxygen pressure falls below 20 psi the nitrous shuts off (all or nothing)
Drager = as pipeline oxygen pressure decreases their is proportionate reduction in nitrous.
(some newer machines by Ohmeda allow for variable flow)
The hypoxia prevention safety device on the anesthesia machine will?
limit the nitrous oxide flow to three times oxygen flow
What does the Hypoxia prevention safety device do?
it is a proportioning device that does not allow you to set a hypoxic mixture at the flow control valves.
What is the max amount of nitrous you can adminster with the anesthesia machine?
75% is N2O max
In the Ohmeda machine is the nitrous oxide flowmeter and the oxygen flowmeter mechanically or pneumatically connected?
Ohmeda has a mechanical and pneumatic component.
The oxygen and Nitrous flowmeter are mechanically linked by a chain, it also incorporates a second stage regulator for Oxygen and nitrous which is the pneumatic component.
If you adjust the flow control valves in such a way that would create a hypoxic mixture, a gear engages and oxygen flow is automatically increased.
Does the Drager machine have a mechanical or pneumatically controlled hypoxia prevention device?
oxygen and nitrous flow is connected pneumatically.
If you adjust the flow control valve in such a way that would create a hypoxic mixture the supply pressure of nitrous oxide going to the flowmeter will be reduced to maintain the 3:1 ratio
What does pneumatic mean?
operating by air or gas under pressure
What is the Ohmeda proportioning device called and what is the Drager device called?
Ohmeda = link 25 system
Drager = oxygen ratio monitor controller
Four situations in which the proportioning device on the anesthesia machine can not prevent a hypoxic mixture?
oxygen pipeline crossover
leaks distal to the flowmeter valves
administration of a third gas (helium)
defective mechanic or pneumatic components
What is the beginning of the low pressure system?
Thorpe tubes (flowmeter)
What controls and measures the fresh gas flow that travels towards the vaporizers and common gas outlet?
The flowmeter (Thorpe tubes)
Which types of floats are read from the top?
all but the ball which would include: skirted, plumb bob, and nonrotating
Which type of float is read from the middle?
ball
What is the annular space in a flowmeter tube?
area between float and side wall of the flowmeter
When talking about flowmeters and their design what does “variable orifice” provide?
a constant gas pressure throughout a wide range of flow rates
narrowest at base and widens along its ascent would describe what in relation to flowmeter design?
internal diameter
The position of the indicator float is determined by two opposing forces, which are?
the fresh gas flow pushes the indicator float up
gravity pulls the indicator float down
If any component of the flowmeter is damaged what must occur?
The entire unit must be replaced
Why is a leak in the flowmeters problematic?
the flowmeters are distal to all the safety devices in the anesthesia machine other than the oxygen analyzer, thus their is only one component that can catch the problem.
The order of the flowmeters is important, where should the oxygen flowmeter be positioned and why?
closest to the manifold which is the farthest to the right in the US
By the oxygen being closest to the manifold it will not flow backwards or into another gas if a leak occurs in any other flowmeter, BUT if a leak occurs in the oxygen tube then all bets are off. By it being farthest to the right in the united states it limits the number of possible hypoxic mixtures to only an oxygen tube leak.
If the Re is less than 2,000 then the flow will be?
This makes the flow dependent on?
Who’s equation is this?
Laminar flow
dependent on gas viscosity
Poiseuille equation
If the Re number is greater than 4,000 then the flow will be?
This makes the flow dependent on?
Who’s law?
Turbulent flow
dependent on gas density
Graham’s law
What is the Reynold’s number equation?
Re = density x diameter x velocity / viscosity
What are the steps for calculating Fresh Gas Coupling?
- convert fresh gas flow from L/min to mL/min
- convert the I:E ratio to time and use the inspiratory portion in your calculation
(step one x step two) - Divide the tidal volume you’ve calculated from step one to step two and divide it by the RR
- Add the volume set on the ventilator to the FGF during inspiration (tidal volume on the machine + step 3 = tidal volume)
The entire calculation looks like this:
4,000mL/min x (1/3) / 10 breaths/min = 133mL
133mL +500 mL = 633 mL tidal volume
(circuit compliance is not part of this equation)
If a machine decouples FGF from tidal volume what does that mean?
That FGF is not an additional volume added into the set tidal volume like it is with machines that do NOT decouple, that what you set on the machine is actually what the patient gets.
How do you calculate compliance?
take the circuit compliance and multiply it by the peak pressure and then subtract that number from the tidal volume
(circuit compliance mL/cm H2O x peak pressure cm H2O - tidal volume)
What is the simple formula for compliance?
compliance = change in volume / change in pressure
How do you determine the splitting ratio?
setting the concentration on the dial
The gas that enters the vaporizing chamber and picks up volatile anesthetic becomes what percentage saturated?
100%
What flow rates through the vaporizer can lead to reduced vaporizer output?
flow less than 200ml/min (2L/min) greater than 15 L/min
If a vaporizer is tipped over what should you do?
you should run a high FGF through the vaporizer for 20-30 min because a concentrated amount of anesthetic may be exiting.
Is the vaporizer positioned out of circuit or in circuit?
out-of-circuit
What is the pumping effect?
Anything that causes gas that has already left the vaporizer to re-enter the vaporizing unit can cause the pumping effect.
most common cause of a vaporizer leak?
loose filler cap
Most common location of a leak to occur in the low pressure system?
internal leak in the vaporizer
Formula to predict how long your agent will last?
vol% x FGF (L/min) x 3 = mL of liquid anesthetic used per hour
If the tec 6 vaporizer does not work by variable bypass then how does it work?
The Tec 6 injects a precise amount of vaporized desflurane directly into the fresh gas flow.
Is desflurane less or more potent than the other volatile gases?
less potent that is why it takes 6.6 for a MAC
Which volatile gas has a vapor pressure close to atmospheric pressure?
Desflurane
Desflurane must be used in the Tec 6 vaporizer, what does the vaporizer do to the gas?
heats and pressurizes desflurane, heats it to 39 degrees C and pressurizes it to two atm.
At what temp. does desflurane boil?
just above room temp. at 22 C
Desflurane’s vapor pressure is how many times higher than those of the other agents?
3-4 times higher
What determines the depth of anesthesia for a patient?
partial pressure of VA in the brain (not the concentration)
Will a lower ambient pressure require a higher or lower dial setting for desflurane?
lower ambient pressure = elevation thus a higher setting is needed
will a higher ambient pressure require a lower or higher setting for desflurane?
The higher ambient pressure (hyperbaric) will require a lower setting on the desflurane dial
What are the two types of oxygen analyzers?
galvanic fuel cell
paramagnetic device
What are the details (calibration and consumption) about a galvanic fuel cell?
Must be calibrated daily.
The components are consumable, so they must be replaced over time.
What are the details (calibration and consumption) about a paramagnetic device?
self-calibrating
there are no consumable components
compared to the galvanic it has a faster response time
What is the most common site of a leak in the breathing circuit?
circuit disconnect at the Y piece
2nd most common site is the C02 cannister
Does the oxygen analyzer monitor 02 concentration or pressure?
concentration
What device will detect an oxygen pipeline crossover?
oxygen analyzer (NOT the pressure failure device or proportioning system)
What is the oxygen consumption for a normal adult?
250mL//min
What are some possible causes of reduced Fi02 during low flow anesthesia?
sepsis, pain, sympathetic stimulation, thyrotoxicosis, fever
During closed circuit anesthesia the provider tries to match oxygen delivery to the patients consumption of oxygen, if consumption increases but delivery remains the same you can create a hypoxic mixture… what will detect this?
oxygen analyzer
In the event of oxygen pipeline crossover what are the first two steps you MUST do?
Turn ON the oxygen cylinder and DISCONNECT the pipeline oxygen supply.
if there is adequate oxygen pipeline pressure just turning on the tank will not use oxygen tank gas, you must disconnect the hose.
When the oxygen analyzer alarms, it is best to assume what?
pipeline crossover has occurred until other causes can be ruled out
After you have turned on the oxygen tank and disconnected the pipeline oxygen what should you watch for next?
Verify that the oxygen concentration in the breathing circuit is increasing.
If not, you should assume a machine malfunction and you should ventilate the patient with an Ambu, be sure to use a different oxygen tank or room air.
If you are trying to conserve tank oxygen because you have disconnected pipeline oxygen, what can you do to conserve tank oxygen?
Conserve tank oxygen by using low flows.
If your machine uses oxygen to drive the bellows you will want to hand ventilate the patient to conserve oxygen.
If air is used to drive the bellows or it is a piston machine then the patient can remain on the vent.
What is being described:
Provides a path for oxygen to travel from the intermediate pressure system to the breathing circuit, it bypasses the low pressure system?
oxygen flush valve
What is the oxygen flow that pressing the oxygen flush valve exposes the patient to? (2)
35-75 L/min (not PSI)
Oxygen pressure of approx. 50 psi (pipeline pressure)
Is the ventilator spill valve open or closed during inspiration?
CLOSED
When the patient is on the ventilator and you need to press the oxygen flush valve, should you do so during inspiration or expiration?
expiration
Tell me how the drive gas, bellows, spill valve all work during inspiration on the vent?
During inspiration the drive gas pushes down on the bellows to compress them and force air into the patients lungs, the spill valve is not open because we want the compressed gas to go into the patient and not the scavenger system.
It is the drive gas that closes the spill valve and the fresh gas from the ventilator goes into the patient.
Tell me how the drive gas, bellows, and spill valve work during exhalation?
Expired gas refills the bellows and the bellows fill completely. When circuit pressure is greater than 2-4 cm H20 the spill valve opens and expired gas is directed through the spill valve into the scavenger system.
The flow of the drive gas is stopped during exhalation.
Which is better for the patient fresh gas decoupling or fresh gas coupling?
Fresh gas decoupling sounds better because the actual tidal volume you set on the vent is what is delivered to the patient. There is less risk for barotrauma because the set tidal volume is not combined with FGF and even the oxygen flush valve.
What is the inspiratory pressure limiter?
limits the breathing circuit pressure during inspiration. When the breathing circuit pressure rises above a set point the excess gas is vented out the scavenger.
If your oxygen flush valve becomes stuck what will result?
barotrauma
Bellows are classified by their movement during inspiration or expiration?
movement during expiration
If you have bellows on your machine would you assume that the fresh gas is coupled or decoupled from the venitlator?
it may be coupled (traditional or older machines are typically coupled but modern machines may be decoupled)
(piston ventilator is decoupled for sure)
How many pressure release valves does the piston ventilator have?
Two
One opens at +75 (give or take 5) cm H20
One opens at -8 cm H20
Which type of anesthesia machine automatically adds 2-3 cm H20 of PEEP?
gas- driven bellows automatically add 2-3 of PEEP due to the design of the ventilator spill valve but piston ventilators do not add PEEP in this way
When does the bag inflate and deflate in the piston ventilator?
inflates during inspiration and deflates during expiration (seems counter intuitive)
What mode on the ventilator are you using if the tidal volume is set?
volume control
What mode on the ventilator are you using if the airway pressure is set?
pressure control
