APEX: Anesthesia Machine and review test Flashcards
3 pressure systems of anesthesia machine
high
Intermediate
low
Cylinder pressure regulator part of what pressure system
high
Oxygen flush valve part of what pressure system
Intermediate
Flowmeter and common gas outlet part of what pressure system
Low
SPDD model stands for
Supply
Processsing
Delivery
Disposal
Match function with compoent Supply: Processing: Delivery: Disposal
Supply -> Vaporizer
Processing -> Circle system
Delivery -> Cylinder
Disposal –> Scavenging
Supply defines
location
how the gases enter the aneshesia machine; Pipeline to back of machine
Processing defines
Location
How anesthesia machine prepare gases before they are delivered to the patient.
Location : inside the machine up to the common gas outlet
Delivery defines
Location
How the prepared gases are brought to the patient
Location: Breathing circuits
Disposal defines
Location
How the gases are removed form the OR
Scavenging systems
5 tasks of O2
O2 pressure failure alarm O2 pressure failure device O2 flowmeter O2 flush valve Ventilator drive gas
Ventilator does not require a drive gas
A piston driven ventilator
Role of PISS
Prevent wrong cylinder from being attached to the anesthesia machine
Role of DISS
Prevent wrong gas hose from being attached to the anesthesia machine
Role of the SPDD
Pathway of gas through the machine
Not a function of the anesthesia machine
Filtering and exchanging air in the OR
What is different for each gas connected to the back of the anesthesia machine?
PIn configuration is different
What pressure change occurs with O2 entering the hanger yoke?
O2 cylinder pressure 1900psi drops to 50 psi upon entry to the intermediate system
What can allow for the PISS system to be bypassed?
The presence of one or more washer between the hanger yoke assembly and the stem of the tank
PISS configuration for O2 is
2, 5
PISS configuation for Air is
1, 5
PISS configuration for N2O is
3,5
Pipeline pressure and intermediate pressure system
50 psi
The bourdon pressure gauge on an oxygen cylinder reads 500 psi. if the flow rate is 2L/min how long will this cylinder provide oxygen to the patient?
87
Should the oxygen cylinder on the back of the anesthesia be on when not in use?
no. It should be turned off. Only on when you’re not using the oxygen from the pipeline.
The only way of determining cylinder content is by its _____not its _____
label; color
Max pressure of air tank is
1900psi
Max Liter of air tank is
625 L
Max pressure of O2
1900 Psi
Max liter of O2 tank is
660L
Max pressure of N2O
745 Psi
Max Liters of N2O
1590L
Weight of N2O when full is
20.7lbs
Weight of N2O when empty is
14.1 lbs.
Why does the calculating remaining L does not work with N2O tanks
N2O exists as both a liquid and a gas inside the cylinder. As long as the liquid remains in the cylinder, the partial pressure measure by the bourdon pressure gauge will remain 745
What is the significance of a decrease in the N2O tank pressure?
The pressure of N2O begins to decrease only after all the liquid is gone and only gas remains. At this point, the cylinder is about 3/4 empty, so approximately 400L of N2O remains in the tank.
What is the only reliable way to know the volume of N2o that remains in the tank?
Weight it
How should gas cylinders stored?
upright position. When changing the cylinder it’s ok to temporarliy place the old cylinder on its side until it can be moved
You should remove the _________before installing the cylinder
Remove the plastic cover
The fire triad consists of
Oxidizer
Fuel
Igniter.
Never to this causes it increase the risk of fire
Oiling the cylinder valve.
If there is a leak after you instal a cylinder, what should NOT be attempted?
Do not be tempted to place more than one washer between the cylinder and the hanger yoke assembly. This may bypass the PISS and allow the wrong cylinder to be matched up with the wrong hanger yoke assembly.
When is the OXYGEN pressure failure device activates? (2)
Oxygen tank is exhausted
Oxygen pressure in the supply line is less than 20 psi
The oxygen pressure failure device monitors ______not _____
pressure , not concentration.
When the FiO2 falls below 21 percent, what monitor that?
Oxygen analyzer monitors oxygen concentration
what happens when the pipeline pressure fails and the Auxilliary oxygen tank was left open, what will happen?
the oxygen pressure failure device wont activate until oxygen pressure is LESS THAN 20 PSI.
The oxygen pressure failure device is not activated by
pipeline crossover , or if a leak develops develops distals to the flowmeters.
Role of Oxygen pressure failure device: FAILSAFE DEVICE
Monitor and protect against low oxygen pressure in the anethesia machine.
It is the _______ in the oxygen supply line that is responsible for maintaining the fail safe valve in the open position
PRESSURE
Fail safe device resides in the
Intermediate pressure system
2 components of the fail safe device?
a) Alarm that sound when OXYGEN PIPELINE PRESSURE FALLS belwo 28-30 psi
b) A pneumatic device that reduces and or stops flow of N20 when pressure of Oxygen PIPELINE falls below 20 PSI
When O2 pressure drops below 20 psi, what does the fail safe valve does and what happens to N2O
Less pressure on the spring and will cause N2O flow to decrease proportionately or stop completely.
What is the only gas that passes directly from its source to its flow valve at the flowmeter?What happens to fail-safe valve before?
Oxygen ; all other gases encounter a fail safe valve before it enters its flowmeter.
Oxygen failsafe device for Datex ohmeda, what will stop the flow of N2O
O2 pressure less than 20 psi ; If O2 pressure >20 psi, N2O is allowed.
How can you tell the oxygen failure pressure safety device is working?
Turn on the oxygen and nitrous oxide flow. Next, make sure the back up oxygen cylinder is closed, and then remove the source of oxygen pressure by disconnecting the oxygen pipeline. As you removed the oxygen source, be sure to observe the flowmeters. The nitrous oxide flow should stop before the oxygen flow stops,. Reintroducing the oxygen supply to the anesthesia machine should result in both gases restored to their previous rates.
The hypoxia prevention safety device on the aneshesia machine will:
Limit the N2O flow to 3 times oxygen flow
What prevent a hypoxic mixture?
the hypoxia prevention safety device prevents you from accidentaly setting a hypoxic mixture with the flow control valves. It is a pneumatic or mechanical device that limits the nitrous flow to NO MORE THAN 3 times THE OXYGEN FLOW
Are the oxygen pressure device and the hypoxia prevention safety device the same thing?
NO
What limits the N2O flow to 3 times O2 flow
Proportioning device. (hypoxia prevention device)
The hypoxia prevention safety device prevents you from
Setting a hypoxic mixture with flow control valves. When you are giving N2o, the proportioning device ensures that Fio2 never drops below 25%.
Link 25 systems (GE- Datex Ohmeda)
If you adjust the flow control valve in such way that it would create a hypoxic mixture, a gear engages and oxygen flow is automatically increased.
Oxygen RATIO monitor controller does what?
supply of N2O is adjusted to maintain 3:1 ration
Datex Ohmeda proportion system is
LInk 25 systems
Drage proportion system is
Oxygen Ratio Monitor controller.
When can’t proportioning device can’t prevent a hypoxic mixture?
Oxygen pipeline crossover
Leaks distal to the flowmeter valves
Adminstration of third gas helium
Defective components
What is the annular space of the flowmeter tube?
The area between the WIDEST area of the INDICATOR float and side wall of the flowmeter.
The traditional flowmeter aka
Thorpe Tube
Thorpe tube measures
the fresh gas flow that travels towards the vaporizers and CGO
Flowmeter design : 3 main things to know?
Annular space
Internal diameter
Variable orifice
Flowmeter - Internal diameter
Narrowest at the base and WIDEST on TOP
Flowmeter: Variable orifice
provides CONSTANT GAS PRESSURE throughout a wide range of flow rates.
With the flowmeter , the position of the indicator float is determined by the 2 opposing forces:
The fresh gas flow pushes the indicator float up
Gravity pulls the indicator float down.
The flow measurement is taken at the
WIDEST part of the float
Flowmeter leaks can lead to ______why?
HYPOXIC MIXTURE . Because the flowmeters are distal to all safety devices except the oxygen analyzer
Key point about Flowmeters?
O2 Flowmeter should be positioned all the way to the right, (CLOSEST to the CGO). this minimize but DOES NOT ELIMINATE the risk of hypoxic mixture in the event of flow meter leak
The flow rate through the tube determines what 2 important characteristics of flow?
Whether the gas flow is LAMINAR or TURBULENT , and can be Predicted by REYNOLDS NUMBER
What determines if flow is laminar or turbulent?
Reynolds number (Re)
Re < 2000 is ______What does it depend on ?
Laminar (Dependent on Gas VISCOSITY (LV) Poiseuilles equation
Re>4000 is ______What does it depend on ?
Turbulent (DENSITY) - Graham’s LAW
Re 2000-4000
Transitional
Reynolds number formula
Density x diameter x velocity/ viscosity
Low fresh gas flow favor a _______flow
Laminar
Higher fresh gas flow favor a ______Flow
Turbulent
You are administering air 1L/min and oxygen 3L/min . Calculate the fraction of inspiredO2?
80
Formula to calculate Fio2?
FiO2 = (air flow x 21) + (Oxygen flow rate x 100) / total flow rate
You are using machine that couples fresh gas flow to tidal volume and fully compensates for circuit compliance. Calculate the total tidal volume delivered to the patient. Oxygen= 3L/min Air = 1L/min I:E = 1:2 Bellows = 500ml Respiratory rate = 10
632-633
Steps to calculate Fresh gas coupling
1. Convert fresh gas flow from L/min to ml /min (4L/m = 4000ml/min)
2. The I:E ratio is 1:2. Over the course of 1 min, the patient will spend 20 seconds in inspiratory and 40 seconds in expiration. Said another way, pt will spend 1/3 of the minute inspiring and 2/3 of the minutes expiring. Since only FGF during inspiration will be added to the TV set on the ventilator, multiples the total fresh gas flow by 1/3 or 33.33% (4000ml/min) x (1/3)= 1333 ml/min
3. The previous step established that over the course of a minute, 1333 ml will be added to the tidal volume. we need to calculate the TV per breath, so we divide 1333ml /10 breaths per min = 133 ml
4. Add the volume set on the ventilator to the FGF during inspiration (500 + 133) = 633ml
In summary;
(4000ml/min x 1/3) /10 = 133ml
133 + 500 = 633
All modern anesthesia when it comes to the FGF and TV
All modern anesthesia machine separates FGF from tidal volume., therefore the TV you enter on the ventilator is what the patient receives. Older machines couple FGF to the TV set on the vent, may lead to errors in predicted Vt and minute ventilation
With fresh gas coupling (FGF and TV )
(Vt set on ventilator) + (FGF during inspiration) - Volume lost to compliance.
If ask to factor in the volume lost to circuit compliance what should you do?
Substract it from 633ml.
Tidal volume increases with
Decrease RR
Increase I:E ratio (1:2 to 1:1)
Increase FGF
Increase bellows height
Effect of decrease RR on TV
TV increases
Effect of Increase I:E ratio (meaning from 1:2 to 1:1) on TV
TV Increases
Effect of increase FGF on TV
TV increases
Effect of increase bellow height on TV
TV increases
Effect of increase RR on TV
TV decreases
Effect of decrease I:E ratio (meaning from 1:2 to 1:3) on TV
TV decreases
Effect of decrease FGF on TV
TV decreases
how can you describe the relationship between RR and TV
Inverse relationship
decrease RR increase TV
Increase RR, decrease TV
Effect of decrease bellow height on TV
TV decreases
Relations ship of I:E ration, FGF and bellows height to TV
Direct relationship, increases or decreases, those decreases TV
Changs 4 thing will affect TV
FGF, bellows, RR and I:E ratio
Effect of Increasing FGF on TV, MV, PIP? what would you expect?
Increase TV, MV, and Peak Inspiratory pressure
Expect the end-tidal CO2 to decrease
Effect on Decreasing FGF on TV, MV, PIP? what would you expect?
Decrease TV, MV, and Peak Inspiratory pressure
Expect the end-tidal CO2 to Increase
Changes of FGF on TV and other parameters ONLY apply to
Old machine that couples FGF and TV
A ventilator is programmed to deliver a tidal volume of 600ml. if the breathing circuit compliance is 5ml/cmH2O and the peak pressure is 25cm H2O. what is the total volume that is delivered to the patient?
When ventilator creates PPV inside a breathing circuit not all the gas causes circuit to expand and does not contribute to the TV. Therefore
5cm x 25 = 125 (to calculate volume lost to the circuit) ——> 600- 125 = 475
Circuit compliance is a
Change in volume for a given change in pressure
Compliance = Change in Volume / Change in pressure
The isoflurane dial is set to 2%. What % of FG exiting the vaporizer chamber is saturated with isoflurane?
100%
Important concepts for variable bypass vaporizer (5)
Variable bypass Flow over Temperature compensated Out-of- circuit Agent specific
To fully understand the VARIABLE bypass concept, you must understand the _______What is the concept?
SPLITTING RATIO. when fresh gas flow enters the vaporizer , some of it encounters the liquid anesthetic, while the rest of it bypasses the anesthetic liquid. Before leaving the vaporizer, the TWO FRACTIONS mix and determine the final anesthetic concentration
So when speaking of splitting ratio , what happens when you set a higher or lower concentration on the dial?
More FGF towards the volatile agent, while setting a lower concentration direct less fresh towards the liquid anesthetic.
When the FGF enters the vaporizer chamber and FLOWS OVER what happens? What is needed for a CONSISTENT VAPORIZER OUTPUT?
bunch of turbullence and surface area is increase to make sure the fresh gas inside the vaporizer comes into contact and become 100% saturated with agent. Full saturation is NEEDED to guarantee a consistent vaporizer output?
What can REDUCE Vaporizer output (2)?
Flow less than 200ml/min or GREATER than 15L/min.
What can happen if the vaporizer is tipped over?
Its possible that some of the liquid anesthetic will enter the bypass chamber. this can increase vaporizer output.
1ml of liquid anesthetic produces
200 ml of anesthetic vapor.
What are your actions if the vaporizer is tipped?
RUN a high FGF through it for 20-30 minutes before it can be used for patient.
Define the latent heat of vaporization?
Number of calories need to convert 1 g of liquid into vapor WITHOUT a change in temperature.
What is carried away by vaporized molecules and how is this significant?
Heat is carries away by the vaporized molecules, and this causes the anesthetic liquid to COOL. COOLING DECREASE VAPOR PRESSURE and ultimately VAPOR OUTPUT
What prevent cooling after the vaporized molecules passes the vaporizer?
The temperature compensating valve adjusts the ratio of vaporizing chamber flow to bypass flow and guarantees a constant vaporizer output a wide range of temperature
Describe the TEMPERATURE COMPENSATING VALVE
Bimetallic strip
Variable bypass vaporizers are _____Specific
Agent
What is the significance of the pumping effect?
It can increase Vaporizer output.
What can cause the pumping effect?
Anything that lets gas that had already left the vaporizer to RE-ENTER the vaporizing chamber
2 things that generally cause the pumping effect
Positive pressure ventilation
Use of Oxygen flush valve
What enhances the PUMPING EFFECT (more pumping effect)
Low fresh gas flow
low concentration dial setting
Low level of liquid anesthetic in the vaporizing chamber.
The pumping effect is minimized by modern vaporizer desing
What is the most common CAUSE of a vaporizer leak?
Looser filler cap
What is the most common LOCATION of a vaporizer leak?
Internal leak in the vaporizer.
When is the only time a VAPORIZER leak can be detected?
When the vaporizer is turned on because it is functionally removed from the low pressure system when it is turned off.
HOw can you calculate how much liquid anesthetic is used?
ml of liquid anesthetic used per hour = Vol % x FGF (l/min) x3
This vaporizer does not use a flow-over design?
TEC-6 Desflurane
The desflurane vaporizer : the chamber that contains the anesthetic agent is pressured to _______and heated to ______
2 atm and heated to 39C
Relationship of TEC 6 Vaporizer OUTPUT with elevation?
Vaporizer output varies INVERSRSELY with elevation. Therefore , should be calibrated when its going to be used in high altitude locations.
What are the 2 vaporizes APPROVED for the use of desflurane?
TEC 6 Datex ohmeda
Drager D-vapor
What is the diffference between the variable bypass vaporizer and the TEC 6 ?
The variable bypass vaporizer directs a certain amount of fresh gas flow towards the liquid anesthetic , the TEC 6 injects a precise amount of vaporized Desflurane into the FGF.
Why does Desflurane different and require a specialized vaporizer? (2)
- signifcantly LESS POTENT than its peers
2. VP close to atmospheric pressure
Desflurane MAC is _____while sevoflurane MAC is ______ and isoflurane MAC is ____-
6.6; 2; 1.2
To achieve the same depth of anesthesia, the absolute volume of desflurane that vaporized is (higher/lower)
HIGHER
Remember heat is carried away as the vaporized molecules leaves the chamber, what solves this problem ?
Heating and pressurizine the TEC 6 to 39C and 2 atm respectively
Desflurane bolis, at, above or below rooom tem
above 39C (room temp is 22)