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)
Remember, The fresh gas that goes through the variable bypass vaporizer is
SPLIT
The HIGH vapor pressure of the desflurane would ? What solve the issue?
require a bypass flow beyond the limits of the anesthesia matching to dilute desflurane to a clinically useful concentration. AN INJECTOR DESIGN
Those types of vaporizer not affected by change in elevation?
Variable bypass vaporizers.
Does not compensate for changes in elevation
TEC 6
What determines the depth of anesthesia?
The partial pressure of VA in the brain
At higher elevation, the concentration exiting the vaporizer will be
Whatever you set on the dial. BUT, since atmospheric pressure is LOWER at elevation, the partial pressure in the breathing circuit will be lower.
At a lower elevation or HYPERBARIC CHAMBER, the concentration exiting the vaporizer will be
Whatever you set on the dial. BUT, since atmospheric pressure is LOWER at elevation, the partial pressure in the breathing circuit will be HIGHER
How do you calculate the vaporizer output at elevation?
Required dial setting = Normal dial setting (% x 760mmhg)/ ambient pressure (mmHg)
A LOWER ambient pressure is _______altitude
HIGHER
A HIGHER ambient pressure is
hyperbaric oxygen
A lower ambient pressure requires a
HiGHER SETTING on the dial (HIGH altitude)
A higher ambient pressure requires a
LOWER SETTING on the dial
Position of vaporizer in relation to circuit
OUT of circuit
Method of Vaporization for TEC 6
Gas vapor blender, heat creates a vapor that is injected into the fresh gas
Method of Vaporization for Variable bypass
Vaporizer splits fresh gas.
What is the first and second to detect an oxygen pipeline crossover
OXYGEN ANALYZER
PULSE OXIMETER
What are the MOST CRITICAL and KEY actions that should be carried out in the EVENT of an OXYGEN PIPELINE CROSSOVER?
Turn on the oxygen tank
Disconnect the pipeline supply
When the oxygen analyzer alarm sound? What is best to assume?
Pipeline crossover as occurred until other causes can be ruled out.
Trust this and do not attempt to fix it when occurs
Oxygen analyzer
Take home is whenever you switch to the oxygen cylinder, you must
Disconnect the pipeline
After you disconnnect from the pipeline and put the patient on the tank, verify
that the O2 concentration is increasing, if not, AMBU bag patient. Use low flow if convert to tank. Call for help.
The O2 Flush valve delivers a continuous oxygen flow of
35-75 L/min at 50 PSI (pipeline pressure)N
2 true statement about the O2 flush valve
Excessive use can lead to awareness
The risk of barotrauma is minimized by venilators with fresh gas DECOUPLING.
Taught not to use O2 FLUSH VALVE WHEN patient on ventilator on OLD machine, why is it IRRELEVANT for newer machines?
During inspiration, the ventilator drive gas closes the VENTILATOR spill valve. Therefore, pressing the O2 Flush valve does not affect this function.
What is the flush valve function? What does it bypass?
Provide a path for O2 to travel from the intermediate pressure system to the breathing circuit. Bypasses the low pressure system
This with the O2 flush valve can lead to barotrauma? why?
Pressing the O2 flush valve during the INSPIRATORY cycle can lead to barotrauma. Because the spill valve is closed during inspiration, pressing the O2 flush valve would expose the breathing circuit and the patient to 50 psi and an oxygen flow rate of 35-75ml.min.
It is critical that you do not do this during inspiration when the patient is on the ventilator
DO not press the oxygen flush during inspiration.
What are the 2 functions of the drive gas of a pneumatic ventilator?
Compresses the bellows
Opens and closes the ventilator spill valve.
What happens to the drive gas during inspiration? and why?
The drive gas closes ; to make sure the TV gets to the patient and not to the scanvenger.
What happens to the drive gas during expiration? and why?
The flow of the drive gas stops.
The EXHLAED TV first refills the bellow and after the circuit pressure exceeds, 3cm H2O, the spill valve open and excess gas goes out of the scavenger.
FGF is continuously
added to the breathing circuit.
The amount of air going to the bellows is
the sum of TV + flowmeter flow during expiration .
Action of drive gas on inspiration
Drive gas compresses bellows
Drive gas closes spill valve
FGF from vent goes to patient
Action of drive gas on EXPIRATION
Expired gas refills the bellow
Bellows fills completely
When circuit pressure > 2-4 cmH2O, expired gas is directed through the spill valve to the scavenger.
Anesthesia machine minimize the risk of barotrauma by
isolating tidal volume delivers by the ventilator from the flowmeters and oxygen flush valve. this is called gas decoupling. In the vents, what is set on the vent is what is actually delivered to the patient
Preventing barotrauma also done by the_______how is it done?
Inspiratory pressure limiter can limit the breathing circuit during inspiration. When the breathing circuit pressure rises above the set point, the excess gas is vented out the scavenger. you can think of the inspiratory pressure limiter as an APL valve that affects the ventilator.
How can pushing the O2 flush valve lead to awareness?
The gas from the oxygen flush does not pass through the vaporizers, excessive use of the oxygen flush valve adds gas to the breathing circuit that does not contain volatile anesthetics. As a result, it dilutes the partial pressure of volatile agent and may lead to patient awareness.
Stuck open flush valve will result in
barotrauma
Pneumatic bellow, hole in the bellows lead to
Barotrauma
Pneumatic bellow, leak in the bellows lead to
may cause the reading on the oxygen analyzer
If there is a bellows leak and oxygen is used as the ventilator drive gas, the FiO2 in the breathing circuit.
may increase
Remember the ascending and descending bellows have “e” in the word meaning that they inflate during
Expiration
Ascending bellows rise during
Expiration
Will ascending bellow fill if there is a disconnection? what about when there is a leak?
NO; only partially will
Which one is safer, ascending or descending?
Ascending
Descending bellows falls with
Expiration
What is the problem with descending bellows?
May continue to rise and fall if there is a circuit disconnect. Gravity cause it to fall during expiration.
Newer machine decouples
TV from fresh gas flow
What can happen when there is a leak in the bellows>
High gas pressure to the breathing circuit., high pressure in breathing circuit may cause barotrauma.
If the ventilator drive gas uses air or an air-oxygen mixture and you are running high FIO2, then a hole in the bellows will cause FiO2 to
Decrease
The piston ventilator is a
compresses by an electric motor.
What does the piston ventilator does not do?
Doesnt use oxygen as a drive gas so it won’t consume to oxygen in the event of oxygen pipeline failure.
In a piston ventilator, is TV coupled with FGF? what about TV? what about barotrauma ?
NO. Allows for more precise delivery of TV. FGF is decoupled from the ventilator.
IT remains a risk
The vent of anesthesia machine comes in 3 varieties what are they
Piston
Ascending bellows
Descending bellows
3 types of machine with piston vent
Apollo
Fabius
Narkomed 6000
Pneumatic bellows need this to compress bellows
oxygen to compress bellow during mechanical ventilation
Pressure relief valves in the piston ventilator are
Positive and negative pressure.
On the piston vent, when does the positive pressure relief valve open? What does that prevent?
75 +/- 5 cm of H2).
Prevent pressure build up in the anesthesia circuit.
On the piston vent, when does the negative pressure relief valve open? What does that prevent? And why is it important to the patient?
8 cm H2O. when pressure in the circuit falls below this value, the negative pressure relief valve open and let room air enter. Protect against negative end-expiratory pressure (NEEP_.
Fresh gas Decoupling and piston ventilator
Piston vent decouples FGF from the vent and they deliver a consistent tidal volume regardless of the changes made in the fresh gas flow, RR, or I:E ratio. Many other vents, change in FGF, RR and I”: E will affect TV delivered to the patient
PEEP and PIston
Gas-driven bellows automatically add 2-3 cm H2O peep , due to the design of the vent spill valve.
PISTON vent: Breathing bag inflates during
Inspiration and deflate during expiration.
With the PISTON vent: if the breathing bag quickly become deflated you should suspect
a circuit disconnect. The piston will not move when a patient initiates spontaneous breaths while on the vent.
Pressure control ventilation , gas flow with inspiration
Decelerate
Risk of ventilator associated injury is decrease with
PCV
In pressure control ventilation, because the peak pressure is _______ and the Tidal volume is __________ and increase in lung compliance will ______Tidal volume
Fixed
variable
increase
During the pressure control ventilation, vent achieves a peak pressure very early in the inspiratory cycle and
Hold it for a time determined by the I:E ration, it does not cycle immediately after the pressure is achieved.
OR vents cycle between
Inspiration and expiration over a set period of time
With OR vent, What happens during inspiration?
The inspiratory flow continues until a specified TV or airway pressure is achieved
If the TV is set, you are using a
Volume controlled mode, and
If the airway pressure is set, you are using a
Pressure controlled mode. Some machines blend these approaches
Volume controlled Ventilation (VCV)
Delivers a preset TV over a time predetermined. The TV is fixed, the inspiratory pressure will vary as the patient’s compliance changes. Inspiratory FLOW IS constant during inspiration
Pressure controlled Ventilation (PCV)
PCV Delivers a preset inspiratory pressure over a time predetermined. Since the pressure and time are fixed, the TV and the inspiratory flow will vary depending on the patient’s lung mechanics. If airway resistance rises or lung compliance decrease, TV will supper and a higher inspiratory flow will be required to achieve the preset airway pressure.
Volume controlled FIXED parameters are (VIIT)
TV
Inspiratory flow rate
Inspiratory time
Volume controlled VARIABLE parameters are
Peak inspiratory pressure
Pressure controlled FIXED parameters are
Peak inspiratory pressure
Inspiratory time
Pressure controlled Variable parameters are
TV
Inspiratory flow
What are the advantages of PCV in terms of TV
Delivers larger TV for a given inspiratory airway pressure.
What are the advantages of PCV in terms of gas exchange
Improves gas exchange
What are the advantages of PCV in terms of Lung injury
Reduces
When is PCV useful
Pt has low compliance
High PIP is dangerous
Compensate for leaks
What are the disadvantages of PCV
Increase airway resistance and/or decrease lung compliance reduce TV
PCV mode requires extra attention with circumstances that can
alter pulmonary resistance or compliance, as they will cause the TV to change.
Remember what is compliance again?
Lung compliance, or pulmonary compliance, is a measure of the lung’s ability to stretch and expand (distensibility of elastic tissue).
Compliance: In clinical practice it is separated into two different measurements,
static compliance and dynamic compliance.
4 Low compliance patient conditions
Pregnancy
Obesity
Laparoscopy
ARDS
High PIP dangerous in those situation
LMA
Neonate
EMPHYSEMA
Compensate for leak
LMA
Uncuffed ETT in children
VT decrease with
Decreased compliance
Increased Resistance
What occurs with compliance with Pneumoperitoneum ?
tredelenburg position ?
Decrease compliance can occur
What happens with resistance with Bronchospasm? kinked ETT?
Increase resistance
VT increase with
Increase compliance
Decrease resistance
What occurs with compliance with release of Pneumoperitoneum ?
going from tredelenburg position to supine ?
Increased compliance
2 things that may cause decreased resistance
Bronchodilatory therapy
Removing airway secretions
No matter what mode of ventilation is used, what indicates a spontaneous breath?
A negative deflection just before the breath
No matter what mode of ventilation is used, what indicates a machine initiated breath
Positive deflection
Modes of ventilation BEST SUITED for LMA?
SIMV
PSV
Modes of Ventilation , BEST SUITED for patient who don’t have a respiratory drive
CMV
IMV
Controlled MANDATORY VENTILATION (CMV) What happens with TV , and RR
Machine initiated breath delivers a preset TV and RR on a fixed schedule
Does CMV compensate for patient’s intimated breath?
No
Best mode for apnea patients
CMV
Assist Control (AC) what happens with TV and RR
Machine initiated breath delivers a preset VT and RR
AC: Spontaneous breath receive
Full preset TV , meaning the TV will be the same if the machine or the patient initiates the breath
What is a patient that OVERBREATHES the vent at risk for ?
Hyperventilation and respiratory alkalosis
SIMV : what happens with TV and RR
Machine initiated breath delivers a preset VT and RR, but this mode let the patient breathe on its own in between the machine initiated breaths.
During SIMV, if the patient breathe before a machine breath is due, what happens to the timing of the machine breath
It will adjust to coordinate with the patient’s spontaneous breath (synchronized)
SIMV promotes
better synchrony between the patient and the ventilator
Spontaneous breaths can be augmented with what support ?
Pressure support
SIMV guarantees a minimum
MV. The more the patient work, the less assistance the ventilator give the patient. The less the patient work, the more assistance the vent give the patient.
SIMV useful with
weaning or with an LMA
PCV-VG stands for
Pressure Control ventilation with Volume Guarantee
Sometime you use PCV and realized patient’s TV changed drastically, why? Seen with what kind of procedures?
Because of compliance changes seen with laparoscopic surgery or in response to surgical positioning.
PCV- VG gives you what benefit?
PCV with a guaranteed predetermined TV while applying the minimum pressure required to deliver that TV
Pressure SV ventilation
Augment the patient’s spontaneous breath, unless the ventilator provide a back up rate if apnea is detected (PSV-PRO)
PSV-PRO means When the patient’s is on PSV and apnea is detected what happens
The vent provide a back up rate if it detect apnea
CPAP is a
continuous pressure is applied to the breathing circuit throughout the respiratory cycle.
2 benefits of CPAP are
Augment patients spontaneous breath
Reduces airway collapse during expiration
CPAP there is nothing during
EXPIRATION
BIPAP is a
2 level of pressure are set.
BIPAP Pressure 1
Inspiratory positive airway pressure (think pressure support for a spontaneous breath.
BIPAP pressure 2
Expiratory positive airway pressure (think CPAP during exhalation )
BIPAP stands for
Biphasic positive airway pressure
BIPAP is the pressure receive on inspiration same as on expiration?
NO; patient receives a set pressure on inspiration and a different kind of pressure on expiration.
APRV stands for
Airway pressure Release Ventilation (APRV)
APRV is used for
spontaneous ventilation .
APRV provide a high level of
CPAP throughout most of the RESPIRAtory cycle. and the pressure is released at preset intervals to facilitate exhalation
APRV useful in patients with
ARDS
IRV stands for
Inverse RATIO ventilation
IRV, the I:E ration determines
How much times is spent in each part
With most modes ventilation Insp is
inspiratory shorter than expiratory
IRV reverses the
Inspiratory vs expiratory ration, MORE TIME is provided for inspiration .
IRV requires the patient
Paralyzed and sedated
IRV useful in patient with
Small FRC
ARDS
Risk of IRV
Dynamic hyperinflation (auto-peep or breath stacking)
What is high frequency ventilation vs Conventional modes of ventilation?
Conventional mode Delivers TV that exceeds anatomical dead space where as high frequency ventilation delivers a TV below anatomic dead space in conjunction with a very high RR.
Types of High frequency ventilation
High frequency oscillation, jet ventilation, high-frequency percussive ventilation.
What is the dye that indicates when the soda limes exhaust?
Ethyl violet
When does Ethyl violet changes from colorless to purples
When pH falls below 10.3
What is the role of the CO2 absorbent?
remove Co2 from the breathing circuits.
CO2 reaction is an examples where
a base neutralizes and acid
CO2 absorbents allow for
conservation of anesthetic gases /
Write the 3 step of CO2 Reaction with soda lime
- CO2 + H2O –> Carbonic acid (H2CO3)
- H2CO3(carbonic acid) + 2 NaOH (Sodium hydroxide NaOH) –> Sodium Carbonate (Na2CO3) + 2 Water + HEAT
- Sodium Carbonate (Na2Co3) + Calcium hydroxide (CaCo2) + 2 Sodium Hydroxide(NaOH _
Mesh size must be a balance between
Surface area and airflow resistance
Small granule have _______surface are with ______resistance
High; High
Large granule have_____surface area and _____resistance
Low; Low
Mesh size are
4-8 mesh , this combination of absorptive capacity and airflow resistance
2 major problems that can occur with the CO2 absorbents?
Absorbent exhausted(Can no longer neutralize Co2) Absorbent desiccated(dry)
Ethyl violet of an exhausted CO2 absorbent may return to white after being purple, but that does not indicate
the CO2 absorbent can be used again.
In the presence of exhausted soda lime, the anesthetist should
Increase MV. Does not prevent hypercarbia
If anesthetist unable to replace Co2 Absorbent,
Increase FGF to convert circle system into a semi-open system. This will prevent rebreathing and the baseline on the capnograph should return to zero.
What is required to facilitate the reaction of Co2 absorbent
Water.
Desiccated soda lime increases the production of
Carbon monoxide in the presence of halogenated anesthetics and compound A in the presence of Sevoflurane
CO may cause and Compound A may cause
Carboxyhemoglobinemia and compound A may cause renal dysfunction
What is the most UNSTABLE halogenated anesthetic in the presence of a soda lime?
Sevo
Methods to decrease the risk of CO and compound A
low fresh gas flow to preserve water content of the soda lime
Turn off fresh gas flow between case
Change absorbent when exhausted
When compared to soda lime, what factor is increased with the use of calcium hydroxide lime (Amsborb plus)
Frequency of replacement.
Benefits of calcium hydroxide lime (absorb plus)
No CO produciton
Very little to no compound A
Lower risk of fire compare to soda lime
Drawbacks of calcium hydroxide lime
Lower Co2 absorpition capacity
More frequent replacement needed
Higher cost.
What is the most common cause of a low circuit pressure?
Circuit disconnect.
What is the SECOND Most common cause of low circuit pressure
Leak around the CO2 absorbent.
Sources of low pressure breathing circuit
Circuit disconnect Defective Co2 absorbent canister Leaks around absorbent canister Malfunction of bag/valve switch Incompetent spill valve Leaks
4 ways to Monitor for circuit disconnect are
Pressure
Volume
ETCO2
Precordial stethoscope
Visual inspection of chest rise
Capnography
The only thing that monitors the concentration of O2
Oxygen analyzer
If unable to ventilated due to low pressure,
Ventilate with ambu bag, and O2 tank while providing TIVA.
Which monitor will detect a circuit disconnect first?ask those questions
- will monitor alert you in real time or there is a delay? Anything ELECTRONIC WILL HAVE A DEALY.
- If all the monitors have some degrees of delay , which one is the shortest?
During GA with ETT , the high peak pressure alarm sound, after changing switch from vent to bag, the peak insp pressure returns to baseline. What is the explanation for that?
Vent spill valve malfunctioned.
Consequence of elevated breathing circuit pressure as far as venous return, CO, BP,
Decreased VR, CO, and Hypotension occur.
Elevated breathing circuit pressure and sequelae of things
Pneumothorax SC emphysema Death CV collapse. Barotrauma
If PIP rises what should you check first
Patient related causes
PIP rises chief amount patient related causes is
Bronchospasm
When PIP alarms goes off: If you remove the patient from the ventilator and the circuit pressure return to baseline what is the likely explanation
Ventilator spill valve failed.
What is the function of the spill valve?
To vent excess fresh gas flow FROM the Flowmeters to the SCAVENGER. If the valve fails, the extra fresh gas flow will have nowhere to go and there will be high circuit pressure which will alarm the PIP high sounds
When high PIP alarm goes off, If you remove the patient from the ventilator and the circuit pressure remain elevated, what is the likely explanation
Scavenger is occluded OR positive pressure relief valve on the scavenger have failed. You may remove the scavenger transfer tubing from the APL valve
If you can’t, just ventilate patient with AMBU and begin TIVA
Other causes of High pressure include
Not removing plastic wrap from CO2 absorbent/ anesthesia mask, malfunction of PEEP or expiratory unidirectional valve.
While a patient is ventilated sponteaneously with an ETT, you notice the FGF of 10L/min is required to fill the breathing bag and see that the scavenger system is not working, which statement must be true?
The negative pressure relief valve has failed.
Scavenger system can be
Active or passive
Active scavenger means,
Active system use suction
Passive scavenger relies on
Positive pressure of fresh gas leaving the interface.
Scavenger can be ____Or open
Closed or open system.
A closed scavenger system uses_____and open scavenger is
Valve; Open to the atmosphere.
For the scavenger system, when the negative pressure relief valve fails,
Its possible or the vacuum to remove gas from the breathing circuit
For the scavenger system, when the positive pressure relief valve fails,
FGF accumulates inside the breathing circuit, this can cause barotrauma.
2 function so the scavenger syst
Remove excess gas from the anesthesia circuit
Minimize environmental exposure to waste anesthesia gas
The most critical component of the scavenger is the
Interface.
Removal of too much gas from scavenger would cause a
negative pressure in the circuit .
Removal of too little gas from scavenger would cause
Barotrauma
With spontaneous ventilation, what control the amount of gas that remains in the circuit and the amount that is release to the scavenger?
APL
With mechanical ventilation, what control the amount of gas that remains in the circuit and the amount that is release to the scavenger?
Ventilator’s spill valve.
What are the 5 components of the scavenger system?
Gas collecting assembly Transfer tubing Interface (open or closed) Gas disposal tubing Gas disposal system.
Open system scavenger can only be used with
Active system
Risk of exposing OR personnel to was gas is higher with
OPEN system
This kind of scavenger interface contains a reservoir?
Close systems
Active disposal uses
suction to remove gas.
Nitrous alone ppm
<25
Halogenated agents alone ppm
<2
Halogenated + N2O ppm
<0.5
Determinants of Exposure to Waste Gases
Amount of OR vent and air turnover
Function status of Anethesia equipment
Practice as a CRNA
What is the water content of the soda lime?
15%
Components that create the greatest resistance to flow?
Endotracheal tube (smaller diameter)
Resistance is
8 x viscosity x length/ Pi x radius^4 x pressure difference
The combination of baralyme and sevo can lead to
FIRE
According to the WHO, O2 tank should be painted
White
Which action reduced compound A production ?
Removal of NaOH
Addition of Ca(OH)2
High pressure 3
Back up cylinder, cylinder yoke and gauge , cylinder regulator
Low pressure 3
Floswmeter, vaporizers, CGO, check valves
Intermediate pressure
Pipeline inlet, check valve, Oxygen 2nd stage regulator.
When the ambient temperature is increase, the bi-metallic strip in a variable bypass vaporizer direct
Less fresh gas to the vaporizing chamber
More fresh gas to the bypass chamber.
