Classification of Ventilators Flashcards
Power Input
What we plug in
Can be electrical, pneumatic, manual (not used anymore)
Power Conversion
Where the vent converts the plugged in power to a type that will be used to ventilate the patient
Can be a drive mechanism or a output control variable
There are two goals of the power conversion and transmission
1) Generate force necessary to deliver gas to patient
2) Regulate the deliver of said gas
Control System (Modes)
Where the specific mode and parameters is selected
Breathing Pattern-Control variable and breath seqence
Control Types-Tactile Control (within breaths), strategic control (between breaths), and inteligent control
Specific Control Strategy-Phase varaible, operational logic (conditional variable and performance)
Output Control
Where the mode and breath is delivered to the patient
Control Pressure Waveform
Display
Modes You Can Be In
CMV-PC CMV-VC CMV-PC Adaptive IMV-PC IMV-VC CSV-PC CSV-VC
Types of Alarms
Input Power
Control Circuit
Output Power
Electrical Vents
Relies solely on electricity to function
This is usually from a wall outlet but can also be from a battery
Can only provide an FiO2 of 0.21 as to get a FIO2 > 0.21 there must be a pneumatic oxygen input
Where are Electrical Vents Used
Acute Care-Servo-i with compressor
Transport-LTV 1000
Home Ventilator-LP 20
Pneumatic Vents
Does not plug into an outlet (does not need electricity to function)
Relies solely on compressed gas to function
An advantage is that is can be used in environments where there are no electrical sources permitted/available
A disadvantage is that it uses a lot of gas and that you can not be as detailed in your settings (all or nothing)
When are Pneumatic Vents Used
Remote Location
Transport
MRI
Combined Power Input Vents
Requires both an electrical source (wall outlet or battery) and pneumatic source to function
Most modern critical care ventilators are electrically and pneumatically powered
Examples: Dräger Evita 4, Puritan-Bennet 840, Maquet Servo-i
Power Conversion-Drive Mechanism
Converts power into useful work
Direct regulation from a compressed gas source (Evita 4, Servo-i, Servo 300)
Compressors (LTV 1000 turbine compressor, NPB 7200 & Servo-i have optional compressors)
Spring loaded bellows (Servo 900C (older ventilator))
Motor and linkage-Rotating crank and piston (LP 20) or Motor/rack and pinion
Output Control Valves
Regulates the flow of gas to the patient
You always need an exhalation valve in a ventilator circuit
Types of Output Control Variables
Simple on/off exhalation valves-Pneumatic diaphragm, Gate valve, Active exhalation valve
Flow control valves-May open/close completely (On/Off) (Electromagnetic poppet valve) or may open/close in small increments (Proportional solenoids-most modern ventilator will use these for flow)
Most modern ventilator will use a combination of both
Control Circuit
In order to control pressure, volume, flow, or time the ventilator must have a control circuit
Can be mechanical, pneumatic, fludic, elctrical, electronic/microporcessor
Often ventilators will combine two or more of these subsystems
Modern ventilators are usually microporessed controlled
Control Circuit-Mechanical
Uses pulley, levers, etc
Used in early ventilators but not used today
Control Circuit-Pneumatic
Porvided using gas power
Pressure regulators, needle valves, het entrainment devices, balloon valves
Used in transport ventilators
Control Circuit-Fludic
The main advanatge is that there is no moving parts so that technically it can be sued forever
It not cause any electronic interference and therefore can be used in an MRI
Monaghan 225 is a purely fludic ventilators (pneumatically powers)
Disadvantages- Uses a lot of gas, unable to fine tune breaths
Breathing Pattern Control Variables
The control variable is the physical parameter that is manipulated by the ventilators
The follow are the types of control variables and only one can be used at a time
1) Pressure
2) Volume
3) Time (uncommon)
Pressure Controlled Ventilation
Considered to be pressure-controlled or pressure-limited when the vent keeps the pressure waveform in a specific pattern
The pressure delivered (and thus its waveform) is unaffected by changes in the patients resistance and compliance
Thus, the shape of the volume and flow waveforms depends on the pressure waveform and the patients lung characteristics
Volume Controlled Ventilation
When you are controlling the volume you will also be controlling the flow (and vice versa)
The equation for flow is volume over time which is why you also control time when you are in a volume/flow control
The volume and flow delivery are unaffected by changes in pt’s lung characteristics
The pressure waveform will vary depending on the pt’s lung characteristics
The less compliance in the patient’s lung the more time it will take to fill the lungs
Continuous Mandatory Ventilation (CMV)
This is full ventilatory support meaning that every breath is controlled by the vent and will be the same
Type of Breath Sequences
Continuous Mandatory Ventilation (CMV)
Intermittent Mandatory Ventilation (IMV/SIMV)
Continuous Spontaneous Ventilation (CSV)
CMV Breath Types
Every breath is considered to be a mechanical breath, but there is two different types of breaths that can be delivered
- Mandatory: Ventilator initiated
- Assisted: Patient initiated and then the vent will take over to make sure the exact type of breath wanted is deivered
We have a patient that is on a ventilator in CMV mode and set to 12 breaths/min and the patient breathing at 16 breath/min.
a) What type of breaths are being delivered
b) What is the pt. is now only breathign 11 b/min
a) The ventilator will deliver 16 mandatory assisted breaths to the patients. If in volume control then these breaths will be to a set volume. If it is in pressure control these breaths will be to a set pressure
b) The ventilator will deliver 11 mechanical assisted breaths and 1 mechanical mandatory breath
Intermittent Mandatory Ventilation (IMV/SIMV)
The goal is to deliver a set number of mandatory breaths and the patient can breath above the set rate with spontaneous breaths
Generally there is a window in which the patient can trigger a breath and if the patient doesn’t make the effort then a mandatory breath will be delivered at the end of the window
This means that in SIMV can be mandatory, assisted, and spontaneous breaths
Example: The ventilator is set IMV on a rate of 12 b/min, and the patient is breath at 16 b/min
a) What type of breath are they getting?
12 are mandatory assisted breaths and 4 are spontaneous breaths
Continuous Spontaneous Ventilation (CSV)
All breaths are spontaneous
They can be supported or unsupported by the ventilator
Breath Types in Controlled Mode
Mechanical Breaths only
The mechanical breaths can be VC, PC, or PRVC
Breath Types in CMV Mode
Mandatory and Assisted Breaths
Breath Types in IMV Mode
Mandatory and Spontaneous Breaths
Breath Types in SIMV Mode
Mandatory, Assisted, and Spontaneous breaths
Breath Types in CSV Mode
Spontaneous breaths only
Mechanical Breaths
Also known as mandatory breaths
Breaths initiated and controlled by vent
Breaths are time triggered
Controlled Mode
Not used often clinically as it does not allow for pt. efforts
What else do you need to set when you have pt. triggered breaths
Also have to set a sensitivity
CMV Indications
Pt. needs full vent support but are also trying to breath on their own still
Often inital mode in crisis management
Advantage of CMV
Can deliver a minimum rate, and pt is able to set there own rate as well
Will synchronize with pt. efforts
Dependign on breath type can guarentee a pressure or volume
disadvantage of CMV
If RR too high can result in respirtory alkalosis
Can increase pt. work if sensitivity not set correctly
Poorly tolerated in awake pt.
B/c the vent is doing a lot of the work there may be resp. muscle atrophy
Higher MAP
Cause/worsen auto PEEP
CMV
Delivered both mandatory and assistented mechanical breaths
Also called Assist/Controlled (A/C)
Can be CMV-VC, CMV-PV, CMV-PRVC
Assisted Breaths
Mechanical breath
Triggered by pt. but the rest is controlled by the vent
Spontaneous Breath
Triggered and cycled by pt.
Can be supported or non-supported
Non-Supportive Spontaneous Breath
The breath is triggerd, limited, and cycled by patient
Resp muscles take all repsonsibility for breathing
Triggering in CMV
Can be pt (assisted) or time (mandatory)
Trigger
Mechanism used by vent to initiate the start of inspiration
Possible Triggers
- Manual- Button on vent that allows operator to manually trigger a breath
- Time
- Patient-Pressure, flow, volume
Time Triggering
Breath wil be riggered after a certain period of time
Because the time period is set on the ventilator through the RR it is a mandatory breath
Ex. If the RR is set at 12 b/min then the vent will deliver a breath every 60/12 =5 seconds
So 5 seconds is the time trigger for a breath
Controlled Mandatory Ventilation- Volume Control (CMV-VC)
- Trigger
- Patient
- Time
- Limit
- Flow
- Cycle
- Volume
- Baselines
- PEEP
CMV-VC
Trigger-Patient or time
Limit-Flow
Cycle-Volume
Baseline-PEEP
CMV-PC
Trigger-Time or Pt.
Limit-Pressure
Cycle-Time
Baseline-PEEP
IMV/SIMV
Older ventilators in the IMV mode will deliver mandatory breaths regardless to patients efforts (unsynchronized to patient’s breathing), and this still may be used neonatal
New ventilators always are synchronized to patients’ breathing. Thus the “S” for synchronization is dropped by the modern classification system. You still may sometimes need to use the SIMV designation.
Ex. A patient is on the old version of IMV-VC with a RR of 10 and Vt 500 mL
This means that every 6 seconds (10/60) there will be a breath of 500 mL, and this breath will be delivered regardless of if the patient is already in the middle of a spontaneous breath
This can result in ‘breath-stacking’ and asynchrony-both which cause pressures in the chest which magnifies all the negative physiological effects of PPV
The patient however can make spontaneous efforts in between these 6 seconds
IMV Advantages
Variable amount of WOB for the patient
Can be used for weaning
May reduce the alkalosis assoc’d with A/C
Limits respiratory muscle atrophy
Lower MAPs
IMV Disadvantages
pt work if sensitivity not set appropriately
PaCO2, fatigue and tachypnea if RR set too low
WOB for S breaths unless PS is added
Continuous Spontaneous Ventilation (CSV)
A mode that is purely spontaneous, meaning that there is only spontaneous
Continuous Spontaneous Ventilation (CSV) Breath Types
Spontaneous Unsupported Breath (CPAP)
- Requires a baseline to be set
- The patient breathes at this elevated baseline
- RR, TI, Vt are the direct result of patient efforts
Spontaneous Supported Breaths
- Requires a baseline pressure to be set and for a support level to be set
- i.e. Pressure Limit and Pressure Support Set
- The RR, Ti are directly the result of the patients effort
- Vt is based on the patient effort and the level of support set
Besides CSV what are other less common ways of providing a spontaneous supported breath
PAV, tube compensation or CSV (VS)
Paitent Triggering
For patient triggering the operator must set a sensitivity
Maximum sensitivity means it is the easiest to trigger a breath
Both spontaneous supported breaths and assisted breaths are patient triggered
Pressure Triggering
The patient’s inspiratory effort will causes a drop in pressure in the circuit, and when this pressure drop created exceeds the sensitivity setting a breath is initiated
Eg. Sensitivity set at 2.0 cmH2O – the patient must create a drop in pressure of less than or equal to 2 cmH2O below baseline
In newer vents this sensitivity is below baseline (ie. Below the PEEP level)
In older vents this could be an absolute setting (doesn’t take PEEP into account)
Flow Triggering
The vent measure flow through a measurement of the flow leaving the inspiratory and flow entering the expiratory limb
Normally you will have a continuous flow throughout the circuit
When the patient makes and inspiratory effort the flow returning to the expiratory limb will decrease and this can trigger a breath
Flow triggers is considered to be more sensitive than pressure triggering meaning that there is less work of breathing needed by the patient
Limit Definition
- A limit variable is a parameter that can be reached and maintained at a present level before inspiration ends
- Does not terminate inspiration
- The limit variable can be pressure, volume, flow
Pressure Limit
- There are two ways in which pressure can limit inspiration
-
Pressure is the control variable
- PCV, PS
-
When flow is the control variable
- Commonly used in infants
- Inspiratory flow results in a rise in pressure, the vent will allow this flow until a limit has been reach, then additional flow is vented out of the circuit through a pressure relief valve in order to maintain/limit the pressure that has been set
-
Pressure is the control variable
Volume Limit
The most common volume-limited situation is during an inspiratory pause on a volume controlled breath
The volume is limits throughout the pause
The breath dose not cycle until the pause is up
Flow Limit
Flow is the limit whenever the ventilator is in a flow controlled mode (ex. Volume control)
This means that the present flow has a maximum valve that can be reached during a breath
Cycle Definition
The inspiratory phase will always ends when some variable reaches a present value
This variable is called the cycle and can be: Pressure, Volume, Time, Flow
For each mode there is a primary cycle variable, this is what will normally causes a breath to cycle. However other variables can cause a breath to back-up-cycle (pressure, volume, flow, or time)
Eg. When you set a high-pressure alarm, the breath will cycle when it reaches this press
VOLUME CYCLE
The ventilator ends inspiration after a predetermined volume has been delivered
Volume cycling occurs in a volume controlled setting (when there is no inspiratory pause set)
i.e. When the set Vt has been delivered the breath will end
Volume can also act as a back up cycling mechanism-VTi Alarm
PRESSURE CYCLE
The ventilator will end inspiration after a predetermined pressure has been reached
The gas is delivered during inspiration under pressure, and when the set pressure has been reached the ventilator cycles out of inspiration
This is not a common primary cycling mechanism nowadays, but is always available as a back up cycling mechanism
Time Cycle
The ventilator will end inspiration after a predetermined time has been reached
The vent delivers gas to the patient until the set time interval is over
Time-cycling is the primary cycling mechanism used in PCV and PRVC (and many other modes)
Time is often a back-up cycling mechanism in PSV
Flow Cycle
The ventilator will end inspiration after a predetermined flow has been reached
The positive pressure is provided to the patient until flow drops off to a pre-established level
Inspiration ends when this low “terminal” flow is reached
This is the primary cycling mechanism for PSV
A flow-cycled breath is considered to be patient cycled!
Baseline Definition
The baseline variable is the parameter controlled during expiration
Pressure is the most common parameter controlled
Volume or flow could also be baseline variables but this is never seen
Baseline pressures are always relative to atmospheric (as are all other ventilatory pressures)
PEEP
PEEP= Positive End Expiratory Pressure
This is the application of positive pressure through expiration
By keeping the airway above atmospheric throughout the breathing cycle PEEP maintains the patient FRC and can help to improve residual capacity
PEEP is referred to as CPAP when only using spontaneous breathing
CONDITIONAL VARIABLES
A ventilator can use pressure, volume or time (and their derivatives) as conditional variables
Conditional variables work on the “if-then” principle:
If the value of a conditional variable reaches some preset level, then some action occurs to change the ventilatory pattern
These require closed-loop modes
ALARMS
Alarms can be audible, visible, provide messages, or do a combination of these
Certain alarms can affect breath delivery: High-pressure alarm in volume control ventilation will cycle the breath (ie. This alarm is a back-up cycle). This means that the breath has ended early
Other alarms just function to alert the operator that a parameter is out of the set range
Most alarms can be silenced by the operator while they work to correct the situation
Some critical alarms cannot be silenced: Loss of power (pneumatic or electrical) and Vent inoperative
High Pressure Alarm
30 or 40
High RR Alarm
35
For the evita to set the high RR alarm you need to subtract you set RR from 35 and then that will be your high RR alarm
CMV-VC Pt Applications
Full ventilatory support
Acute control of patient ventilation (MV assured)
Lung protective strategies (ARDS)
Lung protective strategies (ARDS)
We use a lower tidal volume for patients with ARDS
Normal tidal volume is 6-8 mg per kg of ideal body whereas with ARDS you can allow even 4 (permissive hypercapnia- to protect lungs)
VC-IMV OR PC-IMV Pt Applications
Comfort with assured ventilation
Patient capable of some WOB
VC-CSV OR PC-CSV Pt Applications
Comfort, physiological advantages
Patient has intact ventilatory drive
Patient is capable of some WOB
Considered to be a weaning model
Mandatory versus mechanical breaths
Mandatory is a type of mechanical breath
Supportive versus assitsed breaths
Assisted Breath-Type of mechanical breath
Supportive Breath-Type of spontaneous breath
Modes that allow for mechanical breaths
Types of Volume Control
Controlled, CMV-VC, IMV-VC, and CSV-VC
Any Mode that allows for mechanical breaths
Volume Control
A mechanical breath that delivers a set Vt at a set flow rate or alternatively can set a Vt and a Ti (and a flow)
Volume/Flow is the control variable-The volume and flow waveforms remain constant breath-to-breath while the pressure (and P waveform) will vary due to changes in the patients compliance and resistance
As patient compliance will increases the tidal volume will still remain the same as it is set on the machine
As resistance increase the tidal volume remains the same but the pressure needed to deliver the tidal volume will have to increase
What is the initally mode that is used clinically
Now PRVC is often the initial mode used clinically instead of CMV (VC)
RR and Respirtory Drive
If patient has there own respiratory drive it would only matter if you set a respiratory rate higher than what they are breathing if you set it lower nothing will be done to the patient
Volume Control Advantages
Guarantee a low minute volume
You set the minimum RR and Vt
Low WOB with CMV(VC) as long as sensitivity and flow are set appropriately
Remember both mandatory and assisted breaths are allowed in CMV, if the patient wants more breaths the only work they have to do is to trigger the vent, the vent then controls the rest of inspiration
This can also be a disadvantage as the respiratory muscle can atrophy very quickly
Volume Control Disadvantages
Pressures change in response to changes in the patient’s lung mechanics (i.e. Raw and CS)
Flow is fixed (remember we are controlling this!) and may not meet changing demands of the patient
May result in regional alveolar over-distension
Alkalosis is also possible
Air will follow the path of least resistance, meaning that it is possible for one part of the lung will become over inflated- Pressure control is one way to help get equal airflow throughout the lung because there will be an equalized pressure throughout the lungs
Settings-Rate
Will be set as 13
Will determine Total Cycle Time (TCT) which is equal to 60/RR
Settings-Tidal Volume
Tidal Volume=8 x IBW
Setting-Flow
The shape of the flow waveform chosen
Often a square or decelerating flow waveform is used
Settings-Tipause
Something you can set or observe
Alternatively some vents will set VT, flow and TItotal. TIdyn is still determined by the VT and the flow, but now the TIpause is equal to the TItotal – TIdyn.
Settings-Sensitivty
What happen when sensitivity is too high-Take more effort for the patient
If it is too low-Too easy for the patient and might hyperventilate the patient (any leak in system machine thinks that they are trying to breath and then sill start a breath for their patient which is know as auto cycling)
Set at 2?
Tidyn
Will be determined by Tidal volume and flow
Tidyn=Vt (L)/Flow (L/sec)
Settings-TiTotal
TiTotal=Tidyn+Tipause
Settings-TE
Will be determined through Titotal and TCT
TE=TCT-Titotal
TiTotal=Tidyn+Tipause
Compliance Equation
C= Vt (mL) / (Pplat-PEEP) [cmH2O]
Resistance Equation
R (cmH2O/L/sec) = (PIP- Pplat) [cmH2O] / Flow [L/sec]
Minute Ventilation Equation
MV = Rate [breath/min] * Vt [mL)
TCT Equation
TCT [sec/breath] = 60/Rate [breath per minute]
I:E Equation
I:E = Ti/Ti : Te/Ti
Answer should be given has whole numbers ex: 1:4.5
Question if FiO2 is Required
FiO2 required = (PaO2 Desired * FiO2 Present) / PaO2 initial ABG
New PaCO2 Desired
New PaCO2 Desired = Present PaCO2 – [ (pH Goal – pH Present) / 0.01}
New Minute Ventilation Required
MV required = (PaCO2 Initial * MV) / PaCO2 desired
Settings-PEEP
Set at 5?
Maximum Pressure Limit
Max pressure that a ventilator can increase too and is often tied in with the high pressure alarm
lEg. If the High Pressure Alarm is set to 35 cmH2O, the maximum pressure limit delivered on a PRVC breath would be 5 cmH2O below this, and if the vent cannot deliver the target volume within this pressure limit then there will be an alert alarm
lThe ventilator will only adjust the delivered pressures in small increments
lEg. 3 cmH2O per breath
A Pressure Support Breath and transairway pressure gradient
By adding the PS we increase mouth pressure during inspiration and therefore increase the pressure gradient responsible for flow. Thus, more flow into the patient and a larger VT—all for the same spontaneous effort.
As PS levels become high (eg>20) it is approaching FVS-pt has to make a minimal effort to achieve a VT.
Transthoracic Pressure
The transthoracic pressure gradient is the difference between the pressure in the pleural space and the pressure at the body surface, and represents the total pressure required to expand or contract the lungs and chest wall.
Transpulmonary Pressure
The transpulmonary pressure gradient is the difference between the pressure in the alveoli and the pleural space, and is responsible for maintaining alveolar inflation.
Transrespiratory Pressure
The transrespiratory pressure gradient is the difference between the atmosphere (Pm) and the alveoli, and is responsible for the actual flow of gas into and out of the alveoli during breathing.
Pressure Support
Spontaneous supported breath
Can occur in a purely spontaneous mode (CSV-PS) or added to the spontaneous breaths allowed in another mode [eg. SIMV(VC)+PS]
The operator sets the inspiratory pressure (PS level), PEEP, FIO2, and sensitivity
The patient determines the RR, TI, and inspiratory flow
The VT is determined is determined by the PS set, the lung characteristics (R and C) and patient effort
This mode looks very similar to PC but is dramatically different, as pressure at the mouth is only supplied during a patients’ spontaneous inspiratory efforts (flow cycled)
Pmouth is positive but Palv is negative during inspiration
Thus WOB is reduced but more physiologically similar to spontaneous breathing.
PC-CSV-PS
Usually called PSV (Pressure Support Ventilation)
One of the most used modes of ventilation
When is PC-CSV-PS Uses
Used for spontaneously breathing patients (they must still have their drive to breath) who:
Require partial ventilatory support (PVS) not FVS- i.e. The patient is spontaneously breathing but requires some support to ¯ WOB
Are being weaned from the ventilator
May have a small VT or high RR
Advantages of Pressure Support
Patient sets own rate, TI, inspiratory flow and VT (very comfortable mode)
Augments the patient’s tidal volume
Increase the VT (with same pt effort)
Can be used in conjunction with other modes that allow spontaneous breaths (to ¯ WOB of S breath)
Maintains and builds respiratory muscle function (can be used for weaning)
Disadvantages of Pressure Support Mode
Not to be used on patients with an inconsistent, irregular or unreliable ventilatory drive
Need to protect the patient with alarms-especially an apnea alarm
Pressure Support Phase Variables
Trigger: Patient only
Limit: Pressure
Cycle: Inspiratory Flow (Back-up time-cycle in case of leaks)
Pressure Support Settings
PS level
PEEP
FIO2
Sensitivity-B/c there is pt. triggering, depending on the vent used this may be pressure-triggering, flow-triggering or volume-triggering
Pressure Support Versus Pressure Control Waveforms
