Classification of Ventilators Flashcards Preview

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Flashcards in Classification of Ventilators Deck (120):

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



Modes You Can Be In



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




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

  1. Mandatory: Ventilator initiated
  2. 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



Delivered both mandatory and assistented mechanical breaths

Also called Assist/Controlled (A/C)



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)



Mechanism used by vent to initiate the start of inspiration


Possible Triggers

  1. Manual- Button on vent that allows operator to manually trigger a breath
  2. Time
  3. 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



Trigger-Patient or time






Trigger-Time or Pt.






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 



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




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 




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= 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



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 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


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 



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



The shape of the flow waveform chosen

Often a square or decelerating flow waveform is used




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.



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?



Will be determined by Tidal volume and flow

Tidyn=Vt (L)/Flow (L/sec)









Will be determined through Titotal and TCT




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



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.



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



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