Auto Flow 20Questions – 20Answers - FRCA - … Booklet.pdf · 20Questions – 20Answers using...

Auto Flow®

20 Questions – 20 Answers

Joseph Fitzgerald

Important Notice:

Medical knowledge changesconstantly as a result of newresearch and clinical experience.The author of this introductoryguide has made every effort toensure that the information given is completely up to date,particularly as regards applicationsand mode of operation. However,responsibility for all clinicalmeasures must remain with thereader.

Written by:

Dräger Medizintechnik GmbHJoseph FitzgeraldMoislinger Allee 53/5523542 LübeckGermany

All rights, in particular those ofduplication and distribution, are reserved by Dräger Medizin-technik GmbH. No part of this work may be reproduced or storedin any form using mechanical,electronic or photographic means,without the written permission ofDräger Medizintechnik GmbH.

ISBN 3-926762-40-3

Auto Flow®

20 Questions – 20 Answers

Joseph Fitzgerald

20 Questions – 20 Answers using AutoFlow®4

Contents

■ What is AutoFlow®? 6

■ Is AutoFlow® a new Ventilator Mode? 7

■ When would you use AutoFlow®? 8

■ How does AutoFlow® compare to BIPAP 9

■ How is AutoFlow® combined with other modes such as IPPV? 10

■ How does AutoFlow® work with SIMV? 11

■ How does AutoFlow® work with MMV? 12

■ How does ventilation with AutoFlow® compare with volume controlled ventilation? 14

■ How does ventilation with AutoFlow® compare to pressure regulated modes? 15

■ What type of lung diseases is AutoFlow®

suitable for? 16

■ Are there situations where it is not indicated? 17

■ What has to be considered when switching fromconventional modes to AutoFlow®? 18

■ How do you set up AutoFlow®? 19

■ What monitoring parameters are important toobserve when using AutoFlow®? 20

20 Questions – 20 Answers using AutoFlow® 5

■ What are the advantages to observe when using AutoFlow®? 22

■ What would be the subsequent management of the patient? 23

■ What are the safeguards againsthypo/hyperinflation? 24

■ How does AutoFlow® interact with inverse ratioventilation? 25

■ How can mechanical ventilation and spontaneous breathing be mixed in one mode? 26

■ What is the technology behind this latest advance in therapy? 28

Explanatory note: In some regions of the world IPPVmode of ventilation is referred to as CMV andAssist/CMV. The mode BIPAP is referred to as PCV+ inthe USA and Canada. BIPAP* is trademark used underlicence. AutoFlow® is registered as a trademark ofDräger Medizintechnik GmbH.


1. What is AutoFlow®?

This is a new advance in volume controlled modes of mechanical ventilation where the ventilatorautomatically regulates inspiratory flow. This autoregulation is in accordance with the set VT andcurrent lung compliance.

The set VT is always given at minimum possiblepressure and spontaneous breathing is possible (openvalves) through the whole Inspiratory and Expiratoryphases of the mechanical ventilatory cycle.

A decelerating flow pattern reduces Peak pressuresand as lung compliance changes further they arerecognised and responded to.

Flow

V

Volume Controlled Switch-on AutoFlow®

T VT

A decelerating flow patternreduces Peak pressures


2. Is AutoFlow®

a new Ventilator Mode?

It is a new addition to all volume controlled modes onthe Evita 4 and Evita 2 dura ventilator. It is not a modeindependently selected in itself. It could be comparedto the way one function enhances another such asflow trigger enhances pressure support.

It is intended to simplify strategies in mechanicalvolume controlled ventilation by offering more patientbenefits with a wider therapy range and with lessparameters to adjust.


3. When would you use AutoFlow®?

There are very few exceptions to using AutoFlow® inall volume oriented modes where it is available. Ingeneral we can divide its use into two areas, that ofthe type of ventilatory strategy we want to apply andthat of the type of patient that it is particularly suitedto. In the first case in volume strategy ventilationwhere we want to reduce high airway pressures andcapitalise on spontaneous breathing with reduced useof sedation and muscle relaxants. The deceleratingflow and the regulated inspiratory and expiratoryvalves provide a response to every inhalatory andexhalatory effort of the patient. This feels like breathingthrough an open system.

In other strategies we may want to use inverse ratiotimings. The occlusion of the expiratory valve for suchlengths of time can produce risk of barotrauma for apatient who becomes awake and starts breathing.With an open breathing system this risk is greatlyreduced.

In terms of patient types, there are those with quitevariable compliance levels after surgery who requirecareful manipulation of inspiratory pressure andvolume to prevent barotrauma and hyperinflation.AutoFlow® continually adjusts the pressures ascompliance changes to ensure volume delivery at thelowest possible pressures.

Finally, as a smooth weaning strategy we want thefirst efforts by the patient to be responded to in allphases of the mandatory stroke unlike conventionalmodes of SIMV where there are closed phases in thecycle. The fixed set VT delivery of SIMV is also addressedfor Bronchospasm patients with air hunger as alldemands for flow and volume are responded to by theventilator.


4. How does AutoFlow®

compare to BIPAP?

BIPAP has been established for a number of years as a real advance in pressure controlled ventilationstrategies. Pressures are regulated at a specific valueand pressure peaks are eliminated and together withtime synchronisation the patient is able to breathespontaneously at any stage. Many of these features arenow transferred across into the volume controlledmodes as the benefits of this therapy have becomemore extensively accepted. The prime parametersetting in BIPAP is inspiratory pressure (Pinsp) andtidal volume (VT) is variable, the prime adjustment inAutoFlow® is VT and the pressure is the variable,depending on the compliance.

Many benefits of BIPAP are transferred into volumecontrolled modes withAutoFlow®


5. How is AutoFlow®

combined with other modessuch as IPPV?

The addition of AutoFlow® to IPPV mode for example is achieved by the on-going measurement of pressure,flow, volume and lung compliance and a ventilatorresponse that regulates the flow to achieve the set VTin the inspiratory time available. When you switch onthere is a change from manual control to an automaticcontrol of the inspiratory flow. Other than the removalof the control knobs of pressure (Pmax) and flow fromthe touch screen panel all the core settings includingtrigger function and pressure support capability aretotally unaffected.

The core settings includingtrigger function and pressuresupport are unaffected.



work with SIMV?

Equally in SIMV any of the usual parameters such as PEEP are fully functional and superimposingAutoFlow brings auto-regulation to the flow andpressure.

The associated potential advantages have a dominoeffect in that a lower peak pressure usually means alower mean airway pressure with a positive effect onhaemodynamics, the inspiratory flow varies accordingto individual patient needs and may alter on a breathto breath basis. AutoFlow® supports the preservation ofan intact respiratory drive as less sedation and musclerelaxants are used. The matching of flow and volumeto patient needs in synchrony with inspiratory time at minimum pressure promotes harmony betweenpatient and ventilator. This reduces considerably thephenomena known as “fighting the ventilator” whichis a misnomer in that the “ventilator fights the patient”with its imposed fixed settings.

AutoFlow® supports thepreservation of an intactrespiratory drive as less sedation and musclerelaxants are used.



work with MMV?

The mode is similar to SIMV in many respects wherethe clinician sets a rate and VT for the patient to satisfyadequate gaseous exchange. It differs from SIMV inthat as spontaneous breathing activity increases andthe patient achieves more than the set mandatoryminute volume then the mechanical strokes fade intothe background. The patient, often with the aid ofpressure support takes over the full volume work ofminute ventilation. In MMV, AutoFlow influences themechanical strokes if present and reduces asynchronyby allowing spontaneous breathing activity andreducing pressures to a minimum.

The logical progression of this is that the patientcan be sedated and on full controlled ventilation, ashe wakes up he will still get mechanical strokes but he will be able to breathe through them and notexperience any discomfort with these breaths ,as hiscontribution increases the ventilator breaths fadeaway completely so the patient does not have to beswitched to a weaning mode.

In addition to this if we now use the Ideal BodyWeight setting and programme the weight into theventilator before start of therapy then the right volumeand ventilator settings will be selected for that patientand appropriate alarm defaults also. All this meansthat post operatively we can easily select what we wantfor the patient and in straight forward ventilationcases we can start with full ventilation therapy and goright through to full spontaneous breathing withouthaving to readjust the ventilator.

No ventilator adjustmentrequired when going fromfully controlled ventilation tofull spontaneous breathing.


■ Select Ideal Body Weight (70 kg).Key values and alarms set automatically

■ Set ventilator to standby function.

■ Connect arriving patient. Start ventilation

■ Record monitored parameters

■ Maintain observation of the patient as they wake up.

MMV AutoFlow

ControlledVentilation

Spont. effortsand

mandatory phases

Total spontaneousefforts

CPAP withpressure support

Ideal body weight 70 kg


8. How does ventilation withAutoFlow® compare withvolume controlled ventilation?

The constant flow in Volume controlled modes doesnot always match inspiration times, flow and volumedo not always match patient demand leading to asyn-chrony. Peak pressures are often high sedation andparalysis are used to adapt patient to the ventilator.Spontaneous breathing if allowed is a futile struggleagainst closed valves. Attempts to exhale during

mandatory phase activatehigh airway pressurealarms. The freedom forthe patient to coughfreely and clear his ownsecretions during volumecontrolled modes isusually suppressed. In any situation AutoFlow®

always provides safety and lower pressurescompared to normalvolume controlled modes.

controlled patient activity

Flow

Paw

t

texpiration

closed

in

ex

inspirationclosed

fixedflow


9. How does ventilation withAutoFlow® compare topressure regulated modes?

AutoFlow® decelerates flow automatically similar topressure controlled ventilation. Inspiratory pressurefollows compliance similar to plateau pressure involume controlled ventilation.

It differs from conventional pressure limited modesand Pressure Regulated Volume modes in allowingspontaneous breathing at any phase. It guarantees aset VT and keeps pressure to a minimum whereaspressure controlled modes keep pressure constant andallow the VT to vary. AutoFlow® brings many of thefeatures of PCV to volume oriented modes and allowsthe benefits experienced by BIPAP users for example tobe shared with those who wish to pursue volume onlystrategies.


Flow

Paw

t

texpiration

closed

in

ex


10. What type of lung diseases is AutoFlow® suitable for?

The use of AutoFlow® is indicated as part of a volumeoriented strategy in all cases where you can expectquick changes and short term improvement of lungcompliance.

It is recommended in post surgical cases whereacute restriction is evident and you want to guaranteenormal ventilation. In acute lung oedema where highairway pressures are initially acceptable but as thetreatment programme takes effect pressures will godown automatically and volumes will stay constant.Using AutoFlow® with a volume controlled mode iseasier to handle than pressure control in this situation.

In cases where local atelectasis resulting fromtrauma or pneumonia requires frequent repositioningof the patient, in these situations Pressure Controlwould produce great volume changes and AutoFlow®

in volume control modes will provide stable volumesat minimum pressures.

Finally, AutoFlow® is suitable for all start upventilation therapy scenarios where there is limitedinformation on disease status available and it isimportant to get therapy underway where pressuresand flow are regulated and spontaneous activity is not compromised.


11. Are there situations where it is not indicated?

The range of uses of AutoFlow® is determined by thelimitations of volume controlled modes and thesemodes are not always recommended for very severediseases with long term healing processes with severaldays to weeks required to improve lung conditions.These cases where Acute Lung Injury and ARDS areclearly established often require a defined pressurecontrol strategy such as BIPAP or APRV mode wherethe small volumes associated with the reopening lungare essential for blood gas improvement. Currentopinion among the experts advocate reducing the riskof barotrauma by regulation of pressure and minimalvolume strategy.

Volume controlled ventilation may not be indicatedwhere there is a risk of intrinsic PEEP and the associ-ated danger of over inflating the lung in a volumecontrolled strategy, especially where there are obstruc-tive disorders or long (inverse) ratios are required. Inthese cases BIPAP mode with respect to deceleratingflow and spontaneous breathing activity has the sameadvantages as AutoFlow®.

Lung disease is the realindicator and pressure orvolume strategy is selectedaccordingly.


12. What has to be consideredwhen switching fromconventional modes toAutoFlow®?

The important point is that settings stay the same andif there is no patient activity there will be no variancein VT. PEEP and Tinsp and mandatory frequencyremain stable. Setting the flow control is not necessaryas there is automatic regulation. As in all volumecontrol modes setting the upper Paw alarm is importantfor the upper pressure threshold. Ventilation relatedsedation can be reduced to avail of the full benefits ofspontaneous breathing.

Pinsp

Pressure

Volume Controlled Switch-on AutoFlow® Compliance improvement


13. How do you set up AutoFlow®?

AutoFlow® is switched on through “extra settings” ontouch screen and rotary confirm knob. Conventionalparameters – Freq, Tinsp, VT and PEEP are set asdesired. Upper Paw alarm should be set to warn ofsudden compliance decrease or resistance increaseand subsequent pressure changes. Upper Insp VTalarm can be set to indicate increasing spontaneousbreathing VT demands.

Set up operation is byfollowing screen prompts.


14. What monitoring parametersare important to observewhen using AutoFlow®?

On switch on Peak pressure decreases as flowdecelerates

Pinsp will adjust as compliance alters. Mean press-ures will follow. The inspiratory flow pattern will alter(may lengthen) to accommodate resistance changes.Airway pressure high alarm unlike conventionalventilation will not occur (but should always be set).In case the VT is not applied because of high resistancea VT low alarm is automatically generated.

Spontaneous breathing activity will appear on flowcurve. No high Paw alarm will activate on activeexpiration and mean VT equals set VT. Pressure, VTand SB rates are monitored and displayed in anyformat which is preconfigured. Observance of the PV loops on the screen will show much improvedpressure to volume relationships. Trends for many ofthese parameters provide a good indicator of clinicalprogress.

In case the VT is not applied aVT low alarm is automaticallygenerated.


Paw

Pinsp. = f (V T,C)

PEEP t

TI

1

Paw

TE

Flow

t

f

without spontaneous breathing with spontaneous breathing

VT

Peak pressuredecreases with decel-erating flow

■

■ Pinsp adjusts to compliance

Spontaneousbreathing activity seen on flow curve

■

No high Pawalarm onspontaneousbreathing

■

Trends give best overview

■


15. What are the advantages toobserve when using AutoFlow®?

Peak and Mean airway pressures are reduced. Lessinvasive, less mechanical controlling by the ventilator.In the presence of leaks AutoFlow® recognises andcompensates accordingly. Less requirement forsedation and muscle relaxants which have many othersystemic effects. Spontaneous breathing contributes tobetter gas exchange and secretion clearance. Weaningis more smooth and can start earlier. Greater comfortand less stress for patients should in turn reducestress levels for clinical staff.

Finally, the need for fewer control knobs to adjustand less alarms to manage are seen as real advantagein the busy intensive care unit.


16. What would be the subsequentmanagement of the patient?

Each case is different but a general strategy duringweaning would be to reduce FiO2, maintain PEEPabove lower inflection point, reduce Tinsp to I:E of 1:1and reduce Frequency.

As patient activity increases and patient inhaleswith the mandatory stroke inspiratory pressures willautomatically reduce and the next step is PressureSupport to assist the spontaneous breathing.

The significant point of management is the earlymove to spontaneous breathing because of the opensystem which allows an early parallel reduction inmechanical ventilation. The use of CPAP combinedwith Pressure Support to compensate for the work ofbreathing through the tube is usually indicated as thefinal therapy stage.

The tranisition to finalweaning steps is simple andstraightforward.


17. What are the safeguardsagainst hypo/hyperventilation?

The safeguards against too much or too little volumecome in three forms. Firstly the user is preventedfrom making unusual inadvertent settings by use of onscreen advice and having to confirm before being ableto implement these settings. Secondly the increasingincremental steps as compliance changes are just3 mbar and are limited to 5 mbar below the set upperairway pressure alarm. Thirdly, the automaticallyactivated Volume inconstant alarm warns if the set VT is not applied due to compliance or resistancechanges. The upper airway pressure alarm warns ofextreme coughing or obstruction. The VTi alarm limitsthe inspiratory volume in the event of too great avolume demanded.

Frequent triggering by the patient does not lead tohyperventilation in the modes SIMV and MMV andwhere it might have been possible in CMV/Assist thetrigger can be turned off but the patient is stillallowed to breathe spontaneously.


18. How does AutoFlow® interactwith inverse ratio ventilation?

AutoFlow® is an excellent adjunct to long inspiratorytime settings. Clinical experience is limited but if wecarry across the reported experiences of Sydow et al(2)and apply a ventilatory strategy where spontaneousbreathing is encouraged with the longer inspiratorytimes but overall pressures are low then this shouldprovide a good indication for its use in an IRV format.Not withstanding the impact of air trapping thisshould actively contribute to reducing the risk ofbarotrauma which is often associated with IRV.

Pre

ssur

eFl

ow

end-expiratoryalveolar pressure

AutoFlow® is ideally suited toextended inspiratory times.


19. How can mechanical venti-lation and spontaneousbreathing be mixed in onemode?

To facilitate spontaneous inspiration and expiration ineach phase of controlled mechanical ventilation is atechnological challenge. This unique solution is basedon an intelligent microprocessor system combinedwith highly sophisticated valves, flow and pressuresensors.

Conventional technology with the delivery of fixedflow and volume in each mandatory breath is contraryto free spontaneous breathing by the patient. Volumecontrol with AutoFlow® is therefore provided on abreath to breath basis. In each individual breath the patient has the possibility to increase or reducethe delivered volume. The ventilator monitors theinspiratory volume and compensates for deviations in the next breath.

In case the volume was too low, volume of the nextbreath will be automatically adjusted by increasedinspiratory pressure (Plateau). If the volume was too high either because of spontaneous inspiration or improving compliance, inspiratory pressure willautomatically go down with the next breath. Forsmooth interaction with the patient the pressurechanges are limited to maximum of 3 cm H2O frombreath to breath. Great pressure fluctuations becauseof unique events like a cough or a spontaneous sighare thus avoided.

New microprocessor systemscombined with sophisticatedvalves provide new solutions.


AutoFlow® responds like a CPAP system with CPAPvalue set to Pinsp. Whenever the patient tries to inhalemore volume the demand valve will deliver more flow,whenever he wants to exhale the expiration valve willallow expiratory flow while the pressure/PEEP level iskept constant. The graphs above illustrate this.

The patient can inhale and exhale as usual in SIMV/MMV and now even in the expiratory phase of IPPV.


Patient

Flow

Paw

t

in

ex

t

texpirationopen

inspirationopen

in

ex


20. What is the technologybehind this latest advance in therapy?

All the electronic and pneumatic subsystems need tobe optimised for a function like AutoFlow®.

The accurate control of flows and pressures is anessential basic requirement, but only intelligentalgorithms and fast adjustments of the valves can pro-vide the required responsiveness to patient activities.

Evita ventilators havehighly responsive inspira-tory demand valves thatcan open and close inmilliseconds on commandof the microprocessorsystem, while keeping the FiO2 and pressureconstant. This minimisespatient work of breathingand helps avoid inefficientbreathing efforts.

The integrated specialexhalation valve design

with a large control orifice provides low resistance toexhalation. Pressure is controlled smoothly with fastresponses throughout the whole setting range of PEEPand inspiratory pressures. As the picture here on theleft illustrates, the exhalation valve is never occludedcompletely, the closing pressure is always equal to thecorresponding PEEP or inspiratory pressure. Like apop off valve it permits expiratory flow if the pressureexceeds the set value.

Last but not least accurate and robust pressure andflow sensing systems on both in- and expiratory sideare a basis for all these functions.

ExpirationvalveclosedorExpirationvalvecontrolled


Summary Statement of Benefits of Auto Flow®

Physiologic facilitates the recognisedimportance of spontaneousbreathing in controlledventilation

Synchrony flow and volume adapted topatient needs

Automatic complete weaning therapy inmany situations when MMV iscombined with Ideal BodyWeight and one pre-setting.

Simplification ventilatory therapy with lesscontrol knobs and less alarms

Evidence All proven benefits of BIPAPnow transferred to volumecontrolled ventilation

Volume controlled ventilationtakes a major step forward.

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Dräger Medical AG & Co. KGaA

23542 LübeckMoislinger Allee 53-55

GERMANYPhone: +49-1805-3 72 34 37Fax: +49-451-882-37 79E-mail: [email protected]

Europe, Middle East, Africa:

Latin America / Iberian Peninsula:

Dräger Medical Hispania S.A.c/ Xaudaró n° 528034 MadridSPAINPhone: +34-91-728 34 09Fax: +34-91-358 51 61E-mail: [email protected]

Asia / Pacific:

Draeger Medical Asia Pacific Ltd.Unit 2205, 22nd floorHarbour Centre25 Harbour RoadWanchaiHONG KONGPhone: +852-28 77 30 28Fax: +852-28 77 33 37E-mail: [email protected]

www.draeger-medical.com

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