oxylog_3000_plus_autoflow_guide_dec_2009.pdf
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D-9125-2009
AutoFlow®
The Oxylog 3000 plus incorporates the benefits of pressure
controlled ventilation into volume controlled ventilation
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Foreword
Dear reader,
Performing mechanical ventilation during emergency care is a real challenge.
Especially in out-of-hospital situations there are many problems to solve in a
minimum of time. In addition, environmental factors play an important role
in the performance that can be achieved.
In emergency situations, patients often have spontaneous respiratory efforts.
However, when mechanical ventilation is needed in the field, many health
care providers prefer volume controlled ventilation modes. Deep sedation is
needed to let the patient accept this kind of ventilation, often complicated by
negative effects on circulation and resulting in possible secondary brain
injury or increased stress to the heart.
With AutoFlow® spontaneous ventilation efforts of the patient are accepted
in volume controlled modes, resulting in less stress, reduced need for deep
sedation and better pressure control. The emergency care provider’s ability to
stay in control of the whole situation is improved.
This booklet provides an overview of the different aspects of AutoFlow and
focuses on emergency care and transport ventilation with the Oxylog 3000
plus. It aims to answer the main questions that you might have and describes
the areas where AutoFlow could contribute to the ventilation therapy applied
in this field.
We hope this booklet provides information which helps you provide safety and
comfort for your ventilated patients!
Prof. Frans L. Rutten, MD
Best, the Netherlands
December 2009
Thomas Peyn
Lübeck, Germany
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AUTOFLOW IN EMERGENCY CARE & TRANSPORT VENTILATION
Editor
Dräger Medical GmbH
Moislinger Allee 53–55
D-23542 Lübeck
www.draeger.com
Authors
Prof. Frans L. Rutten, MD
Application & Training Specialist
Clinical Consultant
Dräger Medical b.v.
Kanaaldijk 29
NL-5683 CR Best,
The Netherlands
Application & Training Specialist:
Thomas Peyn
Dräger Medical GmbH
Moislinger Allee 53-55
D - 23542 Lübeck
Germany
Important notes
Medical knowledge is subject to constant change due to research
and clinical experience. The authors of this publication
have taken utmost care to ensure that all information
provided, in particular concerning applications and effects, is
current at the time of publication. This does not, however,
absolve readers of the obligation to take clinical measures
based on their own medical knowledge and judgment.
The use of registered names, trademarks, etc. in this publication
does not imply, even in the absence of a specific
statement, that such names are exempt from the relevant
protective laws and regulations.
Dräger Medical GmbH reserves all rights, especially
the right of reproduction and distribution. No part of this
publication may be reproduced or stored in any form by mechanical,
electronic or photographic means without the prior
written permission of Dräger Medical GmbH
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CONTENTS
1.
2.
3.
4.
What is AutoFlow?
How is AutoFlow set up?
What happens when AutoFlow is activated?
How are spontaneous efforts mixed with mandatory volume
controlled strokes?
5. How does AutoFlow compare to PC-BIPAP/PC-SIMV+*?
6. How does AutoFlow work with VC-CMV and VC?
7. How does AutoFlow work with VC-SIMV?
8. What advantages are observed when using AutoFlow?
9. How do leaks (e.g. in NIV) affect AutoFlow?
10. When can AutoFlow be used?
11. What monitoring parameters are important to observe
when using AutoFlow?
12. What safeguards are there against hypo/hyperventilation?
13. What is the value of AutoFlow in patients with head injury or stroke?
14. What is the value of AutoFlow after return of spontaneous circulation
(ROSC)?
15. What is the value of AutoFlow in blunt thoracic trauma?
16. What is the value of AutoFlow in patients who are ventilated via a
supraglottic airway?
Abbreviations
Summary
Explanatory notes:
In some regions of the world VC-CMV mode of ventilation is referred to as IPPV.
IPPV Assist is identical to VC-AC. The mode BIPAP* is referred to as PC-SIMV+
in the USA and Canada.
AutoFlow® is a registered trademark of Dräger Medical GmbH
* trademark used under license
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AUTOFLOW IN EMERGENCY CARE & TRANSPORT VENTILATION
1. What is AutoFlow?
AutoFlow is an adjunct to volume controlled ventilation mode, it automatically regulates inspiratory flow and inspiratory pressure. When AutoFlow
is activated the inspiratory flow pattern changes from the constant flow
typical of volume controlled ventilation to a decelerating flow pattern usually
associated with pressure controlled ventilation.
AutoFlow
– Is available in all volume controlled modes such as VC-CMV, VC-AC,
VC-SIMV, VC-SIMV/PS.
– Delivers the set tidal volume at the lowest possible inspiratory pressure.
– Reduces peak airway pressures.
– Allows the patient to breathe any time in the respiratory cycle.
Flow
Volume Controlled
VT
D-9565-2009
VT
Switch-on AutoFlow®
Fixed flow pattern versus decelerating flow pattern delivering identical tidal volume.
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2. How is AutoFlow set up?
AutoFlow is an adjunct to volume controlled ventilation mode. It is found in
the Oxylog 3000 plus “settings” menu. Once the function has been selected it
is switched on by pressing the rotary knob.
There is no need to change other settings or alarm limits once AutoFlow
is activated as long as they meet clinical needs. The Pmax setting has an
additional function during AutoFlow: it limits the inspiratory pressure
control to a level of 5 mbar below the Pmax setting.
MT-5833-2008
AutoFlow is only available in volume controlled modes.
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AUTOFLOW IN EMERGENCY CARE & TRANSPORT VENTILATION
3. What happens when AutoFlow is activated?
Once AutoFlow is activated the next mandatory ventilation stroke is delivered
with the minimal flow required to deliver the set volume within the set inspiratory time. The resulting end inspiratory pressure is used as the inspiratory
pressure for the next breath.
Subsequently a decelerating inspiratory flow profile is used. Once expiration
begins delivered (inspiratory) volume is compared to the set tidal volume.
The inspiratory pressure of the next mandatory stroke is adjusted, up or
down, according to the measured inspiratory volume of the previous breath.
The inspiratory pressure is adjusted by a maximum of plus or minus 3 mbar
per breath. The inspiratory pressure will not increase to more than 5 mbar
below the upper airway pressure alarm limit. If the set tidal volume can no
longer be achieved, an alarm “VT low, pressure limit” is generated.
Spontaneous breathing may cause fluctuations in the tidal volume, however,
AutoFlow ensures a constant tidal volume is applied, on average, over time.
It is always possible and useful to use AutoFlow provided there are no
specific pulmonary restrictions and the patient is receiving volume controlled
ventilation.
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Pressure
Volume Controlled
Switch-on AutoFlow®
D-9566-2009
Pinsp
Compliance improvement
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AUTOFLOW IN EMERGENCY CARE & TRANSPORT VENTILATION
4. How are spontaneous efforts mixed with
mandatory volume controlled strokes?
Traditionally in volume controlled modes the ventilator closes the expiratory
and opens the inspiratory valve for a defined period of time. After the gas has
been delivered a pause (plateau) may occur and both valves are closed before
the expiratory valve opens to enable expiration. Generally the ventilator does
not respond to spontaneous efforts during such a mandatory stroke. High or
low airway pressure alarms may be seen and are obvious indicators that the
patient is fighting the ventilator.
Volume Control without Autoflow
patient activity
controlled
Paw
t
Flow
fixed
flow
inspiration
closed
in
D-9567-2009
expiration
closed
Patient activity without AutoFlow
ex
t
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Several technical requirements have to be met to improve breathing comfort
and reduce the invasiveness of mechanical ventilation: apart from the need
to have a fast gas delivery system to meet additional flow requirements it is
also necessary for the expiratory valve to respond immediately in case of
pressure rises. This “Room to Breathe” concept was realized in the pressure
controlled PC-BIPAP/PC-SIMV+ mode for the very first time. AutoFlow incorporates the same “Room to Breathe” principles as PC-BIPAP/PC-SIMV+,
enabling spontaneous breathing throughout the respiratory cycle which facilitates stress-free volume controlled ventilation.
Volume Control with Autoflow
patient activity
controlled
Patient
in
ex
t
Paw
t
Flow
inspiration
open
in
ex
D-9568-2009
expiration
open
Patient activity with AutoFlow
t
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AUTOFLOW IN EMERGENCY CARE & TRANSPORT VENTILATION
5. How does AutoFlow compare to
PC-BIPAP*/PC-SIMV+ ?
Volume controlled ventilation with AutoFlow and PC-BIPAP/PC-SIMV+ both
facilitate the “Room to Breathe” concept and allow the patient to breathe
spontaneously at any time in the respiratory cycle.
PC-BIPAP/PC-SIMV+ is a pressure controlled mode and the tidal volume (VT)
provided results from the pressure difference between inspiratory (Pinsp) and
expiratory (PEEP) pressure. Changes in lung compliance during
PC-BIPAP/PC-SIMV+ cause changes in tidal volume.
AutoFlow follows a different strategy: As tidal volume is the primary parameter
in volume controlled ventilation, changes in lung compliance conditions
cause changes in the inspiratory pressure (while the volume remains stable).
This is how AutoFlow supports volume protective strategies.
* trademark used under license.
PC-BIPAP/PC-SIMV+ VC-SIMV/AutoFlow
Pressure & Trigger
D-9569-2009
Time
Volume
PEEP
PEEP
Pinsp
–
Pressure Support
Pressure Support
Trigger
Trigger
RR
RR
Ti or I:E
Ti or I:E
Slope
Slope
–
VT
Key settings in PC-BIPAP/PC-SIMV+ and VC-SIMV / AutoFlow
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6. How does AutoFlow work with VC-CMV and
VC-AC?
VC-CMV is a volume controlled mode and does not respond to patient effort.
With VC-AC the patient can trigger additional mandatory strokes.
AutoFlow does not change the cycling characteristic of any mode and ventilation can be conducted as usual. When the patient starts making spontaneous
breathing efforts AutoFlow increases or decreases the gas flow according to
these efforts. Such an improvement in synchrony can reduce the frequency of
airway pressure alarms and increase breathing comfort dramatically.
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AUTOFLOW IN EMERGENCY CARE & TRANSPORT VENTILATION
7. How does AutoFlow work with VC-SIMV?
VC-SIMV can be used on patients with spontaneous breathing. Settings of
VC-SIMV can be combined with Pressure Support and set mandatory strokes
are synchronized to spontaneous efforts.
AutoFlow automatically regulates inspiratory flow and inspiratory pressure
during the mandatory strokes. AutoFlow can improve breathing comfort,
especially if spontaneous breathing interacts with mandatory strokes.
In such a case AutoFlow provides gas flow according to the patient’s needs
and prevents the patient from being starved of air. AutoFlow does not affect
Pressure Support strokes.
In VC-SIMV/PS the total minute volume results from set volume (RR x VT)
plus spontaneous volumes.
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8. What advantages are observed when using
AutoFlow?
Patients who require ventilation in emergency situations often have
spontaneous breathing efforts. Many healthcare providers prefer to ventilate
patients in a volume controlled mode to ensure that the patient gets the tidal
volume they need, especially in hectic situations where continuous control
of the ventilator is not always possible. AutoFlow allows volume controlled
ventilation to accept spontaneous breathing of the patient.
Deep sedation should be avoided as it may result in serious complications
due to negative hemodynamic effects and reduced clinical (neurologic)
control of the patient. AutoFlow makes it possible to ventilate patients in a
volume controlled mode in situations where deep sedation or muscle
relaxation of the patient to depress spontaneous breathing is not required.
Spontaneous breathing contributes to better gas exchange and secretion
clearance.
Greater comfort and less stress for patients should in turn reduce stress for
medical staff.
Lower airway pressure results in a lower intra-thoracic pressure which has a
positive effect on hemodynamics, as well as lowering intracranial pressure
and reducing the chance of a (tension) pneumothorax.
Finally, the need to adjust fewer controls and reduced alarm management
requirements are seen as beneficiary in hectic emergency care situations.
Summary: AutoFlow® minimizes airway pressures while ensuring a
pre-selected tidal volume delivery providing improved safety
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AUTOFLOW IN EMERGENCY CARE & TRANSPORT VENTILATION
9. How do leaks (e.g. in NIV) affect AutoFlow?
Leaks often occur during mask ventilation and are compensated for by an
additional gas flow from the ventilator. Pressure controlled modes automatically detect the drop in pressure caused by a leak and react to maintain the
set pressure level.
AutoFlow enables non-invasive ventilation (NIV) to be applied in volume
controlled modes and can help to increase patient compliance. When
patients are ventilated with a mask the airway is not protected and gastric
insufflation and subsequent aspiration of gastric contents may occur.
This risk can be reduced when airway pressures are kept below
20 mbar/ cmH20.
When using AutoFlow in volume modes, a sudden increase in resistance
(e.g. airway obstruction) does not result in a sudden rise in airway pressure;
instead the inspiratory pressure is adjusted to a maximum of 3 mbar/cmH20
breath to breath. The maximum inspiratory pressure in AutoFlow is limited
to 5 mbar/cmH20 below Pmax. For example: if Pmax has been set to
25 mbar/cmH20, the maximum inspiratory pressure will not rise above
20 mbar/cmH20.
When AutoFlow is used, changes in inspiratory pressure may be seen
from breath to breath. Reasons for such pressure adaptations can be
lung compliance changes, patient efforts as well as variations in leaks.
If clinical circumstances require stable pressure conditions or leaks vary
widely, pressure controlled modes are a preferred ventilation strategy.
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D-9131-2009
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10. When can AutoFlow be used?
Indications and contra indications of AutoFlow are based on the limitations
of volume controlled modes. Independent from the AutoFlow function
volume controlled ventilation may not be indicated where there is a risk
of intrinsic PEEP and the associated danger of overinflating the lung in
volume controlled strategy. This applies especially if obstructive disorders
are present or long inspiration times and relatively short expiration times
(inverse ratio) are required. In these cases pressure controlled modes like
PC-BIPAP/PC-SIMV+ are preferred because of stable pressure conditions and
an improved intrapulmonary gas distribution. Pure pressure controlled
modes are also favored in patients with uncuffed tubes or in adult patients
with significant and varying leaks.
Volume controlled modes combined with AutoFlow are indicated whenever
the volume applied should remain stable and changes in inspiratory pressure
(as typical for any volume controlled mode) are tolerable. In terms of patient
types there are those with quite variable compliance levels e.g. after open
chest surgery or due to re-positioning. Here a volume controlled mode combined with AutoFlow is easier to handle than pressure controlled ventilation
where careful manipulation of pressure levels is considered necessary to
keep the volume stable and to prevent hyper- or hypoventilation.
Emergency patients tend to have spontaneous breathing efforts, continuously
or during painful or stressful events. This often results in reduced synchrony
with the ventilator causing high or low airway pressures, which in turn can
result in serious side effects such as increased intracranial pressure, reduced
oxygenation, worsening of hemodynamics, etc. AutoFlow combines volume
controlled modes with the possibility of synchronization of the ventilator to
the patient’s breathing efforts, resulting in fewer side effects as mentioned
above.
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Finally, AutoFlow is suitable for all start up ventilation therapy scenarios
where there is limited information on disease status available and it is important to get therapy underway where pressures and flow are regulated and
spontaneous activity is not compromised.
Summary: Volume or pressure ventilation strategy has to be selected
according to the specific lung disease.
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11. What monitoring parameters are important to
observe when using AutoFlow?
All monitoring used in regular volume controlled modes is also of importance
when using AutoFlow. The set tidal volume has to be adjusted on a regular
basis according to the patient’s needs, most often following arterial blood
gases (ABGs) or according to the end-tidal CO2.
For patient safety, all alarm limits have to be set and should match the current
clinical conditions. Pulmonary changes as well as spontaneous breathing
activities should be observed and monitored carefully. Spontaneous breathing
activity can be seen on the flow curve or on the capnogram. No high Paw
alarm will activate on active expiration. In addition, resistance and compliance changes affect ventilation pressures and flow curves.
In activating AutoFlow the peak pressure will decrease as flow decelerates.
Pinsp will adjust when compliance alters. As a result mean airway pressure
will follow accordingly. The tidal volume applied may vary slightly but
the average volume equals set tidal volume. Therefore changes in airway
resistances are not seen in the pressure curve but influence the flow pattern
significantly when AutoFlow is active. If airway resistances increase it will
take longer to apply and to release a certain amount of volume.
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Peak pressure
decreases with
decelerating
flow
No high Paw
alarm on
spontaneous
breathing
Pinsp adjusts
to compliance
Paw
Paw
Pinsp. = f (V T,C)
PEEP
t
TI
TE
1
f
Flow
VT
t
without spontaneous breathing
Spontaneous
breathing
activity seen on
flow curve
D-9570-2009
Trends give
best overview
with spontaneous breathing
If the VT is not delivered a VT low alarm or MV low alarm is generated.
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12. What safeguards are there against
hypo/hyperventilation?
As in all ventilation modes Minute Volume High and Low alarms are obligatory
to ensure that the patient is adequately ventilated. In case of triggered
modes the respiratory rate is monitored by the High Respiratory Rate alarm.
The High Airway Pressure alarm warns in case of extreme coughing or
obstruction.
In addition AutoFlow offers the following three safeguards:
– If the VT that is supplied to the patient exceeds the set VT by 30%, the inspiratory phase is automatically terminated. This prevents too high a VT being
delivered, in case of, for example, a rapid increase in compliance.
– Rapid triggering by the patient does not lead to hyperventilation in the
modes VC-SIMV/AF and VC-CMV/AF. If hyperventilation occurs in the mode
VC-AC/AF the trigger can be turned off. In that case the patient is still able
to breathe spontaneously.
– If lung compliance changes, AutoFlow adjusts the inspiratory pressure,
breath by breath, by a maximum of 3 mbar/cmH20 per breath. The
maximum inspiratory pressure is limited to 5 mbar/cmH20 below the set
Pmax. If the set VT cannot be reached due to this pressure limit, AutoFlow
provides the alarm “VT low, pressure limit”.
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13. What is the value of AutoFlow in patients with
head injury or stroke?
In patients with head injury or stroke it is of utmost importance to prevent
secondary brain damage due to hypoxia, hypoperfusion or increased intracranial pressure (ICP). When these patients are unconscious (Glasgow
Coma Scale 8 or below), there is an indication for endotracheal intubation
and ventilation.
In volume controlled ventilation PaCO2 levels are maintained, which is
important in preventing additional brain injury. However, in case of volume
controlled ventilation without AutoFlow, there is a risk that the patient has
spontaneous breaths, which can cause high airway pressures, followed by
high intrathoracic pressures and possibly followed by high intra-cranial
pressures, which should be avoided at all times.
Furthermore, when the patient has pulmonary injury in combination with
head injury, the airway pressures should be maintained as low as possible for
the same reasons.
AutoFlow could be applied to patients with head injury or stroke who are
ventilated in a volume controlled mode because the airway pressures will
be as low as possible and spontaneous breathing of the patient is possible
without the rise in airway pressure.
Finally, when AutoFlow is used, there is less need for deep sedation, which
improves neurologic control of the case of patients with head injury or stroke
and has fewer negative circulatory side effects.
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14. What is the value of AutoFlow after return of
spontaneous circulation (ROSC)?
In the period after ROSC (after CPR), the patient’s circulation is very fragile
and therefore ventilation should be performed carefully. Because there is
evidence that manual (bag) ventilation may cause hyperventilation with a
worse outcome, mechanical ventilation is recommended for better control of
ventilation and prevention of hyperventilation and high airway pressures.
Especially during this phase, AutoFlow could help to avoid the above
mentioned side effects and might help to improve outcome after ROSC.
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15. What is the value of AutoFlow in blunt thoracic
trauma?
These patients are at high risk of developing acute lung injury or ARDS and
ventilator associated complications. Airway pressures should be kept low
in thoracic trauma to avoid increasing a pneumothorax even leading to a
tension pneumothorax.
Also, in case of a pulmonary contusion, improvement of outcome can be
achieved when spontaneous ventilation can be maintained.
For these reasons, AutoFlow can be applied when patients with thoracic
trauma have to be ventilated in a volume controlled mode.
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16. What is the value of AutoFlow in patients who
are ventilated via a supraglottic airway?
The number of patients that are ventilated via a supraglottic airway (LMALaryngeal Mask Airway, Larynxtube etc.) is increasing in emergency care.
A supraglottic airway does not totally secure the airway but it is recognized as
the second best step when endotracheal intubation is not possible or fails.
When higher airway pressures are used, there is a risk of leakage around the
cuff and gastric insufflation may occur.
In case of mechanical ventilation in a volume controlled mode, AutoFlow can
be used as it enables control of airway pressures and spontaneous breathing
is possible without excessive airway pressures which would cause the patient
to “fight the ventilator”.