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Mechanical VentilationNov 2003

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Ventilator Review

Standard Ventilation Modes Ventilator Specific ModesDrager Autoflow Review

© 2003, Kim Cooper Salinger, MBA, RRT


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Focus

This review is geared specifically for those who work with the ventilators at VA Palo Alto, but also includes information on other ventilators for those who work at other facilities. Emphasis is on those ventilators and modes of ventilation that are considered the most current and progressive.

VA Palo Alto Respiratory Care Dept. uses the following ventilators:

You will most often see the Drager E4, as it is the most sophisticated ventilator available and offer superior features. The second most frequently used ventilator is the Servo 300, which offers most of the modes found on the Drager, but under different names. The 7200, often referred to as the “old work-horse” is still a great ventilator, but does not offer the more advanced modes found on the new generation ventilators, such as the E4 and 300.

Hospital Policy Regarding Ventilator Adjustments:

Per VA Palo Alto policy, only RCP’s, Fellows, and Attending physicians can make changes or adjustments to ventilator parameters. If a Fellow or Attending makes a change they must notify the RCP immediately. This is due to the variety of ventilators currently on the market and their very different functioning. Frequently changing one parameter will cause other parameters to change as well, and which parameters are affected vary from ventilator to ventilator, and mode to mode. Thus, the safety of the patient is at stake unless a practitioner fully versed in the specific functioning of each ventilator is responsible for manipulations.

Defining difference between RCP’s and RN’s:

RCP’s receive the same minimum amount of schooling as RN’s, however, their educational focus is the pulmonary system. RCP’s have several years of respiratory training with emphasis on ventilator management for optimal patient outcomes, whereas Nursing is more general, with an overview of all the systems. Both RN’s and RCP’s must pass rigorous national board exams in addition to qualifying for individual state licensure.

Modes of Ventilation:


Drager Evita 4 (E4)

Servo 300 LTV 1000 PB 7200

Based on a study conducted by Indiana University, and verified as applicable in the state of California by the Respiratory Care board, The "mean" time spent teaching "mechanical ventilation" is:

Classroom Hours Lab Hours Clinical Hours 1.6 .71 10.2 in the Associate Degree Nursing Programs; 2.2 1.30 41.5 in the Diploma (3-year) Nursing Programs; 1.5 .72 14.9 in the Baccalaureate Degree Nursing Programs, and 44.8 33.00 227.8 in the Respiratory Therapy Program.


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Modes of ventilation are developed and named by the ventilator manufacturer. This means each ventilator can have a different name for the same mode of ventilation, or a similar mode of ventilation. This can be especially troublesome for those who work at multiple facilities with different ventilators in use.

Standard modes of ventilation:

SIMV – synchronized intermittent mandatory ventilation

The vent gives a set number of breaths at a set Vt. In between the patient can take breaths on their own at whatever size tidal volume they want. The pressure it takes to deliver the set VT breaths is variable.

PC – Pressure control

The vent gives a set number of breaths at a set pressure. The Vt is variable – depending on how much air the vent can push in with the set pressure amount. A decelerating waveform is used.

PS- Pressure support

This mode is for spontaneous breathing. It gives a “boost” of pressure to help the patient’s spontaneous breathing efforts. Typically this is used to help support the spontaneous breaths due to the extra work involved in breathing through a small tube.

PEEP – Positive end expiratory pressure

This is pressure that is always in the airway and is never fully exhaled to zero. So at the end of expiration there is still a certain air pressure in the lungs. Leaving a certain amount of pressure in the lungs can prevent alveoli units from completely closing on expiration. This helps with oxygenation status.

CPAP – Continuous positive airway pressure

The same thing as peep, just a different name. The term CPAP is typically used when it is used completely alone. The term peep is used when it is coupled with another mode of ventilation.

Machine Specific Modes of Ventilation:

BiPAP – This is setting two pressure levels,– one for inspiration and one for expiration (pressure support & peep). For example, on inspiration the breath gets a boost of 10, on expiration, the pressure is maintained at 5. Typically this name is used to describe a person being ventilated non-invasively (by mask vs. intubated). A particular manufacturer holds registration on the name using the small i for use on BiPAP non-invasive machines.

BIPAP, Bilevel positive airway pressure – European term, Dragers & PB 840 In this case the term is applied to using pressure control and pressure support together – you will frequently see this usage in European studies and journals. However, PB 840 uses it to refer to APRV also, dependent upon where you set the upper and lower pressure levels.

IPAP and EPAP – Inspiratory positive airway pressure and Expiratory positive airway pressureUsed exclusively with non-invasive ventilation. The IPAP would correspond to a Pressure support limit, and the EPAP would correspond to PEEP. The IPAP is the maximum limit of pressure COMBINED with the PEEP, instead of the amount of positive pressure delivered above the PEEP. So, and IPAP of 10 with an EPAP of 5, would actually be equivalent to Pressure support of 5 with peep of 5.



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AUTOFLOW – Only with Drager ventilators (also see detailed info at the end of this packet)

Two Features:

1. Allows synchronization with patient’s inspiratory and expiratory efforts. Decreases “fighting the vent”.2. Allows you to set a Vt and deliver it at the very lowest possible pressure via a decelerating waveform (huge

benefit). This feature is referred to as PRVC – pressure regulated volume control, in Siemens Servo ventilators.

3. Delivers each breath at the plateau pressure level – thus, what you see as the peak pressure reading is actually the plateau pressure.

With autoflow, The patient can exhale and inhale at any point during the inspiratory or expiratory phase, so there is complete synchrony. Without autoflow, the patient cannot do this, this causes fighting and ‘bucking’ the vent, patient anxiety, the feeling of air hunger for the patient. Flow is variable to meet patient demand.

APRV – Airway Pressure Release Ventilation (Drager & PB 840*)This allows spontaneous breathing on 2 pressure levels and is identical to Pressure Controlled Inverse Ratio Ventilation. The majority of the spontaneous breathing is on an elevated baseline (15 of peep for example), with “release” breaths every so often that go down to the lower set pressure level (5 of peep for example). This is the most common mode of ventilation in Europe, and has excellent outcomes. *The PB 840 refers to this mode of ventilation as Bi-Level Ventilation.

ATC – Automatic Tube Compensation (Drager)A test of weanability. Due to variable inspiratory flow rates, no single level of pressure support can actually fully compensate for work of breathing caused by the ET tube. This mode uses known static resistance for each size and type of ET tube/Trach tube, and measures flow rates to assure adequate levels of pressure support are delivered to compensate for resistance. Also referred to as “electronic extubation”. To be utilized at Stanford in exclusively in conjunction with spontaneous breathing trials.

PRVC – Pressure Regulated Volume Control (Servo 300 & Servo i)This mode is specific to the Siemens Servo ventilators. It allows you to set the desired Vt and using a decelerated waveform, deliver this volume at the lowest possible pressure. It is like Autoflow, except it does not offer the benefit of easily initiated active inspiration/expiration by the patient, and as it is a “control” mode, all breaths are regulated to meet the target tidal volume.

Volume Support – (Servo 300 & Servo i)Volume Support is really pressure support in which the level of pressure is automatically adjusted to achieve a preset target volume. The level of volume (pressure) support can change by as much as 3 cm H20 with each breath until the delivered tidal volume is equal to the target volume. If the patient's compliance improves and the target volume is exceeded, the pressure support level drops by as much as 3 cm H20 at a time to maintain the desired volume.

Automode - (Servo 300 & Servo i)When Automode is enabled, it allows the ventilator to switch between volume control/volume support (VC/VS), pressure control/pressure support (PC/PS), and pressure-regulated volume control/volume support (PRVC/VS) modes with spontaneously triggered breaths. When Automode is activated, the ventilator switches to the corresponding support mode after the patient triggers 2 consecutive breaths. The ventilator remains in the support mode as long as the patient continues to breathe spontaneously. If the patient stops triggering, the ventilator automatically switches back to the clinician-selected control mode.

MMV – (Drager E4, Hamilton Veolar)MMV allows you to set standard parameters, however, it will allow the patient to breath completely spontaneously – setting their own rate and tidal volume – provided they meet the minimum minute volume and/or tidal volume as would be delivered by the ventilator if using the parameters that are set. If the patient begins to not meet that level, the ventilator will increase the pressure support to increase the Vt, or add in machine breaths here and there as needed to meet the level. If the patient has no spontaneous effort, the machine ventilates in accordance with the set parameters. A great weaning mode.



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Some of the other ventilators you might encounter:

Additional Ventilator notes:

What effects what –

1. FiO2 and PEEP are what primarily effect oxygenation2. Rate and Vt are what primarily effect CO2, with rate having the greater influence.4. High plateau and peak pressure is what causes most lung damage & ARDS. (Plateau

pressure is a better indicator of the airway pressures, in Autoflow and PRVC there is no difference between the Peak and Plateau pressures because of how the modes operate. So what you see for peak pressure is actually plateau pressure), Smaller VT’s, PC mode, Autoflow and PRVC are the best methods to keep pressures down.

5. Latest research indicates 6-8cc/kg is the optimal Vt setting to prevent ARDS and lung damage. A higher rate is used to achieve the best minute volume.

6. Vt – Tidal volume. The amount of air that goes in and out with a normal breath.7. V – Minute volume. The amount of air going in and out over a one minute period. A

product of rate and Vt. 8. I-time – how long it takes the breath to go in9. E-time – how long it takes the breath to go out10.TCT – total cycle time. The I-time and E-time combined to give you the time for the full

breath.11.MAP – Mean airway pressure. Average pressure during the total cycle time.12. Tips:

a. oxygenation guideline – when weaning a patient that had high FiO2 & high peep (say 90% O2 & PEEP of 12, wean your oxygen to no lower than 60% before decreasing peep.

b. Spontaneous breathing patients feel best, stress out less, and fight the vent the least in the following modes: SIMV with Autoflow, MMV, Automode, Volume Support, and APRV. (All modes that give the patient more control without sacrificing the quality of ventilation.)

c. Pressure control is a great mode in special circumstances, however, new generation ventilators offer superior modes with all the benefits of PC without the drawbacks. (SIMV with Autoflow & APRV are great examples – chat with your RCP for more info.)


PB 840 Draeger Dura Servo i Hamilton Veolar


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Drager SIMV with Autoflow -The mode most often misunderstood:

AUTOFLOW SUMMARY DESCRIPTION:

Available on the Drager Evita VentilatorsAutoFlow is a feature of the Evita ventilators available in all volume-controlled modes.

Improved synchrony between patient and ventilatorIt allows spontaneous breathing during the entire respiratory cycle, both the insp. and exp. phases. So if the ventilator gives a breath, mid inspiration the patient can exhale if he/she so chooses, or take a bigger breath than the one being delivered by the machine.

Tidal Volume delivered at the lowest possible peak pressure.The ventilator will deliver the set Vt at the lowest pressure possible, automatically regulating inspiratory flow based on the lung mechanics (resistance and compliance) of the patient.

Decelerating flow pattern.This variable flow and responsiveness to changes in lung mechanics creates a decelerating inspiratory flow pattern, as you would see with Pressure Control Ventilation (PCV).

Waveforms identical to Pressure Control Ventilation.The characteristic AutoFlow pressure and flow waveforms are identical to those of PCV, see illustration below.


Pressure ControlVentilation

AutoFlow VolumeVentilation

Standard VolumeVentilation

Flow Waveforms

Pplat

Vt

Pplat

Vt

Figure 8


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Each breath is delivered at Plateau Pressure levelThe pressure waveform with AutoFlow does not show a different level for PIP and Pplateau. That is because the breath is delivered at the level of pressure typically measured as the Pplateau. There is no extra pressure utilized to deliver the breath, so there is no difference between PIP and Pplateau with Autoflow.

Pressure is adjusted breath by breath in response to lung compliance changesThe pressure used to deliver the AutoFlow breath varies with changes in lung mechanics as needed. These changes occur in increments of 1 to 3 cm H2O, between successive ventilator breaths.

Advantage of Autoflow over Pressure ControlWith PCV, changes in compliance can lead to a decrease in delivered tidal volume while the set pressure remains constant. This reduced tidal volume will continue unless recognized by the clinician or a ventilator alarm function (low VE). AutoFlow, in the presence of decreased compliance will incrementally increase the pressure needed to deliver the breath until the set Vt is restored.

*NOTE: If you see the “VOLUME NOT CONSTANT” alarm/message, it indicates that the PIP has reached 5 cm H2O of the set pressure limit alarm. Transient decreases in minute ventilation may occur as Autoflow adapts to these changes.


Gradual increase in pressure by 1-3 cmH2O in response to compliance changes using Autoflow

Pressure Control Ventilation assures constant pressure, however loses Vt with decreased lung compliance

FLOW

PRESS

Volume Ventilation

Without AutoFlow

With AutoFlow

Pplateau

AutoFlow delivers Vt using the Pplateau level of pressure

PIP

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Documents

ventilator parameters

ventilator adjustments

standard modes of ventilation

ventilator management

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