Advanced Modes of Mechanical Ventilation

Advanced Modes of Mechanical Ventilation

Michael Haines, MPH, RRT-NPS, AE-CVictor Valley Community College

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What we will cover…– Intro to advanced modes– PRVC– Automode– Volume Support/Variable Pressure– Autoflow– Adaptive Support Ventilation– Volume assured pressure support (VAPS)– Automatic Tube compensation– Mandatory Minute Ventilation – Proportional Assist Ventilation – BUT FIRST A LITTLE REVIEW….

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• Ventilator Formulas

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http://www.youtube.com/watch?v=VucJeaX8LOk

elastance = pressure / volume

volume

transairwaypressure

transthoracicpressure

transrespiratorypressure

Lung Mechanics

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resistance = pressure / flow

flow

Static Compliance• Cs = tidal volume corrected for gas compression Pplat – PEEP total peepNormal 100 - 200 ml / cmH2O (PDQ)Decreased with:• Mainstem Intubation• Congestive Heart Failure• ARDS• Atelectasis• Consolidation• Fibrosis• Hyperinflation• Tension Pneumothorax• Pleural Effusion• Abdominal Distension• Chest Wall Edema• Thoracic Deformity

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Principle #1: VentilationThe goal of ventilation is to facilitate CO2 release and maintain a normal PaCO2

Minute Ventilation (Ve)– Total amount of gas exhaled per minute– Ve = Vt x f– Ve comprised of 2 factors

VA = alveolar ventilation VD = dead space ventilation

Ventilation in the ICU setting– Increased CO2 production

Fever, sepsis, injury, overfeeding– Increased VD

Vent circuit, ET tube Adjustments: Vt and f

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Fig. 13-1. Factors that affect the partial pressure of arterial carbon dioxide (PaCO2) during mechanical ventilation. V.CO2, carbon dioxide production; V.A, alveolar ventilation; V.E, minute ventilation; V.D, dead space ventilation; VT, tidal volume; TI, inspiratory time; TE, expiratory time; f, respiratory rate. (From Hess DR, MacIntyre NR, Mishoe SC, et al: Respiratory care principles and practice, Philadelphia, 2002, WB Saunders.)

Principle #2: OxygenationThe primary goal of oxygenation is to maximize O2 delivery to the blood (PaO2)

Alveolar-arterial O2 gradient– Equilibrium between O2 in the blood and O2 in the alveoli– A-a gradient measures efficiency of oxygenation– PaO2 partially depends on ventilation but more on V/Q

matching Oxygenation in the ICU setting– PaO2/PAO2 ratio (a/A ratio)

Indicator of efficiency of O2 transport– CaO2

Adjustments: FiO2 and PEEP

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Volume vs. Pressure Control Ventilation

Volume Ventilation• Volume delivery constant

• Inspiratory pressure varies

• Inspiratory flow constant

• Inspiratory time determined by set flow and Vt

Pressure Ventilation• Volume delivery varies

• Inspiratory pressure constant

• Inspiratory flow varies

• Inspiratory time set by clinician

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What’s Wrong with Volume Control Ventilation?

• The limited flow may not meet the patient’s desired inspiratory flow rate

• If the patient continues to inspire vigorously -- , added, unnecessary work is done– Can lead to fatigue

• Can cause excessive airway pressure leading to barotrauma, volutrauma, and adverse hemodynamic effects

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Pressure Control Ventilation:The Alternative

• Definition– The application of clinician-set inspiratory pressure and inspiratory

time. Flow delivery varies according to patient demand

• The clinician sets the inspiratory pressure, I-time or I:E ratio and RR

• Tidal volume varies with changes in compliance and resistance

• Flow delivery is decelerating

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Pressure Control Ventilation

• May be used in A/C and SIMV modes

• In A/C - all breaths (either machine-initiated or patient-initiated) are time-cycled and pressure-limited

• In SIMV - only machine-initiated breaths are time-cycled and pressure-limited– Spontaneous breaths can be pressure-supported

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Pressure Control Ventilation• Advantages

– Limits risk of barotrauma– May recruit collapsed and flooded alveoli– Improved gas distribution– Uses a active exhalation valve which uses servo-control

technology that allows gas to be released from the exhalation valve during the inspiratory phase if the patient makes an expiratory effort.

• Disadvantages– Tidal volumes vary when patient compliance changes (i.e.,

ARDS, pulmonary edema)– With increases in I-time, patient may require sedation and/or

chemical paralysis

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Indications for PCV

• Enhance patient / ventilatory synchrony– Patient determines flow

• Lung protection strategy– Lower inspiratory pressure with decelerating flow may

improve V/Q matching– Adjusting I-time may improve oxygenation

by ↑ MAP• Alveolar diseases that produce varying time constants

– May recruit alveoli by lengthening I-time

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Rationale of Pressure Modes

• Ventilator-induced lung injury (VILI)

• Atelectrauma

• Pre-existing lung damage and/or inflammation

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The Cons of Pressure Control

• Variable Vt as pulmonary mechanics change

• Potentially excessive Vt as compliance improves

• Inconsistent changes in Vt with changes in PIP and PEEP

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Most Commonly used Waveforms

• Pressure vs. Time

• Flow vs. Time

• Volume vs. Time

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Pressure-Time Curve

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1 2 3 4 5 6

20

Sec

PawcmH2O

Pressure Ventilation

Expiration

Volume Ventilation

Pressure vs. Time Curve

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1 2 3 4 5 6

30

Sec

PawcmH2O

A BC

PIP

Baseline

Mean Airway Pressure

-10

If compliance decreases the pressure increases to maintain the same Vt

Volume Control Breath TypesVolume Control Breath Types

11 22 33 44 55 66

SECSEC

11 22 33 44 55 66

PPawaw

cmHcmH2200

6060

-20-20

120120

120120

SECSEC

INSPINSP

EXHEXH

FlowFlowL/minL/min

20

Inspiration Expiration

0 1

20

00 1 2

3

-3

0

20

021

20

00 1 2

3

-3

0

20

02

Inspiration Expiration

Volume/Flow Control Pressure Volume/Flow Control Pressure ControlControl

Time (s) Time (s)

PawPaw

Pressure

Volume

Flow

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• These curves illustrate the two basic approaches to ventilator control. If the ventilator controls flow, it controls volume indirectly (by definition) and vice versa. Usually, inspiratory flow is held constant during inspiration, causing volume and pressure to rise linearly. Inspiration ends (cycles off) when a preset tidal volume is met.

• In contrast, with pressure control ventilation, airway pressure may be held constant during inspiration. This causes inspiratory flow to decay exponentially from its peak value towards zero as volume rises exponentially. Inspiration usually ends after a preset inspiratory time or (in the case of pressure support) after a preset inspiratory flow threshold has been crossed. If inspiratory time is long enough (usually about 5 time constants) lung pressure will equilibrate with airway pressure and inspiratory flow will cease.

• You will note that for passive exhalation is exponential. That mean expiratory time must be at least 5 time constants long to exhale more that 99% of the tidal volume. As expiratory time becomes shorter than 5 time constants, gas trapping (ie, autoPEEP) occurs.

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Work to Trigger

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1 2 3 4 5 6

30

Sec

PawcmH2O

-10

Assisted Breath

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Lung Overdistension

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Analysis of Compliance Waveforms Compliance waveforms

simultaneously display volumes and the amount of pressure necessary to deliver these volumes. Volume normally is plotted on the “Y” axis and pressure on the “X” axis.

The curve to the right depicts a compliance curve from a patient with normal compliance and airway resistance. The arrow pointing down and to the left is on the expiratory side of the curve.

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Analysis of Compliance Waveforms

• One of the clinical indications for the addition of positive-end expiratory pressure (PEEP) is low lung compliance. If PEEP is added, the baseline pressure would then be elevated and the curve would shift to the right.

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Altering Compliance with PEEP• The curve drawn in a heavy, non-dashed line represents an improved lung

compliance due to the addition of PEEP. Notice that the tidal volume is the same (note the “Y” axis) while the PIP has fallen (note the “X” axis). Since the same volume is delivered with less of a pressure difference (PIP-PEEP), compliance has increased.

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Compliance Curves The following series of

compliance curves reflect a steady fall in lung compliance, as would occur with the development of cardiogenic or noncardiogenic pulmonary edema. The first curve (1) reflects the patient’s baseline condition. As his compliance falls, higher pressures are needed to deliver the same tidal volume (2) (second set of curves with the initial curve indicated in gray). As the patient’s condition deteriorates further, the final compliance curve is obtained (3).

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Assist/Control Mechanical Ventilation

Notice that the third mechanical breath was preceded by a drop in airway pressure (indicating a spontaneous inspiratory effort). In addition, note that the TCT had not elapsed prior to the initiation of this breath. Although only one of the breaths was initiated spontaneously, all breaths had the same tidal volume.

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Synchronized Intermittent Mandatory Ventilation (SIMV)

Notice that the fifth breath was a mechanical breath that was initiated by a spontaneous inspiratory effort. If this effort had occurred before the sensitivity window began, the patient would have only had a spontaneous, unassisted breath (circled). In addition, notice that the therapist selected a constant flow pattern for this patient.

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Support Ventilation (PSV)

• Salient features of the flow graph:– The amount of inspiratory flow may vary from breath to

breath based on patient inspiratory effort (V1<V2).– Duration of each breath may vary.– http://www.youtube.com/watch?v=Rwr5ZjJI1ZQ

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http://www.youtube.com/watch?v=Rwr5ZjJI1ZQ

Support Ventilation (PSV)

• Salient features of the volume graph:– The tidal volume may vary from breath to breath

based on patient inspiratory effort (V1<V2).– Duration of each breath may vary.

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Pressure, Flow, and Volume Curves A clearer picture of the dynamics

of plateau pressures and inflation holds is obtained when pressure curves are viewed along with their corresponding flow and volume curves. Notice that flowrate drops to zero during the plateau interval, separating expiratory flow from inspiratory flow. In addition, even though flow is not occurring during the inflation hold, the inflation hold is still considered to be part of inspiratory time or Ti. Since no flow is occurring the volume does not change during the pause.

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Pressure vs. Volume Ventilation(From Branson, R., Bird product literature)

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New Modes: Dual Modes

• Between-Breath Adjustment

• Volume Support (VS)

• Pressure-Regulated Volume Control

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• Within-breath Adjustment

• Automatic Tube Compensation (ATC)

• Volume-Assured Pressure Support

Why use newer modes of ventilation?

• Newer ventilators can be set to modes other than the pressure-control and volume-control modes of older machines

• The alternative modes of ventilation were developed to prevent lung injury and asynchrony through patient adaptation, promote better oxygenation and faster weaning, and be easier to use.

• However, evidence of their benefit is scant.• Remember: weaning is a dynamic process requiring

frequent intervention and adjustments, best performed by the RT!

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Why use newer modes of ventilation?

• Technologic advances and computerized control of mechanical ventilators have made it possible to deliver ventilatory assistance in new modes. Driving these innovations is the desire to prevent ventilator induced lung injury, improve patient comfort, and liberate the patient from mechanical ventilation as soon as possible

• We call these innovations “alternative” modes to differentiate them from the plain volume-control and pressure-control modes

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Terminology• APC—adaptive pressure control• APRV—airway pressure-release

ventilation• ASV—adaptive support ventilation• HFOV—high-frequency oscillatory

ventilation• MMV- Mandatory Minute Ventilation• PAV—proportional assist ventilation• PRVC – Pressure Release Volume

Control• PSV—pressure support ventilation• VC+ - Volume control plus• VS- Volume Support

• APV- adaptive pressure ventilation• ATC – Automatic tubing

compensation• VP- variable pressure• VTPC- Volume targeted pressure

control

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• 24% of mechanically ventilated patients exhibit patient-ventilator asynchrony in > 10% of their respiratory efforts during AVC and PS ventilation (ineffective triggering and double triggering).• Patient-ventilator asynchrony

during assisted mechanical ventilationIntensive Care Med. 2006;32:1512

Patient-ventilator Asynchrony

Arnold W. Thille, Pablo Rodriguez, Belen CabelloFrancois Lellouche, Laurent Brochard

1. Kollef M et al. Chest. 1998;114:541–548.2. Levine S et al. NEJM .2008;358:1327-1335.3. Rello J et al. Chest .2002;122:2115-2121.

Length of Stay

Asynchrony

Sedation

Prolonged ventilation

time1

Possible muscle atrophy2 and VAP3

Weaning is delayed

Ventilator asynchrony is manifested in several forms

• Common asynchrony patterns include missed efforts, double triggering and auto-cycling.

• These problems typically occur when the breath parameters set on the ventilator do not match the signals from the patient’s respiratory center in the brain.

• The upper graphic shows multiple missed efforts in the pressure support mode.

• The lower graphic shows an asynchronous pattern called “double trigger” in the assist control mode.

• Because patient conditions are constantly changing, frequent manipulation of the ventilator settings are required to manage the asynchrony. It is not uncommon for patients to be sedated as a result of asynchrony and this has been shown to prolong ventilation time.1

Furthermore, prolonged ventilation time can result in rapid disuse atrophy of the diaphragm2 and ventilator-associated pneumonia.3

Mechanical breath terminology

• Control variable—the mechanical breath goal, ie, a set pressure or a set volume

• Trigger variable—that which starts inspiration, ie, the patient (generating changes in pressure or flow) or a set rate (time between breaths)

• Limit variable—the maximum value during inspiration

• Cycle variable—that which ends inspiration

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Mechanical breath terminology

• Continuous mandatory ventilation—all breaths are controlled by the ventilator, so usually they have the same characteristics regardless of the trigger (patient or set rate); no spontaneous breaths are allowed

• Intermittent mandatory ventilation—a set number of mechanical breaths is delivered regardless of the trigger (patient initiation or set rate); spontaneous breaths are allowed between or during mandatory breaths

• Continuous spontaneous ventilation—all breaths are spontaneous with or without assistance

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Mechanical breath terminology• Set point—the ventilator delivers and maintains a set goal, and this

goal is constant (eg, in pressure control, the set point is pressure, which will remain constant throughout the breath)

• Servo—the ventilator adjusts its output to a given patient variable (ie, in proportional assist ventilation,

• the inspiratory flow follows and amplifies the patient’s own flow pattern)

• Adaptive—the ventilator adjusts a set point to maintain a different operator-selected set point (ie, in pressure-regulated volume control, the inspiratory pressure is adjusted breath to breath to achieve a target tidal volume)

• Optimal—the ventilator uses a mathematical model to calculate the set points to achieve a goal (ie, in adaptive support ventilation, the pressure, respiratory rate, and tidal volume are adjusted to achieve a goal minute ventilation)

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Examples of the first dual modes

• Volume Assured Pressure Support (VAPS) & Pressure Augmentation

• Pressure Regulated Volume Control (PRVC) & similar modes

• Volume Support Ventilation (VS or VSV) & similar modes

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NEW MODES OF VENTILATION DUAL-CONTROLLED MODES

Type Manufacturer; ventilator Name

Dual control within a breath VIASYS Healthcare; Bird 8400Sti and TbirdVIASYS Healthcare; Bear 1000

Volume-assured pressure supportPressure augmentation

Dual control breath to breath:Pressure-limited flow-cycled ventilation

Siemens; servo 300Cardiopulmonary corporation; Venturi

Volume supportVariable pressure support

Dual control breath to breath:Pressure-limited time-cycled ventilation

Siemens; servo 300Hamilton; GalileoDrager; Evita4

Pressure-regulated volume controlAdaptive pressure ventilationAutoflowVariable pressure control

Dual control breath to breath:SIMV

Hamilton; Galileo Adaptive support ventilation

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Dual Control Breath-to-Breathpressure-limited time-cycled ventilation

Pressure Regulated Volume Control

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Servo 300 Maquet Servo-i

Other Names for PRVC…

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AutoFlow (Drager • Medical AG, Lubeck, Germany)Adaptive Pressure Ventilation (HamiltonGalileo, Hamilton Medical AG, Bonaduz, Switzerland)Volume Control+ (Puritan Bennett, Tyco Healthcare; Mansfield, MA)Volume Targeted Pressure Control, Pressure Controlled Volume Guaranteed (Engstrom, General Electric, Madison, WI).

Pressure Regulated Volume Control (PRVC)

• One of the concerns with pressure-control ventilation is that it cannot guarantee a minimum minute ventilation in the face of changing lung mechanics or patient effort, or both.

• To solve this problem, in 1991 the Siemens Servo 300 ventilator introduced Pressure Regulated Volume Control, a mode that delivers pressure-controlled breaths with a target tidal volume and that is otherwise known as adaptive pressure control (APC)

• On the Servo it was initially only available on AC mode

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• PRVC is not a volume-control mode (Despite the name!). In volume control, the tidal volume does not change; in APC the tidal volume can increase or decrease, and the ventilator will adjust the inflation pressure to achieve the target volume.

• Thus, APC guarantees an average minimum tidal volume but not a maximum tidal volume

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• Combines volume ventilation & pressure control– (for mech., time-cycl. breaths only)

• Set TV is “targeted”• Ventilator estimates vol./press. relationship

each breath• Ventilator adjusts level of pressure control

breath by breath

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• Delivers patient or timed triggered, pressure-targeted (controlled) and time-cycled breaths

• Ventilator measures VT delivered with VT set on the controls. If delivered VT is less or more, ventilator increases or decreases pressure delivered until set VT and delivered VT are equal

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• This mode differs from pressure AC by adjusting rhe pressure level on a breath-by-breath basis to ensure a targeted Vt

• The respiratory therapist must set:– Pressure– Target Vt,– Inspiratory time– Backup rate– Rise time– FiO2– PEEP– Sensitivity

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• For each breath, the ventilator assesses each breath and adjusts pressure 1-3 cm H2O and assesses the Vt

• This mode works best for pts who are apneic or have a weak ventilatory drive, used on AC mode and also SIMV (only on Servo I)

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Pressure Regulated Volume Control (PRVC)• First breath = 5-10 cm H2O above PEEP• First breath is a “test breath”, an inspiratory hold

is also applied to obtain a plateau pressure to be applied on the next breath

• V/P relationship measured• Next 3 breaths, pressure increased to 75%

needed for set TV• Then up to +/- 3 cm H2O changes per breath• Time ends inspiration

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The pressure is constant after the first test breath (square pattern) and flow becomes variable with a decelerating ramp pattern just as in pressure control mode.

1st breath

2nd


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PRVC. (1), Test breath (5 cm H2O); (2) pressure is increased to deliver set volume; (3), maximum

available pressure; (4), breath delivered at preset E, at preset f, and during preset TI; (5), when VT

corresponds to set value, pressure remains constant; (6), if preset volume increases, pressure decreases; the ventilator continually monitors and adapts to the patient’s needs

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The vent then regulates the amount of pressure needed to obtain the desired set VT. It will increase or decrease the amount of pressure on a “breath by breath” basis, (+/- 3 cmH2O per breath)

Press increase +3

PRVC flowchart

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Test Breath

Measure tidal

Volume

Decrease Insp

Pressure

More Compare to set Tidal

Volume

LessE

qu

al

Give Same Insp

Pressure

Increase Insp

Pressure

Pressure Regulated Volume Control (PRVC)- Considerations

• Assist-control mode• Like PC, flow varies automatically to varying

patient demands • Constant press. during each breath - variable

press. from breath to breath• Time is cycling method; delivered TV can vary

from set

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Pressure Regulated Volume Control (PRVC)- Considerations

• The ventilator will not allow delivered pressure to rise higher than 5 cm H2O below set upper pressure limit• Example: If upper pressure limit is set to 35 cm H2O and

the ventilator requires more than 30 cm H2O to deliver a targeted VT of 500 mL, an alarm will sound alerting the clinician that too much pressure is being required to deliver set volume (may be due to bronchospasm, secretions, changes in CL, etc.)

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• Indications• Patient who require the lowest possible

pressure and a guaranteed consistent VT• ALI/ARDS—Questionable, ideally change

to PC, VC with low VT/high rate or APRV or HFOV

• Patients requiring high and/or variable I• Patient with the possibility of CL or Raw

changes64

Pressure Regulated Volume Control (PRVC)• Disadvantages and Risks

• Varying mean airway pressure• May cause or worsen auto-PEEP• When patient demand is increased, pressure level may

diminish when support is needed• May be tolerated poorly in awake non-sedated patients• A sudden increase in respiratory rate and demand may

result in a decrease in ventilator support• Pressure delivered is dependent on VT from previous

breath. If patient intermittently makes a significant inspiratory effort, it can result in variable volumes that can be higher or lower than the setting

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In this example, the first breath is a control breath with the patient making no respiratory effort this time. The desired tidal volume of 500 is delivered here.

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The second breath is triggered by the patient who made a significant inspiratory effort. Although, PIP has remained the same as the first breath, a higher tidal volume results because of higher transpulmonary pressure

Pressure unchanged

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The ventilator will then reduce the amount of pressure needed for the next breath. The patient doesn’t make any inspiratory effort with this breath, the result is a tidal volume that is lower than the set tidal volume


• Advantages• Maintains a minimum PIP• Targeted VT and E

• Patient has very little WOB requirement• Allows patient control of respiratory rate and E• Variable E to meet patient demand• Decelerating flow waveform for improved gas

distribution• Breath by breath analysis??

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• Understanding PRVC part 1• Understanding PRVC part 2

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http://www.youtube.com/watch?v=j9qbXnAvLsA

http://www.youtube.com/watch?v=FhG2YPzN6-c

Auto-mode/Volume Support on PRVC

• For patients that are making intermittent inspiratory efforts, or breathing spontaneously, switching to Automode may be better (on Servo, called adaptive support ventilation on Galelio)

• In Automode, the ventilator will automatically switch between PRVC and Volume Support mode.

• PRVC breaths when there is no patient effort and VS breaths with patient effort

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Auto-mode/Volume Support on PRVC

• Volume Support works the same way as PRVC• VS automatically adjusts the level of pressure

support needed to achieve a targeted tidal volume, based on the amount of inspiratory effort given by the patient

• Volume Support is basically, Pressure Support that guarantees a set tidal volume

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VS (Volume Support)• Entirely a spontaneous mode• Delivers a patient triggered (pressure or flow), pressure

targeted, flow cycled breath – Can also be timed cycled (if TI is extended for some reason) or

pressure cycled (if pressure rises too high).• Similar to pressure support except VS also targets set VT. It

adjusts pressure (up or down) to achieve the set volume (the maximum pressure change is < 3 cm H2O and ranges from 0 cm H2O to 5 cm H2O below the high pressure alarm setting

• Used for patients ready to be “weaned” from the ventilator and for patients who cannot do all the WOB but who are breathing spontaneously

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VS (Volume Support)

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(1), VS test breath (5 cm H2O); (2), pressure is increased slowly until target volume is achieved; (3), maximum available pressure is 5 cm H2O below upper pressure limit; (4), VT higher than set VT delivered results in lower pressure; (5), patient can trigger breath; (6) if

apnea alarm is detected, ventilator switches to PRVC

Volume Support (VS)

• Pressure limited• Flow cycled• Automatic weaning of pressure support as

long as tidal volume matches the minimum required to Vt.

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Volume Support (VS)• What happens in VS if impedance changes

(higher resistance or less compliance )?• – TV will decrease, subsequent pressure will be

increased to bring TV back toward the goal.• Little data to show it actually works.• • If pressure support level increases to maintain

TV in pt with increased airways resistance, PEEPi may increase.

• • If minimum TV set too high, weaning may be delayed

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VS (Volume Support)

• Advantages• Guaranteed VT and E• Pressure supported breaths using the lowest

required pressure• Decreases the patient’s spontaneous respiratory

rate• Decreases patient WOB• Allows patient control of I:E time• Breath by breath analysis• Variable I to meet the patient’s demand

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VS (Volume Support)

• Disadvantages• Spontaneous ventilation required• VT selected may be too large or small for

patient• Varying mean airway pressure• Auto-PEEP may affect proper functioning• A sudden increase in respiratory rate and

demand may result in a decrease in ventilator support

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Auto Flow-on Drager

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Essentially the same as PRVC: Autoflow is not a specific mode, it can be used with all volume modes, and is effective during the inspiratory phase.• Autoflow converts a volume mode to a volume targeted, pressure limited mode. The goal is to deliver the set tidal at the lowest possible pressure (plateau pressure) utilizing a decelerating gas flow pattern. •Autoflow allows the exhalation valve to behave as a CPAP valve (threshold resistor) allowing the patient to alter their flow patterns, enhancing the ability to breathe spontaneously.•During the inspiratory period the patient is able to exhale, cough or sigh.

Auto Flow-on Drager• When autoflow is activated, a test breath is delivered at a

pressure of 5 cmH20 above PEEP. The second breath is delivered at 75% of the set tidal volume. The third breath will be the set tidal volume, provided the pressure is 3 to 5 cmH20 below the pressure limit.

• The microprocessor algorithm then calculates the minimal pressure capable of achieving the targeted tidal volume. Autoflow recalculates compliance with each breath, and the next breath reflects any change in compliance. As the patients lung compliance changes, the pressure will adjust up or down in increments of no more than 3 cmH20 per breath.

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Adaptive Support Ventilation-

• Adaptive support ventilation (ASV) evolved as a form of mandatory minute ventilation implemented with a daptive pressure control.

• ASV delivers pressure-controlled breaths using• an adaptive (optimal) scheme “Optimal,” in this

context, means minimizing the mechanical work of breathing: the machine selects a tidal volume and frequency that the patient’s brain would presumably select if the patient were not connected to a ventilator.

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Adaptive Support Ventilation- Galileo vent

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A dual control mode that uses pressure ventilation (both PC and PSV) to maintain a set minimum Ve (volume target) using the least required settings for minimal WOB depending on the patient’s condition and effort. It automatically adapts to patient demand by increasing or decreasing support, depending on the patient’s elastic and resistive loads


• The clinician enters the patient’s IBW, which allows the ventilator’s algorithm to choose a required Ve. The ventilator then delivers 100 mL/min/kg. A series of test breaths measures the system C, resistance and auto-PEEP

• If no spontaneous effort occurs, the ventilator determines the appropriate respiratory rate, VT, and pressure limit delivered for the mandatory breaths

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• The ventilator initially delivers test breaths, in which it measures the expiratory time constant for the respiratory system and then uses this along with the estimated dead space and normal minute ventilation to calculate an optimal breathing frequency in terms of mechanical work.

• The optimal or target tidal volume is calculated as the normal minute ventilation divided by the optimal frequency.

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• I:E ratio and TI of the mandatory breaths are continually being “optimized” by the ventilator to prevent auto-PEEP

• If the patient begins having spontaneous breaths, the number of mandatory breaths decrease and the ventilator switches to PS at the same pressure level

• Pressure limits for both mandatory and spontaneous breaths are always being automatically adjusted to meet the Ve target

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ASV: Principle mode of ventilation

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Pinsp

PEEP

no patient activity:* machine triggered+ time cycled

patient is active:* patient triggered+ flow cycled

Flow I

Flow E * *

+ +

From Hamilton Medical


• The target tidal volume is achieved by the use of APC This means that the pressure limit is automatically adjusted to achieve an average delivered tidal volume equal to the target. The ventilator continuously monitors the respiratory system mechanics and adjusts its settings accordingly.

• The ventilator adjusts its breaths to avoid air trapping by allowing enough time to exhale, to avoid hypoventilation by delivering tidal volume greater than the dead space, and to avoid volutrauma by avoiding large tidal volume

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: Hamilton Galileo’s ASV - Considerations

• If pt.’s f > “set” by vent., mode is PS• If pt.’s f < “set” by vent., mode is PC-SIMV/PS• If patient is apneic, all breaths are PC

• Mandatory breaths = PC, pt. triggered = PS– both at same targeted TV and calculated press.

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Ventilator settingsin adaptive support ventilation

• Ventilator settings in ASV are:• Patient height (to calculate • the IBW), Sex• Percent of normal predicted minute ventilation goal• Fio2• PEEP• Clinical applications of adaptive support

ventilation• ASV is intended as a sole mode of ventilation,• from initial support to weaning.

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Theoretical benefits of adaptive support ventilation

• In theory, ASV offers automatic selection of ventilator settings, automatic adaptation to changing patient lung mechanics, less need for human manipulation of the machine, improved synchrony, and automatic weaning

• Physiologic benefits. Ventilator settings are adjusted automatically. ASV selects different tidal volume-respiratory rate combinations based on respiratory mechanics in passive and paralyzed patients

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Clinical Evidence for ASV• In actively breathing patients, there was no difference in

the ventilator settings chosen by ASV for different clinical scenarios (and lung physiology).10 Compared with pressure-controlled intermittent mandatory ventilation, with ASV, the inspiratory load is less and patient-ventilator interaction is better

• Two trials suggest that ASV may decrease time on mechanical ventilation. However, in another trial,16 compared with a standard protocol, ASV led to fewer ventilator adjustments but achieved similar postsurgical weaning outcomes.

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Disadvantages ASV

• Inability to recognize and adjust to changes in alveolar VD

• Possible respiratory muscle atrophy• Varying mean airway pressure• In patients with COPD, a longer TE may be

required • A sudden increase in respiratory rate and

demand may result in a decrease in ventilator support

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Clinical Evidence for ASV• Adaptive support ventilation: Bottom line• ASV is the first commercially available mode• that automatically selects all the ventilator• settings except PEEP and Fio2. These seem• appropriate for different clinical scenarios• in patients with poor respiratory effort or in• paralyzed patients. Evidence of the effect in• actively breathing patients and on outcomes• such as length of stay or death is still lacking

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• Initializing ASV• ASV in Obese patient

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http://www.youtube.com/watch?v=zB_hmHzPN1A&list=PL5ac77OUcT0w3FoH1jV8ByBjKncmNMNDX

http://www.youtube.com/watch?v=Mbw72GaPgWw&list=PL5ac77OUcT0w3FoH1jV8ByBjKncmNMNDX

Volume Assured Pressure Support (VAPS)

• Designed to reduce work of breathing while maintaining a minimum minute volume and a minimum Vt

• Combines a high initial flow as in PC and a constant volume delivery as in VC

• This mode allows a feedback loop based on tidal volume

• Switches even within a single breath from pressure control to volume control if minimum tidal volume has not been achieved

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• The respiratory therapist sets:– Pressure limit = plateau seen during VC– RR– Peak flow rate– PEEP– FiO2– Trigger sensitivity– Minimum tidal volume– Also called AVAPS used in NPPV on Respironics Bipap

97

PPawaw

cmHcmH2200

6060

-20-20

6060

FlowFlowL/minL/min

VolumeVolume

Set flow limit

Set tidal volume cycle threshold

Set pressure limit

Tidal volume met

Tidal volume not met

Switch from Pressure control toVolume/flow control

Inspiratory flowgreater than set flow

Flow cycleInspiratory flowequals set flow

Pressure limitoverridden

LL

0

0.6

4040

98

Volume Assured Pressure Support (VAPS) Limitations

• If pressure too high, all breaths are pressure limited

• If peak flow is set too low, the switch from pressure to volume is late in the breath, inspiratory time is too long.

• Once a breath is triggered, rapid, variable flow pushes pressure to reach set pressure support level.

• Tidal volume delivered from the machine is monitored.

99


• Combines volume ventilation & pressure support

– (for mech., vol. limited breaths only)• Uses TV, peak flow, and pressure sup./control settings• Targets PS level with at least set peak flow first• Continues until flow decreases to set peak flow, then:

– If TV not delivered, peak flow maintained until vol. limit

– If TV or more delivered, breath ends

100

VAPS: Volume Assured Pressure Support

101 (From Branson, R., Bird product literature)(From Branson, R., Bird product literature)

VAPS: (and Pressure Augmentation) - Considerations

• The set TV is the minimum TV the patient will receive

• The set pressure support is the minimum the patient will receive

• The set peak flow is the minimum the patient will receive

• No ventilatory mechanics measured

102

VAPS vs. VS

• How does volume support differ from• VAPS ?

– In volume support, we are trying to adjust pressure so that, within a few breaths, desired TV is reached.– In VAPS, we are aiming for desired TV tacked on to the end of a breath if a pressure-limited breath is going to fail to achieve TV

103

Automatic Tube Compensation (ATC)

• Additional Work of Breathing

– Tube resistance causes the highest workload for patients with normal lung mechanics

– Tube resistance is proportional to the flow

– Tube resistance increases with smaller tubes

– New Modes of Ventilatory Support in Spontaneously Breathing Intubated Patients by Stocker et al, Yearbook of Intensive Care and Emergency Medicine 1997: 514-533

104


• How Does It Work?

– The spontaneously breathing intubated patient has to perform work of breathing to overcome the tube resistance

– ATC takes over the work of breathing induced by the tube resistance

– The patient breathes like without any tube

– Respiratory comfort of automatic tube compensation and inspiratory pressure support in conscious humans by Guttman, J. et al, Intensive Care Medicine 1997, Vol. 23, No. 11, 1119-1124

105


• Benefits

– Patient comfort• ATC adjusts on-line the pressure to compensate the

pressure drop over the tube caused by the current inhaled gas flow of the patient

– Stocker et al have suggested that a patient’s breathing during ATC looks like it would if the patient was extubated – “electronic extubation”• Cannot predict airway patency, after extubation

106

107

With ATC switched ON, if patient inhales with a higher flow rate, Evita increases the support pressure within the breath and vice versa. The pressure is automatically adjusted in real time about 200 times within an inspiration. Thus ATC compensates for the resistive work load of the endotracheal tube. Patient experiences "Virtual Extubation".

MMV (Mandatory Minute Ventilation)

• AKA: Minimum Minute Ventilation or Augmented minute ventilation

• Operator sets a minimum E which usually is 70% - 90% of patient’s current E. The ventilator provides whatever part of the E that the patient is unable to accomplish. This accomplished by increasing the breath rate or the preset pressure.

• It is a form of PSV where the PS level is not set, but rather variable according to the patient’s need

108


• Indications– Any patient who is spontaneously and is

deemed ready to wean– Patients with unstable ventilatory drive

• Advantages– Full to partial ventilatory support– Allows spontaneous ventilation with safety

net– Patient’s E remains stable– Prevents hypoventilation

109


• Disadvantages• An adequate E may not equal sufficient A (e.g.,

rapid shallow breathing)• The high rate alarm must be set low enough to

alert clinician of rapid shallow breathing• Variable mean airway pressure• An inadequate set E (>spontaneous E) can

lead to inadequate support and patient fatigue• An excessive set E (>spontaneous E) with no

spontaneous breathing can lead to total support

110

PAV (Proportional Assist Ventilation)

• Patients who have normal respiratory drive but who have difficulty sustaining adequate spontaneous ventilation are often subjected to pressure support ventilation (PSV), in which the ventilator generates a constant pressure throughout inspiration regardless of the intensity of the patient’s effort.

• In 1992, Younes and colleagues19,20 developed proportional assist ventilation (PAV) as an alternative in which the ventilator generates pressure in proportion to the patient’s effort. PAV became commercially available in Europe in 1999 and was approved in the United States in 2006, available on the Puritan Bennett 840 ventilator

111


• Provides pressure, flow assist, and volume assist in proportion to the patient’s spontaneous effort, the greater the patient’s effort, the higher the flow, volume, and pressure• The operator sets the ventilator’s volume and

flow assist at approximately 80% of patient’s elastance and resistance. The ventilator then generates proportional flow and volume assist to augment the patient’s own effort

112

Ventilator settingsin proportional assist ventilation

• Ventilator settings in PAV are:• Airway type (endotracheal tube, tracheostomy)• Airway size (inner diameter)• Percentage of work supported (assist range 5%–95%)• Tidal volume limit• Pressure limit• Expiratory sensitivity (normally, as inspiration• ends, flow should stop; this parameter tells the

ventilator at what flow to end inspiration).

113


• Indications• Patients who have WOB problems

associated with worsening lung characteristics

• Asynchronous patients who are stable and have an inspiratory effort

• Ventilator-dependent patients with COPD

115

How does the clinician know where to set the “%Support”?

The PB 840 has the option of measuring WOB

• Vital signs• ABG• Signs of respiratory distress

– Respiratory rate > 40 breaths/minute PLUS…

– Marked use of accessory muscles

– Diaphoresis– Abdominal paradox– Marked complaint of

dyspnea– Etc…

Sound Clinical Assessment.


• Advantages– The patient controls the ventilatory variables ( I,

PIP, TI, TE, VT)– Trends the changes of ventilatory effort over time– When used with CPAP, inspiratory muscle work is

near that of a normal subject and may decrease or prevent muscle atrophy

– Lowers airway pressure

118

Increase Support

Sedate

The practitioner’s typical response to an increase in demand is what?

Ventilatory Demand

These can lead to disuse atrophy of the respiratory muscles or lowering of the CO2 set point.

Or

• Start patients at 70% and wean back to stabilize• When disease process has sufficiently reversed,

decrease %Support over 2 hr intervals• On average, patients will breathe at 7 mL/kg; some may

want less while others may want more• Some patients have a high rate normally, so a high rate

on PAV+ may or may not reflect distress; check other signs; try increasing assist to see if rate goes down

• Don’t be surprised if respiratory rate climbs when switching from other modes

Management tips from Dr. Magdy Younes, inventor

PAV™+ Software Option Clinical Description

Dr. Younes is the inventor of Proportional Assist/PAV. The tips in this presentation are his suggestions and are not necessarily those of Tyco Healthcare/Puritan Bennett. Proportional Assist and PAV are trademarks of The University of Manitoba and are used under license by Puritan Bennett.


• Disadvantages– Patient must have an adequate spontaneous respiratory drive – Variable VT and/or PIP– Correct determination of CL and Raw is essential (difficult).

Both under and over estimates of CL and Raw during ventilator setup may significantly impair proper patient-ventilator interaction, which may cause excessive assist (“Runaway”) – the pressure output from the ventilator can exceed the pressure needed to overcome the system impedance (CL and Raw)

– Air leak could cause excessive assist or automatic cycling– Trigger effort may increase with auto-PEEP

121

PAV+ is NOT recommended for…

122

Paw

PDI

VT

Flow

0.2 sec/div

PSV

PAV

Review

124

What is it, why do we use it, what do we set and who does it benefit?

-APRV-PRVC-Autoflow-Volume support-Adaptive Support Ventilation-Volume Assured Pressure Support-MMV-PAV-ATC

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Advanced Modes of Mechanical Ventilation

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