Hess, New Modes

Ventilator Modes: What’s New

and What’s Worth Keeping?

An Evidence-Based Approach

Dean Hess PhD RRT

Assistant Director of Respiratory Care

Massachusetts General Hospital

Associate Professor of Anesthesia

Harvard Medical School

Editor in Chief

Respiratory Care

Why New Modes?

� Address important clinical issues:

� poor trigger

� variable physiology

� refractory hypoxemia

� Satisfies our craving for adventure (engineers

and clinicians)

� We like better numbers (seduction by pulse oximetry)

Arguments Against New Modes

� Lack high-level evidence for better patient outcomes

� If we try a new mode and the patient has a good outcome,

we say it was due to the new mode.

� But if try a new mode and there is a bad outcome, we say the

patient was going to die anyway.

� Potential for harm (these are often not reported)

� Improved gas exchange does not necessarily improve

outcomes: high tidal volume, iNO, prone

� New is not necessarily better

� Solution to a problem or in search of a problem?

Mechanical Ventilation Strategies

With Level 1 Evidence For

Improved Outcomes

� Noninvasive ventilation (several meta-analyses)

� Volume/pressure limitation (ARDSnet, Gajic)

� Spontaneous awaking/spontaneous breathing trials (Ely, Kress)

New Modes (Some Not So New)

� Closed loop ventilation

� Negative feedback

� Adaptive pressure control

� Adaptive support ventilation

� Positive feedback

� Proportional assist ventilation

� Tube compensation

� Neurally adjusted ventilatory assist

� SmartCare

� Airway pressure release ventilation

Adaptive Pressure Control:

Negative Feedback Control

� PCV with volume guarantee: AutoFlow, pressure-regulated volume control (PRVC), VC+, adaptive pressure ventilation (APV), volume targeted pressure control, pressure controlled volume guaranteed

� PSV with volume guarantee: Volume Support (VS)

� Pressure adjusts to achieve the target tidal volume: pressure changes with changes in lung mechanics, patient effort, or both

Hess, New Modes

Adaptive Pressure Control:

PRVC, AutoFlow, VC+, APVEffect of compliance increase

(or effort increase)

Branson, Respir Care 2005;50:187Branson, Respir Care 2005;50:187

Effect of compliance decrease(or effort decrease)

The ventilator can take away support if patient effort increases!

Tidal volume limitation is not guaranteed.

1. PRVC: ventilator inspiratory pressure is reduced to the minimum necessary to maintain the airway pressure at 0 cm H2O.

2. AutoFlow and VC+: ventilator inspiratory pressure decreases, but never below a

minimum set by the ventilator algorithm.3. APV: a combination of patterns 1 and 2.

Respir Care 2009;54:1467

Adaptive Support Ventilation:

Negative Feedback Control

� Target minute ventilation: 100 mL/min/kg (IBW)

� % Min Volume: 25 – 350%

� Rate based on Otis minimal work equation (1950)

� All combinations of rate/VT calculated

� Te = 3 RC (I:E ratio)

� PRVC or VS depending upon whether or not the patient is actively breathing

� Available on Hamilton ventilator

Adaptive Support Ventilation

Correct IBW setting importantMay overshoot tidal volumeRole in complicated cases?

apne

a Over-distention (pressure limit)

auto

-PE

EP

rapid-shallow breathing (4.4 mL/kg)

Safety Box↓↓↓↓ P, ↑↑↑↑ rate ↓↓↓↓ P, ↓↓↓↓ rate

↑↑↑↑ P, ↑↑↑↑ rate ↑↑↑↑ P, ↓↓↓↓ rate

Effect of Increased Effort

Jabe

r, A

nest

hesi

olog

y 2

00

9;

11

0:6

20

APC (PRVC)Negative feedback

APC

Proportional Assist Ventilation:

Positive Feedback Control

P = V/C + V R.

(proportion of assist adjustable)

respiratory drive

end-inspiratory and expiratory pause maneuvers of 300 ms every 4 to 10 s to estimate of R and C

With neuromuscular disease, drive may not translate into flow

PAW = V/C + V R.

.WoB=∫P×Vdt

Support adjusted to normalize WoB

Hess, New Modes

Proportional Assist Ventilation

Mar

antz

, JA

P 1

99

6;

80

:39

7

Crit Care Med 2007;35:1048

Tube Compensation:

Positive Feedback Control� Pressure determined by inspiratory effort of the patient

and the resistance of the endotracheal tube

Paw = PEEP + ΔΔΔΔPet

Does not compensate for changes in resistance that occur in-vivo;

e.g., kinking or secretions

Res

pir

Car

e 2

01

0;5

5:5

49

Neurally Adjusted Ventilatory Assistance

(NAVA): Positive Feedback Control

Sinderby, Nature Medicine 1999;5:1433

SmartCare (Draeger Evita XL)� Clinician enters a “Zone of Respiratory Comfort” defined

by breathing frequency, tidal volume and end-tidal PCO2; SmartCare decreases or increases PSV

� SmartCare actively reduces PSV to lowest level set by clinician (e.g., 0 cm H2O); if reached, performs a SBT

Lellouche, AJRCM 2006; 174: 894 Rose, Intensive Care Med 2008;34:1788

Hess, New Modes

Airway Pressure Release

Ventilation (APRV)

Alveolar ventilationOxygenationImproved oxygenation, but is mortality improved?

Transpulmonary pressure with spontaneous breaths?

Airway Pressure-Release

Ventilation (APRV)

� Several names for essentially the same mode: APRV,

BiLevel BIPAP, BiVent, BiPhasic, PCV+, DuoPAP

� Minimizes hazards of high airway pressure??

� Decreased need for sedation??

� Improved ventilation of dependant lung zones?

Froese, Anesthesiology 1974;41:242

Act

a A

naes

thes

iol

Sca

nd 2

00

4;

48

: 7

22

Transpulmonary Pressure: APRV

Neu

man

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nten

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Car

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ed 2

00

2;2

8:1

74

2

The Evidence for New Ventilator

Modes …

It’s not the ventilator mode that makes a difference …

… It’s the skills of the clinician that makes the difference.

Any ventilator mode has the potential to do harm!

High level evidence is lacking that any new ventilator

mode improves patient outcomes compared to existing

lung-protective ventilation strategies.