Minimizing Impact of Ventilation - Critical Care …Cunningham et al. Handbook of Physiology. The...

Proportional assist

D. Georgopoulos, Professor of Medicine,

Department of Intensive Care Medicine,

University Hospital of Heraklion,

University of Crete, Greece

Minimizing Impact

of Ventilation

Conflict of interest

Research grant – Lecture fee

Medtronic

Draeger

Maquet

Pmus = ΔVxErs + V’xRrs

Pel(elastic pressure)

Pres(resistive pressure)

Equation of motion

Spontaneous breathing

Pmuspeak/breath (% of maximum pressure)

Tid

al v

olu

me

Normal constant mechanics (Ers, Rrs)

and normal muscles

Ers, Rrs

Max. Pmus

The patient needs more and more pressure (% of maximum)

to achieve an adequate tidal volumeYounes M. Semin. Respir. Med. 1993; 14:229

PmusI

V’I

Pres=V’I x Rrs

Pel = ΔV x Ers

ΔV

Paw

Paw+Pmus = ΔVxErs + V’xRrs

Equation of motion

Mechanical ventilation

Pel(elastic pressure)

Pres(resistive pressure)

Total pressure

Common Modes of assisted

mechanical ventilation

• Assist volume control

(VT constant)

• Pressure support or pressure assist

(Pressure constant)

Paw + Pmus = V’xRs + VxErs

Equation of motion


Assist Volume control

Independent variablesDependent variable

Peak Effort/breath (% of max)

Tid

al v

olu

me

VT

Volume control decreases the slope

of VT/effort per breath relationship to zero

Let’s place the patient on Volume control

Younes M. Semin. Respir. Med. 1993; 14:229


Equation of motion


Pressure assist/support

Independent variable


Equation of motion


Pressure assist/support

Independent variableDependent variables

Tid

al v

olu

me

PS

Increasing pressure support increases the minimum VT (VTmin)

without affecting the slope of VT/effort per breath relationship

VTmin ≈ PS/Ers

VTmin = VT that the patient receives when he/she relaxes all

inspiratory muscles immediately after triggering

Let’s place the patient on Pressure assist/support


Parallel

upward

shift

Younes M. Semin. Respir. Med. 1993; 14:229

Take home message

The ability of patient to modulate VT either

is cancelled (volume control)

Take home message

The ability of patient to modulate VT either

is cancelled (volume control)

or

is limited exclusively by the disease

(pressure assist/support)

The patient in order to modulate minute ventilation

should change respiratory rate

Several studies have shown that particularly if VT satisfies

patient’s demands, the patient changes minute ventilation by

changing effort per breath (inefficient strategy) and not

breathing frequencyGeorgopoulos et al. Am J Respir Crit Care Med 1997;156:14

Xirouchaki et al. Eur. Respir J 1999;14:508

Meric et al. Respir Physiol and Neurobiology 2014;195:11

Pressure support or volume control

(and any combination between them):

The ventilator drives the patient


Equation of motion


Proportional assist

Dependent variablesDependent variable

Positive feedback (proportionality Paw/Pmus)

Proportional assist

Neither pressure nor volume are controlled

Proportional assist

The patient drives the ventilator

Younes Am Rev Respir Dis 1992;145:114

Younes et al. Am. J. Respir Crit Care Med 2001

Paw = % support x (Pres + Pel)

PAV+

Instantaneous flow and volume drive

the ventilator, while Ers and Rrs are

measured semi-continuously.

Flow is used both for triggering and

cycling off

NAVA

Electrical activity of the diaphragm

drives the ventilator and this signal is

used both for triggering and cycling off

Sinderby Nature Medicine 1999; 5:1433

Sinderby Principles and Practice of Mechanical

Ventilation (ed. Tobin) 3rd edition

assist

Minimum VT is always ZERO

Proportional assist increases the slope of VT/effort per breath relationship

Let’s place the patient on Proportional assist (PAV+ or NAVA)


Tid

al v

olu

me

The patient controls the tidal volume and duration of mechanical inflation

Meza et al. J Appl Physiol 1998;85:1928 Sinderby Nature Medicine 1999; 5:1433

Proportional assist

• Effectiveness of feedback mechanisms (chemical

and reflex) of control of breathing system

• Patient-ventilator synchrony

mismatch in cycling/unmet ventilator demands

periodic breathing (apneas)

• Respiratory muscles function

Chemical – Reflex Feedback: Safeguards

Chemical feedback

Prevents derangement in arterial blood gassesand acid-base balance(hypoxia, hypercapnia,

hypocapnia)

Reflex feedback

Mainly prevents over-distention (Hering-Breuer reflex)

VV

Pmus

ChemicalReflex

Polacheck et al. J Appl Physiol 1980;49:609

Cunningham et al. Handbook of Physiology. The Respiratorysystem. Vol. 2. 1986; pp. 475–528.

Independent on assist level: RR constant on both modes

VT increased ≈ 500 ml VT constant

PtCO2 decreased

by ≈ 10 mmHg

(severe hypocapnia)

PtCO2 constant

Meric et al. Respir Physiol Neurobiology 2014;195:11

PS NAVAFight between

patient and

ventilator mode

(VTmin ≈ PS/Ers)

IneffectiveEffective

Giannouli et al. Am J Respir Crit Care Med 1999

Chemical feedback

Min. Max.

assist

PS

PAV

Critically ill patients

Chemical – Reflex feedback: Safeguards

Chemical feedback

Prevents derangement in arterial blood gassesand acid-base balance(hypoxia, hypercapnia,

hypocapnia)

Reflex feedback

Mainly prevents over-distention (Hering-Breuer reflex)

VV

Pmus

ChemicalReflex

Polacheck et al. J Appl Physiol 1980;49:609

Cunningham et al. Handbook of Physiology. The Respiratorysystem. Vol. 2. 1986; pp. 475–528.

Paw

EAdi

Volume

Pes

↑↑ assist No assist(for one breath)

ChemicalReflex

Grasselli et al. Intensive Care Med 2012;38:1224

Rabbits ventilated with NAVA

The decrease in neural inspiratory time (Hering-Breuer) protects the lung from high VT as a result of high assist

Obviously with other modes the operation of Hering-Breuer reflex is not effective

Data supporting the hypothesis that

control of breathing system (i.e.

feedback mechanisms -brain) may

protect the lung from the ventilator

With proportional assist chemical and reflex feedback mechanisms are effective

Animal dataAllowing animals with acute lung injury to

“control” their ventilatory pattern

(using NAVA) is at least as protective (and

probably more) to the lungs and to non-

pulmonary organs as a low VT strategy

(i.e. protective strategy)

Brander et al. Intensive Care Med. 2009;35:1979

Mirabella et al. Crit Care 2014;18:R22

Anesthesiology 2015

In 12 patients with ARDS

increasing freedom to control

the ventilator (NAVA) maintains

lung-protective ventilation

Human brain

2016 Mar 17;228:69-75

Main results:

Critically ill patients ventilated with PAV+ control the

driving pressure to low levels [10 cmH20 (8-12),

median (IQR)] bybsizing VT to individual respiratory

system compliance using appropriate feedback

mechanisms aimed at limiting the degree of lung stress

108 critically ill patients were placed on PAV+ after at

least 36 hour on CMV and followed for a maximum of

48 hrs

Human brain

Amato MB et al. N Engl J Med 2015;372:747-755.The patients’ control of

breathing system is adept

at protecting the lungs by

preventing high driving

pressure, while not

unnecessarily restricting

tidal volume when this

has no protective value.

Georgopoulos et al. Respir Physiol Neurobiol 2016

17;228:69

ChemicalReflex

Provided that:

Load-independent high respiratory drive that

may override the protective mechanisms, IS

NOT AN ISSUE!

Patients selection is crucial (be very

careful in patients with severe metabolic

acidosis, delirium, ongoing sepsis, high

fever)

With proportional modes:

These feedback mechanisms

are safeguards

Doorduin et al. Am J Respir Crit Care Med 2016

Brochard et al. Am J Respir Crit Care Med. 2016

Toshiba et al. Am J. Respir Crit Care Med 2016

Avoid to use proportional assist when drive

remains high despite the high level of assist

Proportional assist







Normal mechanics (Ers, Rrs)

assist


Let’s place the patient on Proportional assist


Tid

al v

olu

me

The patient controls tidal volume and duration of mechanical inflation

Synchrony = Proportionality

FACT:The proportional modes (NAVA and PAV) promote

patient-ventilator synchronyand tidal volume variability

Non-synchrony may be associated with

prolonged duration of MV and ICU stay and

increased mortality

Thille et al. Intensive Care Med 2006; 32:1515

de Wit et al. J Crit Care 2009; 24:74–80

Blanch et al. Intensive Care Med 2015; 41:633

Vaporidi et al. Intensive Care Med 2017; 43:184

Correcting non-synchrony and outcome?

Giannouli et al. Am J Respir Crit Care Med 1999Kondili et al. Intensive Care Med 2006Xirouchaki et al. Intensive Care Med 2008Costa et al. Intensive Care Med 2011Colombo et al. Intensive Care Med 2008Alexopoulou et al. Intensive Care Med 2013Meric et al. Respir Physiol Neurobiol 2014 Doorduin et al. Crit Care. 2014Spahija et al. Critical Care Medicine 2010Vaschetto et al. Critical Med 2014Terzi et al. Crit Care Med 2010Akoumianaki et al. Respir Physiol Neurobiol 2014Schmidt et al. Crit Care. 2015Doorduin et al. Anesthesiology 2015Carteaux et al. Crit Care Med 2016Demoule et al. Intensive Care Med 2016 Di mussi et al. Crit Care 2016Longhini et al. Crit Care 2017

Proportional assist







Tid

al v

olu

me

PS



VTmin ≈ PS/Ers

Let’s place the patient on Pressure support


Parallel

upward

shift

Tid

al v

olu

me

PS



VTmin ≈ PS/Ers

Let’s place the patient on Pressure support


Parallel

upward

shift

PaCO2 is

decreased

Meza et al. J Appl Physiol 1998;85:1928

0 3 6

8

Paw

Paw

Apnea Apnea Apnea

Sleep quality is poor

characterized by

severe sleep

fragmentation and low

levels of deep sleep

(REM and N3)

Micro-arousals

Stable Stable Stable

Pressure support during sleep

assist



Tid

al v

olu

me


assist



Tid

al v

olu

me


Even at high assist PaCO2 changes minimally

Delisle, S. et al. Respir Care 2013;58:745-753

Apnea index: 0 events/hours 10.5 ±11 events/hour

Apnea

Delisle, S. et al. Annals of Intensive Care 2011;1:4

Compared to PS, NAVA is associated with better sleep architecture

less light sleep

more REM and N3 (deep sleep)

Proportional assist







Carteaux et al. Crit Care Med 2016

With assisted modes of support the diaphragm may become lazy!

With high PS the patient relaxes the

diaphragm immediately after triggering

12–18 hrs of PSV (with PS level that

caused diaphragmatic relaxation after

triggering) resulted in diaphragmatic

atrophy and contractile dysfunction

Hudson et al. Critical Care Medicine 2012

In critically ill patients, there is a linear relationship

between the level of PS and diaphragmatic

atrophy rate (Zambon et al. Crit Care Med 2016)

With Proportional assist the risk of atrophy

should be low

The patient drives the ventilator

Carteaux et al. Crit Care Med 2016

Low PS High PS Low NAVA High NAVA

Di mussi et al. Crit Care 2016

Neuro-ventilator efficiency

(VT/EaDi)

Neuro-muscular efficiency

(Pmus/EaDi)

Over-assist with PS

NAVA

PS


Tid

al v

olu

me

VT

Volume control decreases the slope

of VT/effort per breath relationship to zero

Let’s place the patient on Volume control

Tid

al v

olu

me

PS



VTmin ≈ PS/Ers

VTmin = VT that the patient receives when he/she relaxes all

inspiratory muscles immediately after triggering

Let’s place the patient on Pressure assist/support


Parallel

upward

shift

Normal mechanics (Ers, Rrs)

assist




Tid

al v

olu

me

The patient controls tidal volume and duration of mechanical inflation

Level of assist = strength of the muscle

Take home message

With proportional modes the ventilator is a

powerful inspiratory muscle that obeys the

patient’s control of breathing system

0

10

20

30

40

50

0 10 20 30 40 50

0

10

20

30

40

50

0 10 20 30 40 50

Patients breathing frequency (breaths/min)

Ven

tila

tor

rate

(cy

cles

/min

)

PS (696 measurements) PAV+ (744 measurements)

Xirouchaki et al. Intensive Care Med 2008

Compared to PS, PAV+ reduces ineffective efforts by 77%

Akoumianaki et al. Annals of Intensive Care 2017;7:64

In critically ill patients PAV+ and NAVA are associated

with a better work efficiency than PSV

-13

-11

-9

-7

-5

-3

-1

1

3

5

7

9

11

4 6 8 10 12 14 16 18 20 22

Chan

ge

in Δ

P (

cmH

2O

)

ΔP

PA

V+

-Δ

PC

MV

ΔP during CMV (cmH2O)

87% (58/67)

91% (59/65)

Georgopoulos et al. Respir Physiol Neurobiology 2016 Mar 17;228:69-75

When the lung protective strategy results in high driving pressure (≥15 cmH2O), the patients’ control of

breathing system decreased the driving pressure in the majority (87%) of measurements.

When the lung protective strategy results in low driving pressure (<8 cmH2O), the patients’ control of

breathing system increased the driving pressure in the majority (91%) of measurements.

2Vaschetto et al. Critical Care Medicine. 42(1):74-82, January 2014.

Compared to PS, NAVA eliminates ineffective triggering

Effort response to load

with PAV+ and PS

% d

iffe

ren

ce f

rom

baselin

e

**

* *

0

50

100

150

200

250

ΔPdi ΔPTP/b ΔPTP/min ΔPTP/L

PAV+

PS

Kondili et al. Intensive Care Med 2006; 32:692

With PAV+ the increased demands are met with less effort

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