Proportional Assist Ventilation(PAV+) and WOB

L. Brochard, G Carteaux

Conflicts of interest

• Our clinical research laboratory has received research grantsfor clinical trials from the following companies– Covidien (PAV+)

– Dräger (SmartCare)

– General Electric (FRC)

– Respironics (NIV)

– Fisher Paykel (Optiflow)

– Vygon (CPAP)

ABC of ventilationPSV, PAV, NAVA

Trigger Control Cycling end

expiration

PSV Flow or

Pressure

Constant

Pressure

% Peak-

Flow

PEEP

NAVA patient

EMG

Pressure

proportion-

nal to

EMGdi

End of

EMGdi

PEEP and

EMGdi

PAV Flow or

Pressure

Pressure

proportion-

nal to flow

and volume

End of

Patient

Flow

PEEP

VENTILATEUR

Nerf phrénique

Système nerveux central

Stimulation et contractiondiaphragmatique

Variation de pression

Expansion de la paroi thoracique et des poumons

Variation de débit, de volume

NAVA

Technologie

idéale

Technologie

actuelle

PAV

huge

Paw proportional

RESPIRATORY SYSTEM MODEL

Compliance and Resistance = CONSTANT

Pressure, Volume, Flow= VARIABLES

Equation of Motion

muscle + ventilator

Equation of motion

Pappl = (VxE) + (V'xR)

Pappl = Paw + Pmus

Pappl = (VxE) + (V'xR) = Pel + Pres

Gain

G: gains for volume (VA) and flow (FA)VA is a fraction (percentage) of Ers, and FA is a fraction of Rrs

Estimation of Elastance

300 ms end inspiratory pause manoeuvre at a random intervals of 4 to 10 breaths : PplatPAV

EPAV = (PplatPAV - PEEPtot) / Vt

Younes M, et al. AJRCCM 2001;164:50-60

FLOW

Pes

Paw

GAIN = 40%

Settings in PAV+

FiO2 PEEP Gain

How to adjust it?

understand « Gain »

K =1

1 - Gain

(P0 = 0) Ptot = K . |Pmus|For a Gain of 75% support

K =1

0.25

K =1

1 - 0.75

K = 4

Paw

25% 75%

100%

Ptot

Pmus

Carteaux et al CCM 2013

Pmus,Peak = (Paw,Peak – PEEP) . 1 – Gain

Gain

Delta Paw (cm H20) = Paw,Peak - PEEP

1 2 3 4 5 6 7 8 9 10 12 15 17 20 25 30 35 40

% assist

20 4 8 12 16 20 24 28 32 36 40 48 60 68 80 100 120 140 160

25 3 6 9 12 15 18 21 24 27 30 36 45 51 60 75 90 105 120

30 2 5 7 9 12 14 16 19 21 23 28 35 40 47 58 70 82 93

35 2 4 6 7 9 11 13 15 17 19 22 28 32 37 46 56 65 74

40 2 3 5 6 8 9 11 12 14 15 18 23 26 30 38 45 53 60

45 1 2 4 5 6 7 9 10 11 12 15 18 21 24 31 37 43 49

50 1 2 3 4 5 6 7 8 9 10 12 15 17 20 25 30 35 40

55 1 2 2 3 4 5 6 7 7 8 10 12 14 16 20 25 29 33

60 1 1 2 3 3 4 5 5 6 7 8 10 11 13 17 20 23 27

65 1 1 2 2 3 3 4 4 5 5 6 8 9 11 13 16 19 22

70 0 1 1 2 2 3 3 3 4 4 5 6 7 9 11 13 15 17

75 0 1 1 1 2 2 2 3 3 3 4 5 6 7 8 10 12 13

80 0 1 1 1 1 2 2 2 2 3 3 4 4 5 6 8 9 10

85 0 0 1 1 1 1 1 1 2 2 2 3 3 4 4 5 6 7

90 0 0 0 0 1 1 1 1 1 1 1 2 2 2 3 3 4 4

Pmus,Peak

Gain

()

Carteaux et al CCM 2013

Pmus

RR

Ti Te

Pmus,Peak

PTPmus

Pmus,Peak x Ti

2PTPmus = x RR

CRITERIA FOR WEANING TRIAL

-Resolution of the pathologie requiringintubation-No sign of ARD-Fi02 50%-SaO2 ≥ 90%-Conscious patient-No vasopressor, haemodynamic stability

Adjust FiO2 and PEEP

According to:-Oxygenation (SpO2, PaO2)- Underlying respiratory disease

How to adjust the Gain 1

Standard settings

Assess Pmus

Pmus < 5 cmH2O 5 Pmus 10 cmH2O Pmus > 10 cmH2O

Decrease Gain in steps of 10%

Optimal WOB area.Decrease Gain in steps of 5% while Pmus remains in this area.

Increase Gain in steps of 10%

Initiating PAV+

INITIAL SETTINGS-Gain: 50%-Inspiratory trigger: 1 l/min-Expiratory trigger: 1%-FiO2 et PEEP: no specific rule

ALARMS-Paw max: 40 cmH2O-RR: 40/min-Vte max: 10 ml/kg-Vte min: 0 ml

If appears, while Pmus is in the optimal area

-Signs of ARD-Vte < 5 ml/kg-Respiratory acidosis

Increase Gain in steps of 10%

-Vte > 10 ml/kg-Respiratory alcalosis

Decrease Gain in steps of 10%

FiO2 & PEEP optimisation

2Aditionalsettings

Search another hypertotilation’s cause

Persistance Lack

Regardless of the Gain

Adaptation of the Gain every 8h if needed

Clinical data collected daily

A computer was connected to the

ventilator for continuous recording

of ventilator’s data (sampling frequency =

1 min)

19 switch to ACV

52 PAV+

33 until Extubation

27 settings according to

protocol (82%)

4 needed additional

settings2 out of the

rules

1 Intolerance 18 Aggravation

Carteaux et al CCM 2013

Each box-plot represents a patient

PTPmus median values all over PAV+ ventilation per patientP

TP

mu

s (c

mH

20.s

.min

-1)

Carteaux et al CCM 2013

Conclusions

• Many patients tolerate PAV+ ventilation over several days

• Setting PAV+ to target a « normal » level of effort seems feasible

• The target is reached in 85% of the cases

• Refinement of the Paw criteria may benecessary