14/04/15

1

What is an Optimal Paw Strategy?

Anastasia Pellicano Neonatologist

Royal Children’s Hospital, Melbourne

A Physiological Rationale

Acute injury sequence

NN Rocourt Lung injury is a multi-factorial event of conflicting aetiologies

Barotrauma Volutrauma Atelectotrauma Biotrauma Oxidative Toxicity Fluid, blood, protein leakage and impaired mechanics

14/04/15

2

Respiratory failure Mechanical ventilation

- Oedema - Inflammation - Surfactant inhibition

Ventilator-induced lung injury

Lung protective ventilaton

Lung Protective Strategies

•  Lung Protective Mechanical Ventilation Strategies aim to:

•  Achieve optimal gas exchange – Recruit collapsed alveoli uniformly – Minimise the known causes of VILI: - Atelectasis - Volutrauma - Sheer-force stresses - Oxidative Injury - Rheotrauma

14/04/15

3

Small VT, PEEP and LPV

& Dreyfuss D et al. Am Rev Resp Dis, 1985

Extravascular lung water (ml/kg)

I125 albumin (%)

0 1 2 3 4 5 6 7 8 9

HiP-HiV LoP-HiV HiP-LoV 0

10 20 30 40 50 60 70 80

HiP-HiV LoP-HiV HiP-LoV

HFOV Workshop 21st – 22nd July 2011

18 trials (n=3229 infants) •  Subgroup analysis revealed it was more

important how ventilation was delivered, rather than modality of ventilation: – Low lung volume strategies: worse outcomes – High lung volume strategies: small but

significant reduction in death or CLD

& Cools et al Lancet 2010

Optimal ventilation strategy - systematic review

14/04/15

4

Effect of a single sustained inflation on lung volume and oxygenation during HFOV

Kolton et al •  During HFOV, a static

inflation (SI) improved lung volume

Hamilton et al 1983 •  During ventilation, a static

inflation improved oxygenation in HFOV group

& J Appl Physiol 1983 & Anesth Analg 1982

Time

Volu

me

Key: a- disconnection b- PEEP

d- static inflation e- HFOV at initial

Paw

c- HFOV

High Lung Volume and Oxygenation

& McCulloch et al. Am Rev Resp Dis 1988

H PL PSI 1 2 3 4 5 6 7

80

160

240

320

400

480

HFO-A/HIHFO-A/LO

Time (hours)

PaO

2 (m

mH

g)

14/04/15

5

HFOV Workshop 21st – 22nd July 2011

Exploiting Hysteresis to achieve the desired lung volume

The Pressure-Volume Relationship Hysteresis

Volu

me

Pressure

14/04/15

6

Targeting Ventilation on the PV Relationship

& Froese AB, Crit Care Med 1997

•  2 injury zones during mechanical ventilation •  Low Lung Volume

Ventilation tears adhesive surfaces

•  High Lung Volume Ventilation over-distends, → Volutrauma

•  Need to find the “Sweet Spot”

HFOV Workshop 21st – 22nd July 2011

Mapping the PV Relationship using an open lung ventilation strategy

LIP

UIP

TLC

CCP

OPT

MAP cmH2O

Rel

ativ

e Δ

in lu

ng v

olum

e

& Dargaville et al. ICM, 2010

14/04/15

7

Ventilation along the inflation limb •  Amato et al proposed ventilation along the inflation limb

between LCP and UCP & N Engl J Med 1998; 338: 347 - 354

•  At alveolar level: –  Gains in lung volume may be either by recruitment of

alveoli, or overdistension of already recruited lung units –  Relative proportion of each varies along the inflation

limb •  Affected by continued recruitment along the whole limb •  At no point along the inflation limb can all mechanical

causes of VILI be minimised & Hickling et al Am J Respir Crit Care Med 2001

& Jonson Intensive Care Med 2005

HFOV Workshop 21st – 22nd July 2011

Ventilation along the inflation limb

ARM from ZEEP

& Halter et al Am J Respir Crit Care Med 2003

Zero PEEP

14/04/15

8

Ventilation along the deflation limb •  Affected by alveolar collapse only at pressures below the

critical closing pressure & Halter et al Am J Respir Crit Care Med 2003

•  Volume loss likely a combination of decreasing alveolar dimensions and derecruitment of lung units

•  Pressure required to open lung units exceeds that required to prevent collapse once opened

& Rimensberger Intensive Care Med 2000

•  Alveolar stability can be maintained during expiration along the deflation limb

& Albaiceta Crit Care Med 2004

HFOV Workshop 21st – 22nd July 2011

Ventilation along the deflation limb

Post recruitment PEEP 10 cmH2O

& Halter et al Am J Respir Crit Care Med 2003

Post recruitment PEEP 5 cmH2O

14/04/15

9

HFOV Workshop 21st – 22nd July 2011

Achieving Ventilation on the Deflation Limb

Alveolar Recruitment Techniques

Sustained inflations during HFOV

•  Walsh et al: –  systematic examination of magnitude and duration of SI –  SI of 5 cm H2O > Paw or for 3 s were ineffective at improving oxygenation –  SI of 10 cm H2O > Paw for 10 s always effective –  & J Appl Physiol 1988

•  Bond et al:

–  HFOV with SI vs HFOV alone –  SI of 30 cm H2O for 15 s –  higher oxygenation target in the SI group achieved at the same Paw & Crit Care Med 1993

14/04/15

10

Sustained inflations during HFOV

•  Byford et al (1988) –  comparison of static and dynamic inflations during

HFOV –  both effective at improving oxygenation and increasing

lung volume –  an equivalent improvement in oxygenation or lung

volume could be achieved at a Paw 5 cm H2O lower if a dynamic inflation was used

& J Appl Physiol 1988

Time (minutes)

P aw (c

m H

2O a

bove

CM

V P

aw)

Standard Strategy

0 1 2 3 4 5 14 150

4

8

12

16

20

24

Remain at target Paw

0 1 2 3 4 5 6 7 8 14 150

4

8

12

16

20

24

0 1 2 3 14 150

4

8

12

16

20

24

Comparison of Alveolar Recruitment Strategies

0 1 2 3 4 5 14 150

4

8

12

16

20

24

0 1 2 3 4 5 14 150

4

8

12

16

20

24

Repeated DI Strategy

Sustained DI Strategy

Escalating Strategy

Standard Strategy

& Pellicano et al ICM 2009

14/04/15

11

HFOV Workshop 21st – 22nd July 2011

0 5

10 15 20 25 30 35 40

1 5 15 Time (mins post-recruitment)

ΔTG

V (e

xpre

ssed

as

%TL

C)

Target Paw

Comparison of Alveolar Recruitment Strategies: Lung Volume

Standard

Repeated DI Sustained DI

Escalating

*p = 0.04 ANOVA

*

& Pellicano et al ICM 2009

Comparison of Alveolar Recruitment Strategies: Oxygenation

& Pellicano et al. ICM 2009

14/04/15

12

Comparison of Alveolar Recruitement Strategies: End Lung

Volume

& Pellicano et al. ICM 2009

Comparison of Recruitment Strategies: Homogeneity of lung

Volume

& Pellicano et al ICM 2009

14/04/15

13

The Open Lung Approach To Lung Protection

Open Lung Ventilation

Ventilation applied with an Open Lung Concept:

1.  Improves Gas exchange 2.  Reduces VILI & protein

leakage 3.  Preserves surfactant function 4.  Attenuates lung mechanics 5.  PPV comparable to HFOV

Small VT PPV (5ml/kg) and HFOV

applied at 50% of TLC (after SI)

& Rimensberger et al Crit Care Med 1999 & Rimensberger et al Intensive Care Med 2000

Lachmann, Van Kaam et al (1992 – 2004) “open the lung, find the closing pressure, re-open it and keep it open!”

14/04/15

14

Open Lung Ventilation Short-term outcome

& van Kaam et al, Crit Care Med 2004

Open Lung Ventilation Lung injury outcome

& van Kaam, Ped Research, 2003

14/04/15

15

Normalised Pressure (%) 0 20 40 60 80 100

Nor

mal

ised

Vol

ume

(%)

0 20 40 60 80

100

Open Lung Ventilation

R2=0.97

Pfinal

-60 -40 -20

Pmax

Pinitial

& Tingay et al Am J Respir Crit Care Med, 2006

Open Lung Ventilation Lung volume changes during recruitment

Pressure/oxygentation curve Pressure/impedance curve

& Miedema et al. J of Pediatr 2011

0 20 40 60 80 1000

20

40

60

80

100

Pressure (%)

SpO

2/FIO

2 (%

)

0 20 40 60 80 1000

20

40

60

80

100

Pressure (%)

Impe

danc

e (%

)

n=15 GA=28.7 wk BW=970 g

14/04/15

16

PV relationship influences lung mechanics

& Tingay et al Crit Care Med 2013

HFOV Workshop 21st – 22nd July 2011

Optimum ventilation strategy

•  Recruits atelectatic lung units •  Maintains ventilation at or near the deflation limb

with pressures above the critical closing pressure and uses the smallest possible amplitudes to effect CO2 removal

•  Is titrated against degree of lung disease, recruitment potential and hysteresis of the lung

•  Is frequently reassessed in response to changes in lung mechanics

14/04/15

17

Time Dependence of Lung Recruitment

Time Dependence

Kolton et al: •  Showed time dependent

recruitment in both HFOV and CMV groups

& Anesth Analg 1982 Time

Time

Volu

me

Key: a- disconnection b- PEEP c – HFOV/CMV d – static inflation e – HFOV/CMV at initial Paw

14/04/15

18

HFOV Workshop 21st – 22nd July 2011

0 5

10 15 20 25 30 35 40

1 5 15 Time (mins post-recruitment)

ΔTG

V (e

xpre

ssed

as

%TL

C)

Target Paw

Time Dependence

Standard

Repeated DI Sustained DI

Escalating

*

& Pellicano et al ICM 2009

Time dependence during HFV in nRDS Stabilization time

& Thome et al. AJRCCM 1998

n=13 GA=26 wk BW=790 g Age= 4 days

14/04/15

19

High-frequency ventilation Stabilization time after recruitment steps •  Dependent on lung condition (surfactant) •  Dependent on distribution of disease •  In early (homogeneous) RDS wait at least 2

minutes and longer depending on response •  In older (heterogeneous) lung disease longer

stabilization times (upto 1 hour) are needed

Conclusions

14/04/15

20

HFOV Workshop 21st – 22nd July 2011

Conclusions

•  High lung volumes are necessary during HFOV

•  Lung volume at a given Paw varies considerably, due to hysteresis

•  Using hysteresis it is possible to ventilate the lung at different points within the pressure-volume relationship, depending on the pressure strategy applied

•  By applying ventilation on the deflation limb, higher lung volumes and better oxygenation can be achieved at a lower Paw

HFOV Workshop 21st – 22nd July 2011

Conclusions •  Alveolar recruitment strategies may be used

upon initiation of HFOV to achieve ventilation near the deflation limb

•  Use stepwise lung recruitment with a stabilization time between 2 – 60 minutes depending on underlying lung disease