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What is an Optimal Paw Strategy?

A Physiological Rationale

Anastasia Pellicano Neonatologist Royal Children’s Hospital, Melbourne

Acute injury sequence

Barotrauma Volutrauma Atelectotrauma Oxidative Toxicity

Fluid, blood, protein leakage and impaired mechanics NN Rocourt Lung injury is a multi-factorial event of conflicting aetiologies

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Respiratory failure

Lung protective ventilaton

Ventilator-induced lung injury

- Oedema - Inflammation - Surfactant inhibition

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

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Small VT, PEEP and LPV

Extravascular lung I125 albumin (%) water (ml/kg) 9 80 8 70 7 60 6 50 5 40 4 30 3 2 20 1 10 0 0 HiP-HiV LoP-HiV HiP-LoV HiP-HiV LoP-HiVHiP-LoV

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

Optimal ventilation strategy - systematic review 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 HFOV Workshop 21st – 22nd July 2011

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

Kolton et al Hamilton et al 1983 • During HFOV, a static • During ventilation, a static inflation (SI) improved inflation improved lung volume oxygenation in HFOV group

Key: a- disconnection b- PEEP c- HFOV d- static inflation e- HFOV at initial

Volume Paw

Time

& Anesth Analg 1982 & J Appl Physiol 1983

High Lung Volume and Oxygenation

480

400

320 HFO-A/HI 240 HFO-A/LO (mmHg) 2

160 PaO

80

H PL PSI 1 2 3 4 5 6 7

Time (hours)

& McCulloch et al. Am Rev Resp Dis 1988

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Exploiting Hysteresis to achieve the desired lung volume

HFOV Workshop 21st – 22nd July 2011

The Pressure-Volume Relationship Hysteresis

Volume

Pressure

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Targeting Ventilation on the PV Relationship

• 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” & Froese AB, Crit Care Med 1997

Mapping the PV Relationship using an open lung ventilation strategy

TLC OPT

CCP UIP in lung volume Δ Relative

LIP

MAP cmH2O

& Dargaville et al. ICM, 2010 HFOV Workshop 21st – 22nd July 2011

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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

Ventilation along the inflation limb

ARM from ZEEP

Zero PEEP

& Halter et al Am J Respir Crit Care Med 2003

HFOV Workshop 21st – 22nd July 2011

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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

Ventilation along the deflation limb

Post recruitment PEEP 5 cmH2O Post recruitment PEEP 10 cmH2O

& Halter et al Am J Respir Crit Care Med 2003

HFOV Workshop 21st – 22nd July 2011

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Achieving Ventilation on the Deflation Limb

Alveolar Recruitment Techniques

HFOV Workshop 21st – 22nd July 2011

Sustained inflations during HFOV

• 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 • 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

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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

Comparison of Alveolar Recruitment Strategies Standard Strategy

24 Standard Strategy

20

16

12 8 24 4

0 0 1 2 3 4 5 14 15 Remain at target Paw Escalating Strategy 20 )

24 aw 20 P 16 16

12

8

4

0 12 0 1 2 3 4 5 6 7 8 14 15 Sustained DI Strategy 8

24 O above CMV CMV O above 20 2 16 4 12

8

4 (cm H (cm 0 0 1 2 3 4 5 14 15 0 aw

Repeated DI Strategy P 0 1 2 3 4 5 14 15

24 20 Time (minutes) 16

12

8 4 & Pellicano et al ICM 2009 0 0 1 2 3 14 15

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Comparison of Alveolar Recruitment Strategies: Lung Volume

40

35 Escalating 30 Sustained DI Repeated DI 25 Standard * 20 15 10 TGV (expressed TGV asΔ %TLC) 5 0 Target 1 5 15 Time (mins post-recruitment) Paw *p = 0.04 ANOVA

& Pellicano et al ICM 2009 HFOV Workshop 21st – 22nd July 2011

Comparison of Alveolar Recruitment Strategies: Oxygenation

& Pellicano et al. ICM 2009

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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

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The Open Lung Approach To Lung Protection

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

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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

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Open Lung Ventilation

Pmax 100

80 60 40 20 0 Pfinal -20 Pinitial Normalised Volume (%) NormalisedVolume -40 R2=0.97 -60 0 20 40 60 80 100 Normalised Pressure (%) & Tingay et al Am J Respir Crit Care Med, 2006

Open Lung Ventilation Lung volume changes during recruitment

Pressure/oxygentation curve Pressure/impedance curve

100 100

80 ) 80 ) % ( %

(

e 2

60 c 60 O n I a F / d 2

40 e 40 O p p m S 20 I 20

0 0 0 20 40 60 80 100 0 20 40 60 80 100 Pressure (%) Pressure (%)

n=15 GA=28.7 wk BW=970 g

& Miedema et al. J of Pediatr 2011

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PV relationship influences lung mechanics

& Tingay et al Crit Care Med 2013

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

HFOV Workshop 21st – 22nd July 2011

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Time Dependence of Lung Recruitment

Time Dependence

Kolton et al: • Showed time dependent recruitment in both HFOV Key: and CMV groups Time a- disconnection & Anesth Analg 1982 b- PEEP c – HFOV/CMV d – static inflation

e – HFOV/CMV at initial P aw Volume

Time

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Time Dependence

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35 Escalating 30 Sustained DI Repeated DI 25 * 20 Standard 15 10 TGV (expressed TGV asΔ %TLC) 5 0 Target 1 5 15 Time (mins post-recruitment) Paw

& Pellicano et al ICM 2009 HFOV Workshop 21st – 22nd July 2011

Time dependence during HFV in nRDS Stabilization time

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

& Thome et al. AJRCCM 1998

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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

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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

HFOV Workshop 21st – 22nd July 2011

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