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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 Biotrauma 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 Mechanical ventilation
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
40
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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