14/04/15 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 1 14/04/15 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 2 14/04/15 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 20 2 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 3 14/04/15 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 4 14/04/15 Exploiting Hysteresis to achieve the desired lung volume HFOV Workshop 21st – 22nd July 2011 The Pressure-Volume Relationship Hysteresis Volume Pressure 5 14/04/15 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 inlung volume Δ Relative LIP MAP cmH2O & Dargaville et al. ICM, 2010 HFOV Workshop 21st – 22nd July 2011 6 14/04/15 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 7 14/04/15 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 8 14/04/15 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 9 14/04/15 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 O above CMV 20 2 16 4 12 8 4 (cm H 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 10 14/04/15 Comparison of Alveolar Recruitment Strategies: Lung Volume 40 35 Escalating 30 Sustained DI Repeated DI 25 Standard * 20 15 10 TGV (expressed as %TLC) Δ 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 11 14/04/15 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 12 14/04/15 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 13 14/04/15 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 14/04/15 Open Lung Ventilation Pmax 100 80 60 40 20 0 Pfinal -20 Pinitial Normalised Volume (%) Normalised Volume -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 15 14/04/15 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 16 14/04/15 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 Paw Volume Time 17 14/04/15 Time Dependence 40 35 Escalating 30 Sustained DI Repeated DI 25 Standard* 20 15 10 TGV (expressed as %TLC) Δ 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 18 14/04/15 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 19 14/04/15 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 20 .