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
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
Small V T, PEEP and LPV 9 8 7 6 5 4 3 2 1 Extravascular lung water (ml/kg) 8 7 6 5 4 3 1 HiP-HiV LoP-HiV HiP-LoV I 125 albumin (%) HiP-HiV LoP-HiV HiP-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 1 21 st 22 nd July 11 3
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 Volume Key: a- disconnection b- PEEP c- HFOV d- static inflation e- HFOV at initial Paw Time & Anesth Analg 1982 & J Appl Physiol 1983 High Lung Volume and Oxygenation 48 4 PaO 2 (mmhg) 3 24 16 8 HFO-A/HI HFO-A/LO H PL PSI 1 2 3 4 5 6 7 Time (hours) & McCulloch et al. Am Rev Resp Dis 1988 4
Exploiting Hysteresis to achieve the desired lung volume 21 st 22 nd July 11 The Pressure-Volume Relationship Hysteresis Volume Pressure 5
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 OPT TLC Relative Δ in lung volume CCP UIP LIP MAP cmh 2 O 21 st 22 nd July 11 & Dargaville et al. ICM, 1 6
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 1 & Jonson Intensive Care Med 5 Ventilation along the inflation limb ARM from ZEEP Zero PEEP & Halter et al Am J Respir Crit Care Med 3 21 st 22 nd July 11 7
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 3 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 Alveolar stability can be maintained during expiration along the deflation limb & Albaiceta Crit Care Med 4 Ventilation along the deflation limb Post recruitment PEEP 5 cmh 2 O Post recruitment PEEP 1 cmh 2 O & Halter et al Am J Respir Crit Care Med 3 21 st 22 nd July 11 8
Achieving Ventilation on the Deflation Limb Alveolar Recruitment Techniques 21 st 22 nd July 11 Sustained inflations during HFOV Bond et al: HFOV with SI vs HFOV alone SI of 3 cm H 2 O for 15 s higher oxygenation target in the SI group achieved at the same P aw & Crit Care Med 1993 Walsh et al: systematic examination of magnitude and duration of SI SI of 5 cm H 2 O > P aw or for 3 s were ineffective at improving oxygenation SI of 1 cm H 2 O > P aw for 1 s always effective & J Appl Physiol 1988 9
24 16 12 8 4 24 16 12 8 4 24 16 12 8 4 24 16 12 8 4 1 2 3 4 5 14 15 1 2 3 4 5 6 7 8 14 15 1 2 3 4 5 14 15 1 2 3 14 15 14/4/15 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 P aw 5 cm H 2 O lower if a dynamic inflation was used & J Appl Physiol 1988 Standard Strategy Comparison of Alveolar Recruitment Strategies Standard Strategy Escalating Strategy 24 Remain at target P aw Sustained DI Strategy Repeated DI Strategy P aw (cm H 2 O above CMV P aw ) 16 12 8 4 1 2 3 4 5 14 15 Time (minutes) & Pellicano et al ICM 9 1
Comparison of Alveolar Recruitment Strategies: Lung Volume 4 ΔTGV (expressed as %TLC) 21 st 22 nd July 11 35 3 25 15 1 5 Target P aw 1 5 15 Time (mins post-recruitment) & Pellicano et al ICM 9 Escalating Sustained DI Repeated DI Standard * *p =.4 ANOVA Comparison of Alveolar Recruitment Strategies: Oxygenation & Pellicano et al. ICM 9 11
Comparison of Alveolar Recruitement Strategies: End Lung Volume & Pellicano et al. ICM 9 Comparison of Recruitment Strategies: Homogeneity of lung Volume & Pellicano et al ICM 9 12
The Open Lung Approach To Lung Protection Open Lung Ventilation Lachmann, Van Kaam et al (1992 4) 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 5% of TLC (after SI) & Rimensberger et al Crit Care Med 1999 & Rimensberger et al Intensive Care Med 13
Open Lung Ventilation Short-term outcome & van Kaam et al, Crit Care Med 4 Open Lung Ventilation Lung injury outcome & van Kaam, Ped Research, 3 14
Open Lung Ventilation 1 P max Normalised Volume (%) 8 6 4 - -4-6 P final P initial R 2 =.97 4 6 8 1 Normalised Pressure (%) & Tingay et al Am J Respir Crit Care Med, 6 Open Lung Ventilation Lung volume changes during recruitment Pressure/oxygentation curve Pressure/impedance curve 1 1 SpO 2 /FIO 2 (%) 8 6 4 Impedance (%) 8 6 4 4 6 8 1 Pressure (%) 4 6 8 1 Pressure (%) n=15 GA=28.7 wk BW=97 g & Miedema et al. J of Pediatr 11 15
PV relationship influences lung mechanics & Tingay et al Crit Care Med 13 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 21 st 22 nd July 11 16
Time Dependence of Lung Recruitment Time Dependence Kolton et al: Showed time dependent recruitment in both HFOV and CMV groups & Anesth Analg 1982 Volume Time Key: a- disconnection b- PEEP c HFOV/CMV d static inflation e HFOV/CMV at initial P aw Time 17
Time Dependence 4 ΔTGV (expressed as %TLC) 35 3 25 15 1 5 Target P aw 1 5 15 Time (mins post-recruitment) Escalating Sustained DI Repeated DI Standard * 21 st 22 nd July 11 & Pellicano et al ICM 9 Time dependence during HFV in nrds Stabilization time n=13 GA=26 wk BW=79 g Age= 4 days & Thome et al. AJRCCM 1998 18
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
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 21 st 22 nd July 11 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 6 minutes depending on underlying lung disease 21 st 22 nd July 11