1. Acute Lung Injury and ARDS Dalhousie Critical Care Lecture Series

7. Ventilatory-based Strategies in the Management of ARDS/ALI

8. Positive-pressure Mechanical Ventilation Currently, the only therapy that has been proven to be effective at reducing mortality in ALI/ARDS in a large, randomized, multi-center, controlled trial is a protective ventilatory strategy. Tidal volume and plateau pressure

10. Gas Extravasation Barotrauma

11. Recognized Mechanisms of Airspace Injury “ Stretch” “ Shear” Airway Trauma

13. Tension Cysts

15. Links Between VILI and MSOF Biotrauma and Mediator De-compartmentalization Slutsky, Chest 116(1):9S-16S

16. End-Expiration Tidal Forces (Transpulmonary and Microvascular Pressures) Extreme Stress/Strain Moderate Stress/Strain Mechano signaling via integrins, cytoskeleton, ion channels inflammatory cascade Cellular Infiltration and Inflammation Rupture Signaling Marini / Gattinoni CCM 2004 Pathways to VILI

18. Diseased Lungs Do Not Fully Collapse, Despite Tension Pneumothorax … and They cannot always be fully “opened” Dimensions of a fully Collapsed Normal Lung

23. Median Organ Failure Free Days * * * * = 6 ml/kg = 12 ml/kg

28. How Much Collapse Is Dangerous Depends on the Plateau R = 100% 20 60 100 Pressure [cmH 2 O] 20 40 60 Total Lung Capacity [%] R = 22% R = 81% R = 93% 0 0 R = 0% R = 59% From Pelosi et al AJRCCM 2001 Some potentially recruitable units open only at high pressure More Extensive Collapse But Lower P PLAT Less Extensive Collapse But Greater P PLAT

30. Hemodynamic Effects of Lung Inflation With Low Lung Compliance, High Levels of PEEP are Generally Well Tolerated.

31. Effect of lung expansion on pulmonary vasculature . Capillaries that are embedded in the alveolar walls undergo compression even as interstitial vessels dilate. The net result is usually an increase in pulmonary vascular resistance, unless recruitment of collapsed units occurs.

34. Recruitment Parallels Volume As A Function of Airway Pressure Recruitment and Inflation (%) Frequency Distribution of Opening Pressures (%) Airway Pressure (cmH2O)

35. % Opening and Closing Pressures in ARDS 50 High pressures may be needed to open some lung units, but once open, many units stay open at lower pressure. Paw [cmH 2 O] 0 5 10 15 20 25 30 35 40 45 50 0 10 20 30 40 Opening pressure Closing pressure From Crotti et al AJRCCM 2001.

36. Rimensberger ICM 2000 VOLUME (% TLC) Benefit from a recruiting maneuver is usually transient if PEEP remains unchanged afterward.

37. Respiratory Pressure/Volume (P/V) Curve Healthy subject In normal healthy volunteers, the P/V curve explore the mechanical properties of the respiratory system (lung + chest wall) ARDS RV, Residual volume; FRC, Functional residual capacity; TLC, Total lung capacity; UIP, Upper inflection point; LIP, Lower inflection point. The critical opening pressure above which most of the collapsed units open up and may be recruited - CLIN Compliance of the intermediate, linear segment of the P/V curve Maggiore SS, et al. Eur Respir J. 2003. Rouby JJ, et al. Eur Respir J. 2003.

50. Prone Positioning Relieves Lung Compression by the Heart Supine Prone

54. Effect of Prone Positioning on the Survival of Patients with Acute Respiratory Failure Gattinoni L, et al. N Engl J Med. 2001. Kaplan-Meier estimates of survival at six months

58. Conclusions Positive pressure ventilation may injure the lung via several different mechanisms VILI Search for ventilatory “lung protective” strategies Alveolar distension “ VOLUTRAUMA” Repeated closing and opening of collapsed alveolar units “ ATELECTRAUMA” Oxygen toxicity Lung inflammation “ BIOTRAUMA” Multiple organ dysfunction syndrome