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Acute Respiratory Distress Syndrome

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Acute Respiratory Distress Syndrome

  1. 1. ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS) Timothy G. Janz, MD Department of Emergency Medicine Pulmonary/Critical Care Division Department of Internal Medicine
  2. 2. ARDS Definitions <ul><li>Acute Lung Injury </li></ul><ul><ul><li>150 – 200 mmHg < PaO 2 /FIO 2 < 250 – 300 mmHg </li></ul></ul><ul><li>ARDS </li></ul><ul><ul><li>PaO 2 /FIO 2 < 150 – 200 mmHg </li></ul></ul>
  3. 3. ARDS Epidemiology <ul><li>Incidence: </li></ul><ul><ul><li>5 – 71 per 100,000 </li></ul></ul><ul><li>Financial cost: </li></ul><ul><ul><li>$5,000,000,000 per annum </li></ul></ul>
  4. 4. ARDS Pathophysiology <ul><li>Profound inflammatory response </li></ul><ul><li>Diffuse alveolar damage </li></ul><ul><ul><li>acute exudative phase (1-7days) </li></ul></ul><ul><ul><li>proliferative phase (3-10 days) </li></ul></ul><ul><ul><li>chronic/fibrotic phase (> 1-2 weeks) </li></ul></ul>
  5. 5. ARDS Acute Exudative Phase <ul><li>Basement membrane disruption </li></ul><ul><ul><li>Type I pneumocytes destroyed </li></ul></ul><ul><ul><li>Type II pneumocytes preserved </li></ul></ul><ul><li>Surfactant deficiency </li></ul><ul><ul><li>inhibited by fibrin </li></ul></ul><ul><ul><li>decreased type II production </li></ul></ul><ul><li>Microatelectasis/alveolar collapse </li></ul>
  6. 6. ARDS Acute Exudative Phase
  7. 7. ARDS Acute Exudative Phase
  8. 8. ARDS Acute Exudative Phase
  9. 9. ARDS Proliferative Phase <ul><li>Type II pneumocyte </li></ul><ul><ul><li>proliferate </li></ul></ul><ul><ul><li>differentiate into Type I cells </li></ul></ul><ul><ul><li>reline alveolar walls </li></ul></ul><ul><li>Fibroblast proliferation </li></ul><ul><ul><li>interstitial/alveolar fibrosis </li></ul></ul>
  10. 10. ARDS Proliferative Phase
  11. 11. ARDS Fibrotic Phase <ul><li>Characterized by: </li></ul><ul><ul><li>local fibrosis </li></ul></ul><ul><ul><li>vascular obliteration </li></ul></ul><ul><li>Repair process: </li></ul><ul><ul><li>resolution vs fibrosis </li></ul></ul>
  12. 12. ARDS Pathophysiology <ul><li>Interstitial/alveolar edema </li></ul><ul><li>Severe hypoxemia </li></ul><ul><ul><li>due to intra-pulmonary shunt (V/Q = 0) </li></ul></ul><ul><ul><li>shunt ~ 25% - 50% </li></ul></ul><ul><li>Increased airway resistance </li></ul>
  13. 13. ARDS Pathophysiology <ul><li>High ventilatory demands </li></ul><ul><ul><li>high metabolic state </li></ul></ul><ul><ul><li>increased V D /V T </li></ul></ul><ul><ul><li>decreased lung compliance </li></ul></ul><ul><li>Pulmonary HTN </li></ul><ul><ul><li>neurohumoral factors, hypoxia, edema </li></ul></ul>
  14. 14. ARDS Etiology
  15. 15. ARDS Etiology <ul><li>Hospital-acquired </li></ul><ul><ul><li>infection/sepsis </li></ul></ul><ul><ul><li>massive blood transfusions </li></ul></ul><ul><ul><li>gastric aspiration </li></ul></ul><ul><li>Community-acquired </li></ul><ul><ul><li>trauma </li></ul></ul><ul><ul><li>pneumonia </li></ul></ul><ul><ul><li>drugs/aspiration/inhalations </li></ul></ul>
  16. 16. ARDS Clinical Phases <ul><li>I. Injury Phase </li></ul><ul><li>II. Latent/Lag Phase </li></ul><ul><li>III. ARF Phase </li></ul><ul><li>IV. Recuperative/Terminal Phase </li></ul>
  17. 17. ARDS Clinical Features <ul><li>Acute dyspnea/tachypnea </li></ul><ul><ul><li>rales/rhonchi/wheezing </li></ul></ul><ul><li>Resistant hypoxemia </li></ul><ul><ul><li>PaO 2 /FIO 2 < 150 – 200 mmHg </li></ul></ul><ul><li>CXR </li></ul><ul><ul><li>diffuse, bilateral infiltrates </li></ul></ul><ul><li>No evidence of LV failure </li></ul><ul><ul><li>(PAWP < 18 mmHg) </li></ul></ul>
  18. 18. ARDS Clinical Features: CXR
  19. 19. ARDS Clinical Features: CXR
  20. 20. ARDS Differential Diagnosis <ul><li>CARDIOGENIC PULMONARY EDEMA </li></ul><ul><li>Bronchopneumonia </li></ul><ul><li>Hypersensitivity pneumonitis </li></ul><ul><li>Pulmonary hemorrhage </li></ul><ul><li>Acute interstitial pneumonia (Hamman-Rich Syndrome) </li></ul>
  21. 21. ARDS Diagnosis <ul><li>Resistant hypoxemia </li></ul><ul><ul><li>PaO 2 /FIO 2 < 150 – 200 mmHg </li></ul></ul><ul><li>CXR </li></ul><ul><ul><li>diffuse, bilateral infiltrates </li></ul></ul><ul><li>No evidence of LV failure </li></ul><ul><ul><li>(PAWP < 18 mmHg) </li></ul></ul>
  22. 22. ARDS Diagnosis
  23. 23. ARDS Diagnosis <ul><li>Based on clinical criteria </li></ul><ul><ul><li>no diagnostic tests </li></ul></ul><ul><li>Confirmatory tests: </li></ul><ul><ul><li>PA catheter </li></ul></ul><ul><ul><ul><li>PAWP = normal/reduced </li></ul></ul></ul><ul><ul><li>[bronchial secretion protein]:[serum protein] </li></ul></ul><ul><ul><ul><li>ratio > 70% - 80% </li></ul></ul></ul>
  24. 24. ARDS Treatment: Standard <ul><li>Rx underlying cause </li></ul><ul><li>Adequate oxygenation/ventilation </li></ul><ul><ul><li>PaO 2 > 60 mmHg; SaO 2 > 90% </li></ul></ul><ul><li>PEEP usually needed to meet O 2 goals </li></ul><ul><ul><li>Prevents/corrects alveolar collapse </li></ul></ul><ul><ul><li>converts: (V/Q = 0) to V/Q mismatch </li></ul></ul>
  25. 25. ARDS “Open-Lung “ Approach to PEEP Amato , Am J Respir Crit Care Med 1995; 152:1835
  26. 26. ARDS Treatment: PEEP <ul><li>“Open-lung” approach </li></ul><ul><ul><li>Not practical </li></ul></ul><ul><ul><li>Does not improve outcomes </li></ul></ul><ul><li>Optimal PEEP </li></ul><ul><ul><li>??? </li></ul></ul><ul><ul><li>Most cases: PEEP ~ 15 – 20 cmH 2 O </li></ul></ul>
  27. 27. ARDS Optimal PEEP <ul><li>Maximize lung compliance </li></ul><ul><ul><li>Crs = Vt/(P plateau – PEEP) </li></ul></ul><ul><li>Maximize O 2 delivery </li></ul><ul><ul><li>DO 2 = 10 x CO x (1.34 x Hgb x SaO 2 ) </li></ul></ul><ul><li>Lowest PEEP to oxygenate @ FIO 2 < .60 </li></ul><ul><li>Empiric approach: </li></ul><ul><ul><li>PEEP = 16 cmH 2 O and Vt = 6 ml/kg </li></ul></ul>
  28. 28. ARDS Optimal PEEP <ul><li>ARDS Network protocol </li></ul><ul><li>FIO 2 - 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 </li></ul><ul><li>PEEP - 5 5-8 8-10 10 10-14 14 14-18 18-22 </li></ul>ARDS Network, N Engl J Med 2000; 342:1301 www.ardsnet.org
  29. 29. ARDS Ventilator-Induced Lung Injury
  30. 30. ARDS Treatment:Lung-Protective Ventilation ARDS Network, N Engl J Med 2000; 342:1301 ardsnet.org
  31. 31. ARDS Treatment: Lung-Protective Ventilation <ul><li>V T = 6 mL/kg </li></ul><ul><li>Limit plateau pressures < 30 cmH 2 O </li></ul><ul><ul><li>Volume controlled ventilation </li></ul></ul><ul><li>Limit peak airway pressures < 40 cmH 2 O </li></ul><ul><ul><li>Pressure controlled ventilation </li></ul></ul>
  32. 32. ARDS Treatment: Lung-Protective Ventilation <ul><li>V T = 6 mL/kg </li></ul><ul><li>Limit peak airway pressures < 40 cmH 2 O </li></ul><ul><li>Limit plateau pressures < 30 cmH 2 O </li></ul>
  33. 33. ARDS Treatment: Lung-Protective Ventilation <ul><li>Complications: (derecruitement) </li></ul><ul><ul><li>Elevated PaCO 2 </li></ul></ul><ul><ul><ul><li>Limit: pH > 7.20 –7.25 </li></ul></ul></ul><ul><ul><li>Worsening hypoxemia </li></ul></ul><ul><ul><ul><li>Correction: </li></ul></ul></ul><ul><ul><ul><ul><li>Recruitement maneuver </li></ul></ul></ul></ul><ul><ul><ul><ul><li>increasing PEEP </li></ul></ul></ul></ul>
  34. 34. ARDS Treatment: Mechanical Ventilation (MV) <ul><li>Pressure controlled ventilation </li></ul><ul><ul><li>Controlled airway pressures </li></ul></ul><ul><ul><li>Controlled inspiratory times </li></ul></ul><ul><ul><li>Patient comfort </li></ul></ul><ul><li>Effectiveness: </li></ul><ul><ul><li>PCV = VCV </li></ul></ul>
  35. 35. ARDS Treatment: Alternate Modes of MV <ul><li>Inverse-ratio ventilation </li></ul><ul><li>Airway pressure-release ventilation </li></ul><ul><li>Bilevel airway pressure ventilation </li></ul><ul><li>Proportional-assist ventilation </li></ul><ul><li>High-frequency ventilation </li></ul><ul><li>ECMO </li></ul><ul><li>Tracheal gas insufflation </li></ul>
  36. 36. ARDS Treatment: Prone Positioning Chatte, Am J Respir Crit Care Med 1997; 25:1539
  37. 37. ARDS Treatment: Prone Positioning
  38. 38. ARDS Treatment: Prone Positioning <ul><li>65% responders </li></ul><ul><li>Multiple proposed mechanisms </li></ul><ul><ul><li>Improved oxygenation </li></ul></ul><ul><li>Difficult to implement </li></ul><ul><li>No improvement in outcomes </li></ul>
  39. 39. ARDS Treatment: Partial Liquid Ventilation <ul><li>Lungs filled to FRC with perflubron </li></ul><ul><ul><li>17 times more O 2 dissolved than water </li></ul></ul><ul><ul><li>Low surface tension </li></ul></ul><ul><ul><li>Gravitates to dependent areas of lungs </li></ul></ul><ul><li>Nontoxic </li></ul><ul><ul><li>Minimally absorbed </li></ul></ul><ul><ul><li>Eliminated by evaporation </li></ul></ul>
  40. 40. ARDS Treatment: Partial Liquid Ventilation <ul><li>Used as lavage + conventional MV </li></ul><ul><li>Multiple proposed mechanisms </li></ul><ul><ul><li>Improves oxygenation </li></ul></ul><ul><li>No improvement in outcomes </li></ul>
  41. 41. ARDS Treatment: Vasodilators Gerlach, Eur J Clin Invest 1993; 23:499
  42. 42. ARDS Treatment: Vasodilators <ul><li>NO has 83% response rate </li></ul><ul><li>Problems: </li></ul><ul><ul><li>Special equipment </li></ul></ul><ul><ul><li>Rebound phenomenon </li></ul></ul><ul><ul><li>No improvements in outcomes </li></ul></ul><ul><li>Prostacyclin may be better agent </li></ul>
  43. 43. ARDS Treatment: Other Modalities <ul><li>Antiinflammatory agents </li></ul><ul><ul><li>Steroids may have a role </li></ul></ul><ul><li>Antioxidants </li></ul><ul><li>Surfactant replacement </li></ul><ul><li>Increased alveolar fluid removal </li></ul><ul><ul><li>Effect sodium channels </li></ul></ul><ul><ul><li>Activate Na + -K + -ATPase pump </li></ul></ul>
  44. 44. ARDS Prognosis <ul><li>Mortality </li></ul><ul><ul><li>30% - 50% </li></ul></ul><ul><ul><li>Death from respiratory failure = 15% - 18% </li></ul></ul><ul><ul><ul><li>Most common cause of death - sepsis/infection </li></ul></ul></ul><ul><li>Outcomes </li></ul><ul><ul><li>Majority have near-normal lung function </li></ul></ul><ul><ul><ul><li>Small % develop pulmonary fibrosis </li></ul></ul></ul><ul><ul><li>Neuropsychiatric sequelae – may be high </li></ul></ul>
  45. 45. The End

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