Mechanical Ventilation in Special Conditions

1. Mechanical Ventilation inSpecial Conditions Dr. Alireza Sedaghat MD - FCCM

2. MV in Special Conditions • ARDS • COPD • Head injury • Neuromuscular disorders

3. Mechanical Ventilation in ARDS

4. ARDS

5. ARDS

6. Definitions • The 1994 North American-European Consensus Conference (NAECC) criteria: • Onset- Acute and persistent • Radiographic criteria- Bilateral pulmonary infiltrates consistent with the presence of edema • Oxygenation criteria - Impaired oxygenation regardless of the PEEP concentration, with a Pao2/Fio2 ratio  300 for ALI and  200 for ARDS • Exclusion criteria- Clinical evidence of left atrial hypertension or PAOP  18 mm Hg. Bernard GR et al., Am J Respir Crit Care Med 1994

7. Old Definitions of ARDS ALI (Acute Lung Injury) • Acute onset • PaO2/FiO2 ratio <300 mmHg • Bilateral infiltrates consistent with pulmonary edema • Absence of left heart failure (PCWP < 15 mm Hg) ARDS • Acute onset • PaO2/FiO2 ratio <200 mmHg • ALI + DAD (Diffuse Alveolar Damage) = ARDS Bernard, GR, et al. Am J Respir Crit Care Med 1994; 149: 818-824.

8. Berlin Definition Acute Onset • Within 7 days of a defined event • Most occur within 72 hours Bilateral Pulmonary Infiltrates • Consistent with pulmonary edema Acute Respiratory Failure • Not fully explained by cardiac failure / fluid overload • No need to exclude heart failure • High PCWP or known CHF can still have ARDS The ARDS Definition Task Force. Acute Respiratory Distress Syndrome. The Berlin Definition. JAMA online May 21, 2012.

9. Berlin Definition • Mild ARDS • PaO2/FiO2 ratio: 200-300 • Previously Acute Lung Injury (ALI) • 27% mortality • Moderate ARDS • PaO2/FiO2 ratio: 100-200 • 32% mortality • Severe ARDS • PaO2/FiO2 ratio: <100 • 45% mortality The ARDS Definition Task Force. Acute Respiratory Distress Syndrome. The Berlin Definition. JAMA online May 21, 2012.

10. Clinical Disorders Associated with theDevelopment of ALI/ARDS Indirect insult Common Sepsis Severe trauma Shock Less common Acute pancreatitis Cardiopulmonary bypass Transfusion-related TRALI Disseminated intravascular coagulation Burns Head injury Drug overdose Direct insult Common Aspiration pneumonia Pneumonia Less common Inhalation injury Pulmonary contusions Fat emboli Near drowning Reperfusion injury Atabai K, Matthay MA. Thorax. 2000. Frutos-Vivar F, et al. Curr Opin Crit Care. 2004.

11. NIH-NHLBI ARDS Network Cause of Lung Injury NHLBI ARDS Clinical Trials Network. N Engl J Med. 2004.

13. Mortality • ARDS mortality rates : 31% to 74% • The main causes of death are non-respiratory causes • Respiratory failure has been reported as the cause of death in 9% to 16% of patients with ARDS. • There is a controversy about the role of hypoxemia as a prognostic factor in adults. Early deaths (within 72 hours) are caused by the underlying illness or injury, whereas late deaths are caused by sepsis or MODS. Frutos-Vivar F, et al. Curr Opin Crit Care. 2004. Vincent JL, et al. Crit Care Med. 2003.

14. Exudative Phase • Rapid onset • Hypoxemia refractory to supplemental oxygen • CXR similar to pulmonary edema • CT Scan: Alveolar filling, consolidation and atelectasis in the dependent lung zones • Pathologic findings: • diffuse alveolar damage with capillary injury and disruption of the alveolar epithelium • hyaline membranes • protein rich fluid edema with neutrophils and macrophages

15. Exudative Phase

16. Fibroproliferative phase • The process may start as early as 5-7 days • The alveolar space becomes filled with mesenchymal cells and their products as well as new blood vessels Some patients progress to fibrosing alveolitis with persistent hypoxemia, increase alveolar dead space and further decrease in pulmonary compliance

17. Fibroproliferative phase • Pulmonary HTN may lead or worsen RV dysfunction • CXR shows linear opacities. • PTX and bullae are common • Histologically, there is fibrosis and partial resolution of the pulmonary edema Mortality is 80% if this phase persists

18. Fibroproliferative phase

29. ARDS: Physiological Abnormalities • Normal airway resistance • Low lung compliance • Decreased time constant t (t= compliance X resistance, complete passive exhalation requires 3-4 t; normally t is about 0.5 s) • Severe shunting process ARDS : Inhomogeneous Consolidation and Atlectasis Radiopathology

30. PIP Plateau Airway Resistance Normal Patient ARDS: Pressure/Time Curve Inspiration Pressure (cm H2O) Time (sec) Expiration

31. Normal Patient ARDS: Volume/Time Curve Inspiration Volume (cm H2O) Time (sec) Expiration

32. Volume (mL) Pressure (cm H2O) ARDS: Low Lung Compliance Expiration Inspiration Deflection point Low Compliance

33. ARDS: Shunting Process

35. Shunt vs Dead Space

36. Indication for MV in patients with ARDS • Increased work of breathing • Oxygenation impairment • Impending ventilatory failure • Acute ventilatory failure

37. ARDS: MV Objectives • Adequate oxygenation: high FiO2 and PEEP with PaO2 targets: lung Protective strategy: lower tidal volumes 4-6 mL/kg to provide lower alveolar pressures <30 cm H2O and avoid barotrauma and volutrauma • Mild ARDS > 70 mm Hg • Moderate ARDS > 60 mm Hg • Severe ARDS > 50 mm Hg

38. Open Lung Approach Pressure-controlled ventilation Maintaining low plateau pressure while monitoring tidal volume Use of recruitment maneuvers Maximize alveolar recruitment with high level of PEEP ARDSnet Approach Maintaining low tidal volume while monitoring plateau pressure Set PEEP based upon FiO2 requirement ARDS: MV Objectives

39. Reduce Ventilator-induced Lung Injury • End –inspiratory plateau pressure < 30 cm H2O to prevent over-distension • Appropriate level of PEEP is maintained to avoid the shear stress of repeatedly opening and closing unstable lung units

41. ARDSNet Approach

42. ARDS network study Prospective, randomized, multicenter study to compare the effectiveness of 2 tidal volumes in patients with ALI and ARDS- 12 ml/kg and 6 ml/kg • 429 subjects randomized to 12 ml/kg of IBW • Airway plateau pressure < 50 cm H2O • 432 subjects randomized to 6 ml/kg of IBW • Airway plateau pressure < 30 cm H2O

43. NIH ARDS Network TrialMechanical Ventilation in ARDS 31% mortality 40% mortality

44. FiO2 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7 0.7 0.8 0.9 0.9 0.9 1.0 PEEP 5 5 8 8 10 10 10 12 14 14 14 16 18 20-24 ARTERIAL OXYGENATION GOAL: PaO2 55-80 mm Hg or SpO2 88-95% Use these FiO2/PEEP combinations to achieve oxygenation goal.

45. CMV (A/C), VCV, Vt 8 mL/kg, then 7 mL/kg after 1 hr, then 6 mL/kg after next 1 hr, increase inspiratory rate to maintain minute ventilation, I:E ratio 1:2, PEEP and FiO2 per FiO2/PEEP table Pplat < 30 cm H2O VT 5 mL/kg ↑ VT by 1 mL/kg VT 4 mL/kg yes yes yes Pplat < 25 cm H2O VT <6 mL/kg yes ↑ VT to 7-8 mL/kg Severe dyspnea no PaO2 55-80 SpO2 88-95 Adjust FiO2 or PEEP Per FiO2/PEEP table no yes FiO2 ≤ 0.4 PEEP= 8 pH < 7.15 ↑ rate Consider HCO3 ↑ VT pH yes no ↓ rate no 7.30-7.45 yes ↑ rate Evaluate for weaning ARDSnet Approach Start Calculate predicted body weight no no yes <7.30 >7.45

48. Open Lung Approach Recruitment Maneuver

49. Recruitment Maneuver • Recruitment Maneuver is: A procedure where a sustained positive pressure is applied, to an injured lung, over an increment of time, to recruit, open and keep open closed alveoli. • Recruitment maneuvers are performed to: Help improve oxygenation, help improve distribution of ventilation, Help improve shunts.

50. Recruitment Maneuver Patient Selection • Primarily on patients with ARDS • Patients in early phase ARDS, before the onset of fibro-proliferation. • Also in non-ARDS patients: • Patients with Alveolar Collapse. • Patients with consistent Atelectasis.