1. John J. Marini Alain F. Broccard University of Minnesota Regions Hospital Minneapolis / St. Paul USA Advanced Mechanical Ventilation

4. Partitioning of Alveolar Pressure is a Function of Lung and Chest Wall Compliances Lungs are smaller and pleural pressures are higher when the chest wall is stiff.

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

7. 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.

9. Gas Extravasation Barotrauma

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

11. Tension Cysts

12. Tidally Phasic Systemic Gas Embolism End-Expiration End-Inspiration

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

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

17. Microvascular Fracture in ARDS A Portal for Gas & Bacteria? Hotchkiss et al Crit Care Med 2002; 1 

19. Spectrum of Regional Opening Pressures (Supine Position) Superimposed Pressure ( from Gattinoni ) Lung Units at Risk for Tidal Opening & Closure = Inflated 0 Alveolar Collapse (Reabsorption) 20-60 cmH 2 O Small Airway Collapse 10-20 cmH 2 O Consolidation  Opening Pressure

20. Different lung regions may be overstretched or underinflated, even as measures of total lung mechanics appear within normal limits. Alveolar Pressure Lung Volume UPPER LUNG TOTAL LUNG LOWER LUNG

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

22. % 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.

23. Zone of ↑ Risk

24. Dependent to Non-dependent Progression of Injury

25. Histopathology of VILI Belperio et al, J Clin Invest Dec 2002; 110(11):1703-1716

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

27. Airway Orientation in Supine Position

29. Prone Positioning Evens The Distribution of Pleural & Transpulmonary Pressures

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

31. Proning May Benefit the Most Seriously Ill ARDS Subset SAPS II Mortality Rate > 49 40- 49 31- 40 0 - 31 0.0 0.1 0.2 0.3 0.4 0.5 Quartiles of SAPS II Supine * p<0.05 vs Supine Prone *

32. Proning Helped Most in High V T Subgroup At Risk For VILI V T /Kg < 8.2 8.2- 9.7 9.7- 12 > 12 0.0 0.1 0.2 0.3 0.4 0.5 Mortality Rate Quartiles of V T /Predicted body weight Supine * p<0.05 vs Supine Prone *

33. 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

35. Theoretical Effect of Sustained Inflation on Tidal Cycling Rimensberger ICM 2000 VOLUME (% TLC) Benefit from a recruiting maneuver is usually transient if PEEP remains unchanged afterward.

36. Three Types of Recruitment Maneuvers S-C Lim, et al Crit Care Med 2004

39. Auto-PEEP Adds To the Breathing Workload The pressure-volume areas correspond to the inspiratory mechanical workloads of auto-PEEP (AP) flow resistance and tidal elastance.

42. Volume Losses in Recumbent Positions Note that COPD patients lose much less lung volume than normals do, due to gas trapping and need to keep the lungs more inflated to minimize the severity of obstruction. Orthopnea may result.

44. Inhalation Lung Scans in the Lateral Decubitus Position for a Normal Subject and COPD Patient Normal COPD No PEEP PEEP 10 Addition of 10 cm H 2 O PEEP re-opens dependent airways in COPD

45. PEEP Flow Limitation “Waterfall”

46. Adding PEEP that approximates auto-PEEP may reduce the difference in pressure between alveolus (Palv) and airway opening, thereby lowering the negative pleural (Pes) pressure needed to begin inspiration and trigger ventilation.

47. Adding PEEP Lessens the Heterogeneity of End-expiratory Alveolar Pressures and Even the Distribution of Subsequent Inspiratory Flow.

48. PEEP may offset (COPD) or add to auto-PEEP (Asthma), depending on flow limitation. Note that adding 8 cmH2O PEEP to 10 cmH2O of intrinsic PEEP may either reduce effort (Pes, solid arrow) or cause further hyper-inflation (dashed arrow). Ranieri et al, Clinics in Chest Medicine 1996; 17(3):379-94 ASTHMA COPD

49. Conventional Modes of Ventilatory Support The traditional modes of mechanical ventilation—Flow-regulated volume Assist Control (“Volume Control”, AMV, AC)) or Pressure-Targeted Assist Control (“Pressure Control”), Synchronized Intermittent Mandatory Ventilation (SIMV)—with flow or pressure targeted mandatory cycles), Continuously Positive Airway Pressure (CPAP) and Pressure Support can be used to manage virtually any patient when accompanied by adequate sedation and settings well adjusted for the patient’s needs. Their properties are discussed in the “Basic Mechanical Ventilation” unit of this series.

50. Positive Airway Pressure Can Be Either Pressure or Flow Controlled—But Not Both Simultaneously Dependent Variable Dependent Variable Set Variable Set Variable

51. Decelerating flow profile is an option in flow controlled ventilation but a dependent variable in pressure control. Decelerating Flow Pressure Control Peak pressure is a function of flow; plateau pressure is not

53. Pressure Support ‘off-switch’ is a set flow value or a set % of peak inspiratory flow. The patient with airflow obstruction may need to put on the brake with muscular effort to slow flow quickly enough to satisfy his intrinsic neural timing.

54. Tapered inspiratory ‘attack’ rate and a higher percentage of peak flow off switch criterion are often more appropriate in airflow obstruction than are the default values in PSV. Airflow Obstruction

55. Although early flows are adequate, mid-cycle efforts may not be matched by Decelerating Flow Control (VCV). Pressure Controlled breaths (PCV) do not restrict flow. Since the flow demands of severely obstructed patients may be nearly unchanging in severe airflow obstruction , decelerating VCV may not be the best choice.

57. Alveolar Pressure Airway Pressure Residual Flows

59. P aw Reflects Effort and Dys-Synchrony During Constant Flow Ventilation Deformed Airway Pressure Waveforms

60. High Pressure Alarm Variable Tidal Volume or Pressure Limit Alarm During Pressure Control

66. Compliance Changes During Pressure Controlled Ventilation

67. PRVC Automatically Adjusts To Compliance Changes

68. Several modes allow the physician to allow for variability in patient efforts while achieving a targeted goal. Volume support monitors minute ventilation and tidal volume , changing the level of pressure support to achieve a volume target. Volume assured pressure support allows the patient to breathe with pressure support, supplementing the breath with constant flow when needed to achieve the targeted tidal volume within an allocated time. Proportional assist (see later) varies pressure output in direct relation to patient effort.

70. Inverse Ratio Airway Pressure Release (APRV), and Bi-Level (Bi-PAP)

72. Unlike PCV, BiPAP Allows Spontaneous Breathing During Both Phases of Machine’s Cycle

73. Bi-Level Ventilation

74. Bi-Level Ventilation With Pressure Support

77. Proportional Assist Amplifies Muscular Effort Muscular effort (P mus ) and airway pressure assistance (P aw ) are better matched for Proportional Assist (PAV) than for Pressure Support (PSV).

82. Neural Control of Ventilatory Assist (NAVA) Neuro-Ventilatory Coupling Central Nervous System  Phrenic Nerve  Diaphragm Excitation  Diaphragm Contraction  Chest Wall and Lung Expansion  Airway Pressure, Flow and Volume New Technology Ideal Technology Current Technology Ventilator Unit

83. Electrode Array in Neurally Adjusted Ventilatory Assist (NAVA) Sinderby et al, Nature Medicine ; 5(12):1433-1436

84. NAVA Provides Flexible Response to Effort Volume P AW D GM EMG Sinderby et al, Nature Medicine ; 5(12):1433-1436

86. External and Tracheal Pressures Differ Because of Tube Resistance ATC offsets a fraction of tube resistance

87. Valve Control Maintains Tracheal Pressure During ATC Pressure Support Pressure Support ATC ATC Fabry et al, ICM 1997;23:545-552

88. ATC Adjusts Inspiratory Pressure to Need Postop Critically Ill

90. Preparation: Factors Affecting Ventilatory Demand

92. The frequency to tidal volume ratio (or rapid shallow breathing index, RSBI) is a simple and useful integrative indicator of the balance between power supply and power demand. A rapid shallow breathing index < 100 generally indicates adequate power reserve. In this instance, the RSBI indicated that spontaneous breathing without pressure support was not tolerable, likely due in part to the development of gas trapping. Even when the mechanical requirements of the respiratory system can be met by adequate ventilation reserve, congestive heart failure, arrhythmia or ischemia may cause failure of spontaneous breathing.

93. Integrative Indices Predicting Success

94. Measured Indices Must Be Combined With Clinical Observations

95. Three Methods for Gradually Withdrawing Ventilator Support Although the majority of patients do not require gradual withdrawal of ventilation, those that do tend to do better with graded pressure supported weaning than with abrupt transitions from Assist/Control to CPAP or with SIMV used with only minimal pressure support.