Anatomy of the ventilator


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Dr.Dean Hess' presentation at the 10th Pulmonary Medicine update Course February 2010
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Anatomy of the ventilator

  1. 1. Anatomy of the Ventilator Dean Hess PhD RRT Associate Professor of Anesthesia Harvard Medical School Assistant Director of Respiratory Care Massachusetts General Hospital Editor in Chief Respiratory Care
  2. 2. air O 2 filter filter PATIENT Microprocessor (mode and breath delivery) inspiratory valve(s) (flow, volume, pressure, F I O 2 ) expiratory valve (PEEP) humidifier electrical power atmosphere monitors & alarms
  3. 3. expired gas humidifier ventilator patient Aerosolized drug (nebulizer or MDI) filter dead space gas compression bias flow suction
  4. 4. Anesthesiology 2006;104:39
  5. 5. Crit Care Med 2007;35:260 VAP Crit Care Med 2007;35:260 Closed suction is cost-effective because the same catheter can be used multiple times; even for multiple days.
  6. 6. Humidification <ul><li>Prevents water and heat loss </li></ul><ul><ul><li>Active heated humidification </li></ul></ul><ul><ul><li>Passive heat and moisture exchanger (artificial nose): less effective; adds dead space and resistance </li></ul></ul>
  7. 7. Crit Care Med 2007; 35:2843
  8. 8. <ul><li>Both nebulizers and MDIs can be used to deliver Beta 2 -agonists to mechanically ventilated patients. </li></ul><ul><li>Careful attention to details of the technique employed for administering drugs by MDI or nebulizer to mechanically ventilated patients is critical, since multiple technical factors may have clinically important effects on the efficiency of aerosol delivery. </li></ul>Chest 2005; 127:335-371
  9. 9. Breath Delivery: Phase Variables <ul><li>Trigger: initiates inspiration </li></ul><ul><ul><li>Ventilator (time) or patient (pressure or flow) </li></ul></ul><ul><li>Control: what the ventilator controls during the inspiratory phase </li></ul><ul><ul><li>Flow (volume) or pressure </li></ul></ul><ul><li>Cycle: initiates exhalation </li></ul><ul><ul><li>Time, flow, volume, or pressure </li></ul></ul><ul><li>Baseline: present throughout the cycle </li></ul><ul><ul><li>PEEP or CPAP or EPAP </li></ul></ul>
  10. 10. Pressure-triggered breath Flow-triggered breath trigger Modern triggers are sensitive <ul><li>Trigger Difficulty : </li></ul><ul><li>auto-PEEP: increase PEEP setting </li></ul><ul><li>weakness: increase rate setting </li></ul><ul><li>Auto-Trigger : </li></ul><ul><li>- water in circuit </li></ul><ul><li>cardiac oscillations </li></ul>
  11. 11. Ventilator Breath Types <ul><li>Mandatory: either triggered or cycled by the ventilator (back-up rate) </li></ul><ul><ul><li>Volume control </li></ul></ul><ul><ul><li>Pressure control </li></ul></ul><ul><ul><li>Adaptive control (pressure varies to keep volume constant) </li></ul></ul><ul><li>Spontaneous: triggered and cycled by the patient (no back-up rate) </li></ul><ul><ul><li>Continuous positive airway pressure </li></ul></ul><ul><ul><li>Pressure support ventilation </li></ul></ul><ul><ul><li>Adaptive (pressure varies to keep volume constant) </li></ul></ul>
  12. 12. Volume Controlled Ventilation <ul><li>Fixed flow and inspiratory time </li></ul><ul><li>Fixed volume </li></ul><ul><li>Pressure varies with lung mechanics or patient effort </li></ul>Volume (mL) Pressure (cm H 2 O) Flow (L/min) Volume (mL) Pressure (cm H 2 O) Flow (L/min) constant descending ramp
  13. 13. Pressure Controlled Ventilation <ul><li>Fixed pressure and fixed inspiratory time </li></ul><ul><li>Variable inspiratory flow </li></ul><ul><li>Flow (volume) varies with lung mechanics and patient effort </li></ul>time Volume (mL) Pressure (cm H 2 O) Flow (L/min)
  14. 14. Equation of Motion Volume Ventilation E = 1/C X X P MUS + P AW = E V + R V . fixed volume and flow increased effort decreased airway pressure fixed pressure increased effort increased flow and tidal volume P MUS + P AW = E V + R V . Pressure Ventilation
  15. 15. Flow Dys-synchrony: VCV
  16. 16. Improved Synchrony
  17. 17. PCV 20 cm H 2 O, PEEP 10 cm H 2 O; Pplat 30 cm H 2 O transpulmonary pressure = 45 cm H 2 O -15 cm H 2 O Active inspiratory effort ↑↑ V T
  18. 18. Transpulmonary Pressure ventilator support patient effort
  19. 19. Kallet, Respir Care 2005;50:1623
  20. 20. Dys-Synchrony with PCV Kallet, Respir Care 2005;50:1623
  21. 21. Pressure-Controlled Inverse Ratio Ventilation <ul><li>Higher mean airway pressure </li></ul><ul><li>Improved gas exchange? </li></ul><ul><li>Auto-PEEP? </li></ul><ul><li>Hemodynamic compromise? </li></ul><ul><li>Patient comfort? </li></ul>time Volume (mL) Pressure (cm H 2 O) Flow (L/min)
  22. 22. Mireles-Cabodevila, Cleve Clin J Med 2009;76:417
  23. 23. Mandatory Breath Types constant descending ramp Volume (mL) Pressure (cm H 2 O) Flow (L/min) Volume (mL) Pressure (cm H 2 O) Flow (L/min) Volume (mL) Pressure (cm H 2 O) Flow (L/min) time time time Volume Control Pressure Control <ul><li>Fixed pressure and inspiratory time </li></ul><ul><li>Variable flow </li></ul><ul><li>Flow (volume) varies with lung mechanics and patient effort </li></ul><ul><li>Fixed flow and inspiratory time </li></ul><ul><li>Fixed volume </li></ul><ul><li>Pressure varies with lung mechanics and patient effort </li></ul>
  24. 24. Pressure Support Ventilation flow cycle patient trigger pressure limit <ul><li>Spontaneous breath type </li></ul><ul><li>patient triggered (no set rate) </li></ul><ul><li>pressure limited </li></ul><ul><li>usually flow cycled </li></ul>
  25. 25. Pressure Support Ventilation Adjustable rise time Adjustable flow cycle
  26. 26. Pressure Support and Sleep <ul><li>Pressure support causes hypocapnia </li></ul><ul><li>Lack of a back-up rate and wakefulness drive leads to central apnea and sleep fragmentation </li></ul>Parthasarathy, Am J Respir Crit Care Med 2002; 166:1423 Apneas per Hour
  27. 27. Volume-Control vs Pressure Control Evidence for better outcomes with either volume-control or pressure-control is lacking VCV PCV PSV Tidal volume Fixed Variable Variable Inspiratory flow Fixed Variable Variable Airway pressure Variable Fixed Fixed Inspiratory time Fixed Fixed Variable Rate Minimum set Minimum set Not set
  28. 28. Adaptive Pressure Control <ul><li>PCV or PSV with volume guarantee </li></ul><ul><li>Ventilator adjusts pressure to achieve target tidal volume: Autoflow, PRVC, VC+, volume support </li></ul><ul><li>Pressure changes with changes in lung mechanics, patient effort, or both </li></ul>
  29. 29. PCV+ (Drager); Bilevel (PB 840) Patroniti, Anesthesiology 2002; 96:788
  30. 30. Ventilator Modes <ul><li>Continuous mandatory ventilation (assist/control) [backup rate] </li></ul><ul><ul><li>VCV, PCV, adaptive control </li></ul></ul><ul><li>Continuous spontaneous ventilation [no backup rate] </li></ul><ul><ul><li>CPAP, PSV, PAV, adaptive control </li></ul></ul><ul><li>Synchronized intermittent mandatory ventilation </li></ul><ul><ul><li>VCV, PCV, adaptive control </li></ul></ul><ul><ul><li> pressure support </li></ul></ul>No “new” mode has been shown to improve patient outcomes compared to traditional modes
  31. 31. SIMV flow airway pressure esophageal pressure volume spontaneous breath spontaneous breaths mandatory breath
  32. 32. Ventilator Modes Continuous Mandatory Ventilation (CMV) Continuous Spontaneous Ventilation (CSV) Intermittent Mandatory Ventilation (SIMV) VCV PCV Dual Control PCIRV APRV CPAP PSV PAV NAVA VCV MMV Dual Control Bilevel Dual Control Automode ASV PCV
  33. 33. Goals When Setting The Ventilator <ul><li>Avoid alveolar over-distension: volume and pressure limitation </li></ul><ul><li>Apply PEEP to maintain alveolar recruitment or counter-balance auto-PEEP </li></ul><ul><li>Provide adequate gas exchange </li></ul><ul><li>Promote patient-ventilator synchrony </li></ul><ul><li>Avoid auto-PEEP </li></ul><ul><li>Use the lowest possible F I O 2 </li></ul>
  34. 34. Setting the Ventilator Ventilator-Induced Lung Injury Gas Exchange Patient Comfort Hemodynamics