New Ventilator Modes: Do They Help?


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Presentation of Dr. Dean Hess at 10th Pulmonary Medicine Update Course, Cairo, Egypt. Pulmonary Medicine Update Course is organized by Scribe :

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New Ventilator Modes: Do They Help?

  1. 1. New Ventilator Modes Do They Help? Dean Hess PhD RRT Assistant Director of Respiratory Care Massachusetts General Hospital Associate Professor of Anesthesia Harvard Medical School Editor in Chief Respiratory Care
  2. 3. 1970s 1980s 1990s 2000 IMV PSV PCV Closed Loop
  3. 4. New Modes <ul><li>Closed loop ventilation </li></ul><ul><ul><li>Negative feedback </li></ul></ul><ul><ul><ul><li>Adaptive control ventilation </li></ul></ul></ul><ul><ul><ul><li>Adaptive support ventilation </li></ul></ul></ul><ul><ul><li>Positive feedback </li></ul></ul><ul><ul><ul><li>Proportional assist ventilation </li></ul></ul></ul><ul><ul><ul><li>Tube compensation </li></ul></ul></ul><ul><ul><ul><li>Neurally adjusted ventilatory assist </li></ul></ul></ul><ul><ul><li>Smartcare </li></ul></ul><ul><li>Airway pressure release ventilation </li></ul><ul><li>High frequency ventilation </li></ul>
  4. 5. Closed Loop Ventilation <ul><li>Clinician sets a target (e.g., tidal volume) </li></ul><ul><li>The ventilator microprocessor compares the target value to the actual value and determines a new output value (e.g., pressure) </li></ul><ul><ul><li>Negative control : minimize difference between target and actual values; e.g., change pressure to minimize difference between actual and target tidal volume; adaptive control modes (PRVC) </li></ul></ul><ul><ul><li>Positive control : increase the difference between actual and target values; e.g., increase driving pressure with increased respiratory drive (PAV, NAVA) </li></ul></ul>
  5. 6. Adaptive Control Ventilation: Negative Feedback Control <ul><li>PCV with volume guarantee: AutoFlow, pressure-regulated volume control (PRVC), VC+, adaptive pressure ventilation (APV), volume targeted pressure control, pressure controlled volume guaranteed </li></ul><ul><li>PSV with volume guarantee: Volume Support (VS) </li></ul><ul><li>Pressure adjusts to achieve the target tidal volume: pressure changes with changes in lung mechanics, patient effort, or both </li></ul>
  6. 7. volume from ventilator = set tidal volume calculate new pressure limit pressure limit based on V T Trigger patient or ventilator Time = set inspiratory time cycle off yes yes no no same pressure limit PRVC, VC+, autoflow, APV (pressure-controlled breath) (first breath problem)
  7. 8. volume from ventilator = set tidal volume calculate new pressure limit pressure limit based on V T Trigger Pressure or Flow flow = % of peak flow cycle off yes yes no no same pressure limit Volume Support (pressure support breath) (first breath problem)
  8. 9. Adaptive Control: PRVC, AutoFlow, VC+ Effect of compliance increase (or effort increase) Branson, Respir Care 2005;50:187 Effect of compliance decrease (or effort decrease) The ventilator can take away support if patient effort increases! Tidal volume limitation is not guaranteed.
  9. 10. Tidal Volume with PRVC, AutoFlow, VC+, and VS Branson, Respir Care 2005;50:187
  10. 11. Effect of Increased Effort Jaber, Anesthesiology 2009; 110:620 APC (PRVC)
  11. 12. AVAPS: Average Volume Assured Pressure Support <ul><li>Estimates patient tidal volume over several breaths and compares it to target tidal volume </li></ul><ul><li>Gradually changes IPAP (0.5 – 1 cm H 2 O/min) to maintain tidal volume </li></ul><ul><li>Similar to PRVC, AutoFlow, and VS </li></ul>
  12. 13. Adaptive Support Ventilation: Negative Feedback Control <ul><li>Target minute ventilation: 100 ml/min/kg (IBW) </li></ul><ul><li>% Min Volume: 20 – 200% </li></ul><ul><li>Rate based on Otis minimal work equation (1950) </li></ul><ul><li>All combinations of rate/V T calculated </li></ul><ul><li>Te = 3 RC (I:E ratio) </li></ul><ul><li>PRVC or VS depending upon whether or not the patient is actively breathing </li></ul><ul><li>Available on Hamilton ventilator </li></ul>
  13. 14. Adaptive Support Ventilation apnea Over-distention (pressure limit) auto-PEEP rapid-shallow breathing (4.4 mL/kg) Safety Box Determined by IBW -
  14. 15. Adaptive Support Ventilation ↓ P, ↑ rate ↓ P, ↓ rate ↑ P, ↑ rate ↑ P, ↓ rate Correct IBW setting important May overshoot tidal volume Role in complicated cases?
  15. 16. Proportional Assist Ventilation: Positive Feedback Control P = V/C + V R . ( proportion of assist adjustable) respiratory drive end-inspiratory and expiratory pause maneuvers of 300 ms every 4 to 10 s to estimate of R and C With neuromuscular disease, drive may not translate into flow
  16. 17. P AW = V E + V R . Support adjusted to normalize WoB . WoB = ∫ P × Vdt
  17. 18. Proportional Assist Ventilation Marantz, JAP 1996; 80:397
  18. 19. Crit Care Med 2007;35:1048
  19. 20. Tube Compensation: Positive Feedback Control <ul><li>Pressure determined by inspiratory effort of the patient and the resistance of the endotracheal tube </li></ul>pressure (cm H 2 O Paw = PEEP + ΔPet flow (L/min)
  20. 21. Automatic Tube Compensation: Do We Need It? <ul><li>Estaban, Am J Respir Crit Care Med 1997;156:459 PSV or T-piece acceptable for spontaneous breathing trials </li></ul><ul><li>Straus, Am J Respir Crit Care Med 1998;157:23 Spontaneous breathing through endotracheal tube mimics work of breathing after extubation </li></ul><ul><li>Haberthur, Acta Anaesthesiol Scand 2002;46:973 </li></ul><ul><li>No difference in patient tolerance of SBT between patients randomized to tube compensation, PSV 5 cm H 2 O, or T-piece </li></ul>Does not compensate for changes in resistance that occur in-vivo; e.g., kinking or secretions
  21. 22. Neurally Adjusted Ventilatory Assistance (NAVA): Positive Feedback Control Sinderby, Nature Medicine 1999;5:1433
  22. 23. Effort/Drive support Volume Control PSV/PCV PAV/TC/NAVA APC/ASV
  23. 24. SmartCare (Draeger Evita XL) <ul><li>Ventilates the patient with conventional PSV </li></ul><ul><li>Clinician enters a “Zone of Respiratory Comfort” defined by breathing frequency, tidal volume and end-tidal PCO 2 ; SmartCare decreases or increases PSV </li></ul><ul><li>SmartCare actively reduces PSV to lowest level set by clinician (e.g., 0 cm H 2 O); if reached, performs a SBT </li></ul><ul><li>What was the control? “In the usual care arm, weaning was conducted according to usual local practice” </li></ul>Weaning duration reduced from of 5 to 3 d. Lellouche, Am J Respir Crit Care Med 2006; 174: 894
  24. 25. Airway Pressure Release Ventilation (APRV) Improved oxygenation, but is mortality improved? Transpulmonary pressure with spontaneous breaths? Alveolar ventilation Oxygenation
  25. 26. Airway Pressure-Release Ventilation (APRV) <ul><li>Several names for essentially the same mode: APRV, BiLevel BIPAP, BiVent, BiPhasic, PCV+, DuoPAP </li></ul><ul><li>Produces alveolar ventilation as an adjunct to CPAP </li></ul><ul><li>Allows spontaneous breathing at any time during the ventilator cycle </li></ul><ul><li>Minimizes hazards of high airway pressure?? </li></ul><ul><li>Decreased need for sedation?? </li></ul><ul><li>Improved ventilation of dependant lung zones? </li></ul>Sydow, AJRCCM 1994;149:1550 Putensen, AJRCCM 1999;159:1241 Putensen, AJRCCM 2001;164:43
  26. 27. Spontaneous Breathing <ul><li>During spontaneous breathing, the dependent part of the diaphragm has greatest displacement </li></ul><ul><li>Paralysis causes a cephalad shift of the end-expiratory position of the diaphragm, predominantly in the dependant region; reverses the pattern of diaphragmatic displacement </li></ul>Froese, Anesthesiology 1974;41:242
  27. 28. Transpulmonary Pressure: APRV Neumann, Intensive Care Med 2002;28:1742
  28. 29. High Frequency Oscillation (3100B Ventilator) <ul><li>Used more commonly in neonates that in adults </li></ul><ul><li>May improve PaO 2 in some patients because it provides higher mean airway pressure (PEEP) </li></ul><ul><li>Interest in its use in adults with ALI/ARDS, but evidence of better outcomes is lacking </li></ul>
  29. 30. The Evidence for New Ventilator Modes … It’s not the ventilator mode that makes a difference … … It’s the skills of the clinician that makes the difference. Any ventilator mode has the potential to do harm! High level evidence is lacking that any new ventilator mode improves patient outcomes compared to existing lung-protective ventilation strategies.