1. High Frequency Oscillatory Ventilation
Bradley Fuhrman, MD
Professor and Chair, Department of Pediatrics
COI – but will not discuss:
Royalty Cook Catheter
Equity Medical Conservation Devices

2. HFOV is a lung protective strategy.
The natural history of acute respiratory failure is influenced by the way the lung is ventilated.
The cardinal feature of Ventilator Induced Lung Injury (VILI) is pulmonary edema formation.

3. Effects of High Pressure Ventilation
Normal, 5 45 cm H2O, cm H2O
(Dreyfuss and Saumon)

4. Over-Distension Pulmonary Edema Is Protein Rich

5. Alveolar wall tension stretches alveolar capillaries - especially corner vessels…

6. Increased Wall Tension Raises Transmural Pressure Across Corner Vessels
Interstitial Pressure
Capillary Pressure
Corner Vessel
Alveolar Septum
High lung volume and high surface tension promote transudation.

7. Traction on capillaries causes endothelial cell disruption.
allows PMNs to contact basement membrane
PMNs accumulate after several hours of VILI

8. Biotrauma Neutrophil accumulation Neutrophil activation
Cytokine elaboration
Inflammation
Increased capillary permeability to water, albumin and other proteins

9. Surfactant dysfunction or deficiency lowers the pressure surrounding pulmonary capillaries and promotes fluid flux.
Proteases that leak into alveoli with edema fluid inactivate surfactant.

10. Mechanisms of VILI
Increased vascular transmural pressure causes transudation of fluid
Surfactant dysfunction promotes capillary filtration
Direct trauma causes permeability edema
Biotrauma and inflammation promote capillary permeability and oxidative injury to cell membranes and other cell components

11. Mechanisms of VILI
Increased vascular transmural pressure causes transudation of fluid
Surfactant dysfunction promotes capillary filtration
Direct trauma causes permeability edema
Biotrauma and inflammation promote capillary permeability and oxidative injury to cell membranes and other cell components

12. Mechanisms of VILI
Increased vascular transmural pressure causes transudation of fluid
Surfactant dysfunction promotes capillary filtration
Direct trauma causes permeability edema
Biotrauma and inflammation promote capillary permeability and oxidative injury to cell membranes and other cell components

13. Mechanisms of VILI
Increased vascular transmural pressure causes transudation of fluid
Surfactant dysfunction promotes capillary filtration
Direct trauma causes permeability edema
Biotrauma and inflammation promote capillary permeability and oxidative injury to cell membranes and other cell components

14. Which clinical choices promote or avoid VILI ?

15. Volutrauma vs Barotrauma
High Vt, Paw=0
Negative Pressure Vent
High Vt, High Paw
Positive Pressure Vent
Thoracoabdominal- Strapped
High Pressure
Low Vt
VILI can occur at high lung volume despite low airway pressure…

16. Upper Inflection Point – Over-distension (Dreyfuss)
Lower Inflection Point – Opening/Closing Alveoli (Slutsky)
Upper Inflection Point
Lower Inflection Point
Lung Volume
Static Airway Pressure

18. Open Lung Strategy to Avoid VILI
PEEP > LIP
Pplateau < UIP
Amato et al (1995)

19. NIH ARDS Network Trial (PEEP not controlled)
6ml/kg vs 12 ml/kg
low TV 30% Mortality
high TV 40% Mortality

20. HFOV as an Open Lung Strategy

21. Inspiration
Piston
Bias Flow
Mushroom Exhaust Valve

22. Expiration
Piston
Bias Flow
Mushroom Exhaust Valve

23. Piston Forward
MAP
Piston Back

24. Inspiration x x x
xxx
xxx
xxx xx
xxx x
xxx
xxx x
xxx
xxx xx

25. Expiration x
xxx xx
xxx
xxx
xxx
xxx xx xx

26. Mary Ellen Avery: “It’s like stirring your coffee after you add cream

27. Open Lung Strategy – Lung Protective
Indications for HFOV
Open Lung Strategy – Lung Protective
A Rescue Strategy
Excessive Peak Pressure (Above UIP)
Air Leak at High Peak Airway Pressure
Very Low FRC Requiring High Airway Pressure to Maintain Oxygenation
Very low Compliance Limiting TV - Causing Hypercarbia
Cardiac Output Impaired by High Peak Airway Pressure

28. How to Use HFOV in an Open Lung Strategy
Set mean airway pressure between LIP and UIP
Assure Oxygenation
Increase amplitude until CO2 clearance becomes adequate

29. Setting MAP Open Lung Strategy
Generally start 5 to 7 cm H2O above MAP on conventional mechanical ventilation
Increase as needed to achieve desired oxygenation
May be limited by effect on cardiac filling
MAP is set by adjusting pressure at which mushroom valve opens.

30. Setting Amplitude Amplitude impacts pCO2 TV proportional to amplitude
Amplitude set by adjusting power (piston excursion)
Reading of amplitude is before endotracheal tube
Should see jiggle at thighs

32. Pressure amplitude is dampened by Endotracheal Tube.

33. Setting frequency Generally 3 to 6 Hz in adults
Optimal Hz is inversely proportional to weight
Reduce frequency to improve CO2 clearance

35. Optimal Tidal Volume ~ 2 ml/kg
Not Measured

36. Setting bias flow
In expiration, as piston moves back, expired air enters oscillator tubing
In early expiration may move both toward mushroom and toward piston
In late expiration, with mushroom closed, expired air can only move toward piston
Bias flow flushes gas in oscillator to eliminate CO2
Toward patient and mushroom in inspiration
Toward piston in expiration

37. Piston Forward
MAP
Bias Flow
Piston Back

38. Proof of Efficacy FDA approval based on avoidance of ECMO in MAS
Arnold et al 1994 – Better oxygenation, less barotrauma…
Bohn et al 1999 – Rev – No improvement in outcome…
Derdak et al 2001 – RCT – Safe and effective in adults…
Ritacca et al 2003 – Rev – As good as CMV…

39. Thank you…