1. High Frequency Oscillatory Ventilation
David R. Gibson BS RRT RCP

2. What kills everyone?
Lack of Oxygen to the brain

3. Living cells need oxygen!

4. Aerobic Cellular Metabolism
Glucose
The basis of life:
Aerobic Cellular Metabolism
CO2
ATP
H2O

5. Aerobic cellular metabolism
ATP (Adenosine Triphosphate) is the “intracellular currency of life”….a “nanomachine” that fuels biologic processes.
ATP in mammals is primarily synthesized from aerobic respiration, that is: cellular metabolism.
Oxygen is required as the final electron acceptor in cellular metabolism…without which the process halts.

6. How much O2 do we need? VO2 is 200 ml/min at rest.
VO2 is 200 ml/min at rest
With exertion can be 10 times that high
The oxygen in this volume of air is used every minute at rest

7. Oxygen’s journey
Hb rich RBCs (15g per 100ml blood) pick up oxygen—via simple diffusion—through a membrane separating blood from an oxygen rich alveolar environment:
PAO2 = [(PB-47).21]-PCO2(1.25)
The amount (in ml) of oxygen contained in 100 ml of blood is called Oxygen Content (CaO2):
CaO2 =[(Hb X 1.34 X SaO2) + (PaO2 X .003)]
RBCs carrying oxygen to the cell are delivered by the cardiac output (Q).
DO2 = (CaO2)(Q) .

8.  Q Q SaO2 CaO2 PAO2 PaO2 Air Alveoli V/Q Diffusion
PAO2 is a theoretical “Ideal” controlled by FIO2 (FIO2 X 6)
Alveoli
PaO2 is dependent upon the state of the lung: V/Q matching, diffusion capacity, etc…
SaO2 is dependent upon the available PaO2 through the Oxy-Hb Curve Q
CaO2 is dependent upon available oxygen and adequate Hemoglobin
Delivered Oxygen is dependent upon available CaO2, and the hearts ability to deliver the blood (Q)

9. What can go wrong? The next 6 slides will address: Oxygen availability
Lung Pathology
Compromised PaO2/SaO2
Diffusion Capacity
Surface area for diffusion
V/Q matching
Shunt
Deadspace
Capacity for delivery
Carrying ability
Perfusion

10. What can go wrong? Low environmental oxygen – Low FIO2 and/or low PO2
Trapped in a bank vault
Mount Everest (PB is 1/3rd of normal) .

11. What can go wrong? Lung Pathology
Low PaO2 and therefore low SaO2 (see oxy-Hb disassociation curve) due to:
Diffusion Defect
Collapse (loss of surface area)
The lungs have a huge-thin membrane surface area for gas exchange (60 m2) to allow adequate oxygen diffusion into the capillary blood.

12. Ve/Q What can go wrong? V/Q mismatch Low – Shunt Consolidation
Atelectasis
Ve/Q

13. Brickey, DO; “Approaches to the Difficult to Oxygenate Patient” (lecture) 2011

14. Ve/Q What can go wrong? High – Deadspace Pulmonary embolus
Zone I region
Ve/Q

15. Anemic Hypoxia Circulatory Hypoxia Histotoxic Hypoxia
What can go wrong?
Low oxygen carrying capacity
Low Hb
Hb unable to carrying oxygen
Met Hb
CO-Hb
Low perfusion
Low cardiac output
Poor distribution of blood flow
Histotoxic hypoxia – cell unable to use O2
Anemic Hypoxia
Circulatory Hypoxia
Histotoxic Hypoxia

16. Of course that’s not all the lungs do…
Exhaust Carbon Dioxide through ventilation
Ve = (f)(Vt)
Maintain a constant CO2 level for pH regulation
 Ve   CO2   pH
 Ve   CO2   pH
CO2 is much less dependent upon surface area for gas exchange, and diffusion capacity, but is almost entirely dependent upon ventilation (Ve).

17. What can go wrong? Failure of breathing control
Suppression of breathing impulse – narcotics
Impairment of the muscles for breathing
Fatigue

18. Typical case involving RT
Pathology diminishing the lungs ability to create adequate PaO2
Increased
W.O.B.
Rapid /Shallow breathing pattern
Muscle
Fatigue
CO2 Retention
Respiratory Failure

19. Mechanical ventilation

20. In traditional artificial ventilation air is delivered as a positive pressure air gradient is created.
air
PIP
Pressure
Plat
Lungs
Time

21. Usually the pressure gradient required for adequate ventilation is relatively low ….the lungs have good compliance (as in this example).
700 ml
20 cmH2O
Volume
Pressure
CL= 700/20 = 35

22. Injured lungs have poor compliance resulting in high pressures to achieve adequate ventilation. High pressures further damage lungs in a vicious cycle.
700 ml
Volume
40 cmH2O
Pressure
CL= 700/40 = 18

23. Sick lungs: Ali - ARds

24. Brickey, DO; “Approaches to the Difficult to Oxygenate Patient” (lecture) 2011

25. Brickey, DO; “Approaches to the Difficult to Oxygenate Patient” (lecture) 2011

26. Brickey, DO; “Approaches to the Difficult to Oxygenate Patient” (lecture) 2011

27. Air
Over distension

28. Barotrauma
By the change of the millennium, it was clear that sick lungs could be made much worse with the application of positive pressures greater than 35cmH2O (plateau)

29. Strategies for dealing with barotrauma / volutrauma
Pressure Control Ventilation
Keep Plateau Pressures below 35 cmH2O
Results in lower tidal volumes (see below)
Low Tidal Volume Strategy
Allow CO2 to rise (Hypoventilation) down to a pH of 7.25
Dealing with these issues can dramatically improve outcomes in ARDS!

30. Strategies for dealing with Hypoxemia
PEEP
Increase FRC (surface area)
Prevents exhalation collapse resulting in
Improved compliance
Inverse Ratio Ventilation
Maintain Long Inflation hold time (increased surface area for oxygenation)
Sedation lowers oxygen utilization

31. Brickey, DO; “Approaches to the Difficult to Oxygenate Patient” (lecture) 2011

32. How does the high frequency Oscillator Meet gas exchange demands without hurting the lung?

33. Exhalation valve controls mean pressure
How it works
Exhalation valve controls mean pressure
How far diaphragm moves – Amps (P)
How often the diaphragm moves – Hz
Gas flow into circuit
van Heerde et al. Critical Care :R103   doi: /cc4968

34. High Frequency oscillator prevents lung injury
Mean
Volume
Pressure
HFOV operates in the “Safe Zone” avoiding alveolar collapse zone and the overdistention zone.

35. High Frequency oscillator benefits
Nearly constant alveolar pressure
Nearly constant alveolar volume
Lower airway pressures
Optimal lung volume

37. Initiation of HFOV
FIO2 > 60% and PEEP >10-14 while not being able to maintain SpO2 > 88%
Unable to maintain Plat < 30 cmH2O
Mean pressure > 24 on conventional ventilation
Patient requiring paralysis for oxygenation

38. Hfov – Earlier Intervention is better
ARDS Stages:
Phase 1 – Early Exudative Process
Phase 2 – Proliferative (day 5-10)
Phase 3 – Fibrotic (Day 10-14)

39. How to initiate hfov FIO2 100%
Mean pressure – use 5 cmH2O more than the mean on CMV
Increase by 1-4 to achieve optimal lung volume – diaphragm T8-T9
Be mindful of hemodynamic status
Volume
Mean Pressure
Amplitude

40. How to initiate hfov P – Amplitude Hz – 5-6 I.T. – 33%
Chest “wiggle” down to thigh
Start at 4.0
Hz – 5-6
Decrease if you can not control CO2 with amps of 90 or greater
I.T. – 33%
Volume
Mean Pressure
Amplitude

41. Hfov - oTHER Set bias flow to 25-40
Minimum needed to achieve mean/amps)
Too high could aggravate CO2 retention
Allow cuff leak – release air from cuff until the Mean drops by 5, then readjust the mean back to the previous setting

42. Weaning HFOV Wean FIO2 for desired SpO2
At 40% -60% may decrease Mean Pressure in increments of 1-3 cmH2O
Monitor lung volumes with CXR
Amplitude ( P) is weaned by increments of 5 cmH2O for desired PaCO2
Convert to CMV
when FIO2 < 40%
Mean Pressure weaned to 20-24
Improved CXR

43. Hfov waveform
Amplitude
MEAN Pressure
Hertz

44. Special Thanks to: Jason Higgins BS RRT – Carefusion
Sensormedics – Carefusion
David A. Brickey, DO