1. HFOV: Theory of Operation and Controls

2. Disclosure
Slides provided by Viasys free of charge for educational purposes
I have no financial affiliation with Viasys or any other medical company

3. Objectives
To understand the theory of operation for the 3100A
Identify appropriate ventilator manipulations for desired effects on neonates
Understand the clinical care startegies while on the 3100A HFOV

4. Dr Henderson–describes sub-anatomical Vt in panting dogs 1915

5. The respiratory dead space. Am. J. Physiol. 38:1-19.
1915 “ There may easily be a gaseous exchange sufficient to support life even when tidal volume is considerably less than deadspace”

6. History of High Frequency Ventilation
1915,
Dr. Henderson studied small tidal volumes and rapid rates
1990’s
HFOV emerged
1970’s
Success with animal studies
1995
2001
???
Dr. Emerson, Dr. Bird, Dr. Bunnell studied HFV
1980’s
Four received FDA approval
1991
2000’s
HFOV for Adults

7. 3100 A/B Theory of Operation and Controls
3100 B Approved for sale
outside the US in 1998 for
patients weighing > 35 kg
failing CMV
Approved September 24, 2001
by the FDA for sale in the US
3100A for patients weighing <35 kg

8. High Frequency Ventilation
Classified by FDA as :
A ventilator that delivers greater than 150 breaths per minute
Delivers small tidal volume, usually less than or equal to anatomical dead space volume
While HFV’s are frequently described by their delivery method (i.e. High flow interrupters, High frequency jet , or oscillator), they are classified by their exhalation mechanism
Active or passive

9. Different types of high frequency vents

10. What Causes Lung Damage?
Pressure ?
Volume ?
Are there more mechanisms at play here?

11. Stress and Strain
Stress: internal distribution of the counter force per unit of area that balances and reacts to an external load.
Transpulmonary Pressure = Paw-Ppl
Strain: Change in size or shape compared to the initial status.
Ratio between the deltaV (Vt) to FRC

12. Ventilator Induced Lung Injury
All forms of positive pressure ventilation (PPV) can result in ventilator induced lung injury (VILI)
VILI is the result of a combination of the following processes
Barotrauma
Volutrauma
Atelectrauma- Repetitive opening
and closing of the alveolus
Biotrauma

13. Barotrauma
High airway pressures during PPV can cause lung overdistension with gross tissue injury
This injury can allow the transfer of air into the interstitial tissues at the proximal airways
Clinically, barotrauma presents as pneumothorax, pneumomediastinum, pneumopericardium, and subcutaneous emphysema

14. Volutrauma
Lung overdistension can cause diffuse alveolar damage at the pulmonary capillary membrane
This may result in increased epithelial and microvascular permeability, thus, allowing fluid filtration into the alveoli (pulmonary edema)
Excessive end-inspiratory alveolar volumes are the major determinant of volutrauma

15. Atelectrauma
Mechanical ventilation at low end-expiratory volumes may be inefficient to maintain the alveoli open
Repetitive alveolar collapse and reopening of the under-recruited alveoli result in atelectrauma
The quantitative and qualitative loss of surfactant may predispose to atelectrauma

16. Acute Lung Injury and ARDS- Biotrauma
Ware and Matthay, NEJM 342 (18): 1334

17. What Hurts Lungs

18. Pressure and Volume Ventilation
During CMV, there are swings between the zones of injury from inspiration to expiration
INJURY
INJURY

19. Airway Pressure Release Ventilation
During APRV, auto-PEEP occurs due to very small release times which in theory, prevents alveolar collapse
INJURY

20. Pressure and Volume Swings
During HFOV, the entire cycle operates in the “safe window” and avoids the injury zones
INJURY??
HFOV
INJURY??

21. P-V Loop

22. Lower Inflection Point as Best Peep: Where is it really?

23. Oxygenation
The Paw is used to inflate the lung and optimize the alveolar surface area for gas exchange.
Paw = Lung Volume

24. Oscillation vs Conventional Waveform
Notice Higher mean airway pressure in HFOV
CMV swings in pressure from low to high.

25. High Frequency Ventilation
Advantages-
Enables ventilation above the “closing volume” with lower alveolar pressure swings.
Safe way of using “Super PEEP”.

26. HFOV Simplified CPAP with a wiggle CPAP used to oxygenate
Wiggle used to ventilate
We control the CPAP level with mean airway pressure (mPaw)
We control the wiggle with amplitude (P)

27. Lung Protection Strategies = Holding Lungs At High FRC
APRV ? HFO? ARDS Network?
All hold lungs at near constant lung MAP, limiting pressure swings
APRV & ARDS Network strategies are accomplished with conventional ventilator and both are less technically challenging
PCIRC cmH2O
One of the elements of lung protective stategy is to hold the lungs open at a high Functional Residual Capacity (FRC) to help establish Mean Airway Pressure (MAP). When you consider this as it relates to APRV, HFO and the ARDSnet Protocol, you can see that all three ventilation strategies achieve this. All hold lungs at near constant lung MAP, limiting pressure swings. HFO & APRV have been shown to be effective in decreasing deadspace, improving gas exchange and increasing cardiac output. The APRV & ARDS Network strategies can be accomplished with conventional ventilator and both are less technically challenging.
APRV
HFO
ARDS Network 40 30 20 10 10
-20 2 4 6 8 10
12s
11/8/2018 65 65 17 17 17 17 17

28. Mechanisms of gas exchange
Slutsky & Drazen NEJM 2002;347:630

29. Mechanisms of Gas Exchange
Fig 1
Fig 1 “Introduction to High Frequency Ventilation-ppt download” Slideplayer 33 Gas transport Mechanism… web 4/9/2018

30. Gas Flow Mechanisms- Bulk Gas Flow 1
Ventilation of alveoli close to airway opening
Bulk gas flow

31. Gas Flow Mechanisms- Pendelluft 2
Ventilation of alveoli due to non-homogenous time constants in the lung.
First described by Otis et al. 3
Due to differing time constants some alveoli get gas from other units as they collapse during the expiratory phase
Creates a “ bag of worms” or the appearance of a rippling effect

32. Gas Flow Mechanisms-Convective Dispersion from Aysmetrical Velocity Profiles 4
Asymmetrical velocity flow profiles
Swirling eddies caused by radial mixing promotes gas flow.
Also know as Taylor dispersion. Taylor first characterized this type of gas flow in
Dispersion in branching areas.

33. Gas Flow Mechanisms- Diffusion 6
Diffusion at the alveolar-capillary membrane
“Random movement due to thermal oscillation (Chang, H.K., Mechanisms of gas transport during ventilation by high-frequency oscillation., Journal of Applied Physiology, vol 56, issue 3, March 01, 1984, 560.

34. HFO Gas Flow In/Out

35. Paw is created by a continuous bias flow of gas past the resistance (inflation) of the balloon on the mean airway pressure control valve.

36. Principle of the SM 3100A HFOV
“Super-CPAP” system to maintain lung volume

37. Knob-ology 101 CO2 elimination PaO2 support Amplitude Hz
Ti (minimal effect in small endotracheal tubes)
PaO2 support
MAP
FiO2

38. Amplitude = peak to trough
Primary control of CO2 is by the stroke volume produced by the Power Setting.

39. Alveolar ventilation during CMV is defined as:
F x Vt
Alveolar Ventilation during HFV is defined as:
F x Vt 2
Therefore, changes in volume delivery have a more significant affect on CO2 elimination than frequency

40. Hz
Secondary control of PaCO2 is the set Frequency.

41. HFOV 3100B Frequency/Hertz 4 Hz 8 Hz Secondary control for ventilation
Frequency controls the time allowed for the piston to move forward and backward
Frequency has the largest impact on tidal volume than any other setting
The lower the frequency, the greater the volume displaced
4 Hz
8 Hz

42. Regulation of stroke volume
The stroke volume will increase if
The amplitude increases (higher delta P)
The frequency (Hz) decreases (longer cycle time)
Stroke volume

43. HFOV 3100B Inspiratory Time %
% IT controls the time for the movement of the piston during inhalation and therefore can assist with ventilation
Increasing % IT may also have an impact on lung recruitment by increasing delivered mPaw
% I-Time
Allows more time for piston travel resulting in larger tidal volume

44. The % Inspiratory Time also controls the time for movement of the piston, and therefore can assist with CO2 elimination.
Increasing % Inspiratory Time will also affect lung recruitment by increasing delivered Paw.
In most case adjusting the % Inspiratory time will not affect the Co2 that much.

45. Pressure transmission
Gerstmann D.

46. Hz, Tube size and % Ti on volume delivery

47. Piston Centering is automatically regulated in the 3100B by the instrument and requires no operator intervention. The 3100A requires manual adjustments

48. Oxygenation
As with any mechanical breathing device oxygenation is a function of MAP.
Mean airway pressure is set 5 cmH20 above conventional MAP to start.
FiO2 is always considered with oxygenation issues. Once the patients recruits alveoli and O2 sats improve, wean FiO2 until you are below 60%. Then wean MAP.

49. To pressurize the patient circuit, the Reset / Power Fail button must be pressed and held until the mean airway pressure is at least 5 cmH2O

50. The Start / Stop button is used to start and stop the oscillator
The Start / Stop button is used to start and stop the oscillator. The oscillator may be stopped without a complete loss of mean airway pressure.

51. Alarms

52. Preset High and Low mean airway pressure alarms.
Upon activation the oscillator will stop and the circuit pressure will vent to ambient.

53. Activation of the high mean pressure alarm will trigger the Auto Limit System.
The Auto Limit System will open the “blue” limit valve on the circuit and vent pressure.
The valve will then repressurize to it’s normal operational state.

54. After resolution of the fault condition the visual alarm can be cleared by pressing the Reset / Power Fail Button

55. Activation of the low mean airway pressure alarm will only provide audible and visual alarms.
The visual alarm will automatically reset after the fault condition has resolved

56. The battery low alarm will provide only a visual indicator when the nine volt alarm battery needs replacement.

57. The oscillatory overheated alarm will provide only a visual indicator if the linear motor temperature exceeds 150 degrees Centigrade.

58. The oscillator stopped alarm will provide audible and visual indicators if the oscillatory amplitude is at or below 7 cmH2O and the oscillatory subsystem is energized, (as indicated by the illumination of the green LED on the start stop button)

59. What is our Goal?? Break the pulmonary injury sequence!!!
Lung Recruitment
Open the lung with sustained inflation
Prevent alveolar collapse
Lung Protection
Provide small alveolar volume swings
Provide minimal alveolar pressure swings
Provide lower peak airway pressures
In order to reverse the detrimental effects we must achieve the goals outlined here.
These goals can be met by delivering optimal lung volume ( MAP), appropriate power setting ( Amplitude), at or near the resonant frequency of the lung system.

60. Earlier intervention produces better outcomes!!!!
When Should HFOV be Initiated?
If FIO2 > .60 on normal or elavated PEEP levels and unable to maintain SpO2 > 88%
High ventilatory rates
Unable to maintain Pplat < 20 cmH2O
mPaw on CV is > 24 cmH2O
Patient requiring paralysis for oxygenation
Earlier intervention produces better outcomes!!!!
Derdak S et al. Am J Respir Crit Care Med. 2002;166:

61. Initial HFOV Settings, Management and Weaning

62. Initial HFOV Settings
Adult patients needs proper sedated and/or paralyzed, not so much for pediatric patients
Oxygenation
Set FiO2 to 100% or maintain current FiO2 for sats >88
Set mPaw 5 cmH2O above the mPaw measurement during conventional ventilation
Ventilation
Set Amplitude and increase for proper chest movement
Set Frequency at appropriate setting for patient size
6-10 Peds
11-15 (Neonates)
Set I-time % to 33
Set Bias Flow; Neonates lpm, bigger peds lpm

63. Oxygenation -Clinical Guidelines
Initiate HFOV
FiO2 of 1.0 or FiO2 for SpO2 > 88%
mPaw of 5 cmH2O greater than mPaw on CMV
Increase mPaw by 1-4 cmH2O to achieve optimal lung volume
Optimal lung volume is determined by increasing SpO2 while maintain FiO2 or weaning FiO2
Maintain mPaw while weaning FiO2 to < .60

64. Oxygenation - Clinical Guidelines
Follow CXR 1 hour post initiation to assess lung expansion, then daily.
Degree of opacification
What is the shape of the diaphragm?
Evidence of rib scalloping?
Normal cardiac borders
Should be able to wean FiO2 to < .60 in first 12 hours
If unable to reach FiO2 .60, consider recruitment of collapsed alveoli by increasing mPaw (sustained inflation)

65. Oxygenation - Clinical Guidelines
Ensure adequate intravascular volume and cardiac output
Consider volume loading or initiate inotropes
Improves V/Q matching
High intrathoracic pressures can impede venous return and adversely affect cardiac output
Closely monitor hemodynamic status
Utilize pulse oximeters and to set appropriate HFOV settings in between ABGs

66. Oxygenation Strategies
 mPaw until SpO2 stabilizes % and begin to FiO2 to 60%
Avoid hyperinflation on CXR
Optimize preload, myocardial function

67. Ventilation – Clinical Guidelines
Amplitude
Set for adequate chest wiggle
Clavicle to groin in neonates
Frequency
Set for appropriate patient size
I-time %
Set to 33%

68. Other Strategy for Ventilation- Non Factor in uncuffed E.T.T.
If CO2 retention persists, decreasing cuff pressure to allow gas to escape around the ET tube
This will move the fresh gas supply from the wye connector to the tip of the ET tube
Adjust flow to increase mPaw by 5 – 7 cmH2O, Deflate cuff to drop mPaw to ordered mPaw

69. Other Considerations of HFOV
Adequate sedation and paralysis
May need less
Consider ETT cuff leak
Pressures will vary
May need to deflate cuff and increase bias flow to allow CO2 to escape
Need to Travel
HFOV patients cannot travel on machine
Aerosolized nebulizers
Normally not given with SVN due to the nature of gas flow in the circuit and patient. New Aerogen nebulizers have been shown to deliver medication in vivo. 7

70. Assessment Chest Wiggle factor (CWF)
Evaluate upon initiation and follow closely after that
CWF absent or diminished
clinical sign that the airway or ET tube may be obstructed
CWF present on one side only
indication that the ET tube has slipped down a primary bronchus
pneumothorax may be present
Check the position of the ET tube or obtain a CXR
Reassess CWF following any position change

71. Assessment Auscultation Breath sounds
Identifying normal “breathsounds” is difficult unless spontaneous breathing (pause oscillations)
HFOV is not ventilation with a bulk flow of gas through the airway so “spontaneous breath sounds” are not present.
Don’t just hang up your stethoscope - Listen anyway!
Listen to the “intensity or sound” that the piston makes, it should be equal throughout
If not the same sound, re-assess the patient to determine if a chest x-ray is necessary at this time

72. Assessment Auscultation- Heart or GI Sounds
Stop the piston (the patient is now on CPAP)
Listen to the heart or GI sounds quickly (how long can you hold your breath)
Start the piston back up
Removing the patient from the ventilator may result in loss of lung volume.

73. Assessment Heart Function Mean Arterial Pressure Pulse Blood Pressure
Pulse Pressure
CVP / PWP
Perfusion Status

74. Monitoring Chest X-rays Obtain the first x-ray at 1 hour, then daily.
Do not wait greater than 4 hour mark to determine the lung volume at that time.
Paw may need to be re-adjusted accordingly.
Always obtain a CXR – if unsure as to whether the patient is hyper-inflated or has de-recruited the lung.

75. Monitoring Chest X-rays Procedure
Do not stop the piston, or re-positioning the head
Do not remove the patient from HFOV and manually ventilate
A therapist, physician, or nurse should be at bedside to assure the patency of the airway and the patient’s position.

76. Monitoring Chest x-rays: Decreased opacification
Used to “guesstimate” Lung Volume
Monitor for
Decreased opacification
Diaphragms domed not flattened or inverted
Heart borders are normalized
No evidence of “Rib Scalloping”

77. Monitoring Perfusion Status Persistent Metabolic Acidosis
Capillary re-fill
Skin turgor / color
Decreased Urine Output

78. Procedures Suctioning When: Indicated by decreased or absence CWF
Decrease in O2 saturation
Closed suction catheters may mitigate
de-recruitment
Consider temporarily  Paw or FiO2

79. Procedures Suctioning
If using a closed suction catheter remember to:
Remove the suction catheter all the way from the ET tube.
There is no need to suction on a routine basis, unless the patient has copious amounts of secretions.

80. Procedures Positioning
Assure position of head and ET tube to prevent risk of kink in ET tube or 3100A circuit
The neonate can be in any position but monitor carefully to prevent risk of extubation
“lay” the circuit in the bed with the patient

81. Procedures Humidification of bias flow
Circuit connects to commercially available humidifiers
3100A flexible circuit requires the heated wire connection to be utilized
Maintain 37 degrees C at ET tube port
Visually monitor for evidence of adequate humidification being delivered
Drain condensate frequently if necessary
Does not require special humidification as with a jet. Does not plug off like a jet.

82. Procedures Bronchodilator Therapy
Due to high Bias Flow, most medication delivered in a SVN is washed out of circuit rather than delivered to patient
Aerogen nebulizer may offer better deposition of particles based on MMAD.
Medication nebs. Have no effect when delivered through the oscillator. All medication exits the exhalation port. No med. Is delivered to the patient

83. References:
1,2,4,5,6 Chang, H.K., (1984) Mechanisms of gas transport during ventilation by high-frequency oscillation. Journal of Applied Physiology, vol 56, (3), pages
3 Otis, A. B., C.B.McKerrow, R.A. Bartlett, J. Mead, M.B. McIlroy, N.J. Selverston, and E.P. Radford, Jr. (1956) Mechanical factors in distribution of pulmonary ventilation. Journal of Applied Physiology, vol 8, pages
7 Sood, B.G., Shen,Y., Latif, Z., Galli, B., Dawe, E. J., Haacke, E. M., (2010). Effective aerosol delivery during high-frequency ventilation in neonatal pigs. Respirology, 15 (3):
Medication nebs. Have no effect when delivered through the oscillator. All medication exits the exhalation port. No med. Is delivered to the patient