Dr.Muhammad Asim Rana

1
High Frequency Ventilation
Dr.Asim Rana
Dr.Muhammad Asim Rana
2

• Mechanical ventilation is the cornerstone of
  supportive care for acute respiratory failure.
• In most patients, adequate gas exchange can be
  ensured while more specific treatments are
  administered.

3
Conventional Ventilation, its limitations
development of HFV
4

• High airway pressures,
• Circulatory depression, and
• Pulmonary air leaks.

5

• In patients with acute lung injury (ALI) and
  ARDS, conventional mechanical ventilation (CV)
  may cause additional lung injury.

6
Pressure Volume Curve
7
Changing Lung Volume In CV
Paw Lung Volume
8
CT 2
CT 1
CT 3
Paw CDP
CDP FRC
Continuous Distending Pressure
9
Optimized Lung Volume Safe Window

• Overdistension
• Edema fluid accumulation
• Surfactant degradation
• High oxygen exposure
• Mechanical disruption
• Derecruitment Atelectasis
• Repeated closure / re-expansion
• Stimulation inflammatory response
• Inhibition surfactant
• Local hypoxemia
• Compensatory overexpansion

Zone of Overdistention
Injury
Safe Window
Zone of Derecruitment and Atelectasis
Volume
Injury
Pressure
10

• An alternate mode of ventilation may be
  instituted in an attempt to provide adequate gas
  exchange and limit ventilator-induced lung
  injury. Approaches used in patients with severe
  lung injury include
• Inverse ratio ventilation
• Pressure-limited ventilation
• Airway pressure release ventilation
• Recruitment maneuvers
• Prone positioning
• High frequency ventilation
• Nitric oxide
• Extracorporeal CO2 removal and ECMO

11

• These adverse effects stimulated the development
  of high-frequency ventilation (HFV).
• (There was great enthusiasm for HFV during its
  early development in the 1970s and 1980s).

12

• However, the initial enthusiasm for HFV waned
  as clinical studies failed to demonstrate
  important advantages over Conventional
  Ventilation.

13
There is now renewed interest in HFV because of
increasing evidence that

• (1) CV may contribute to lung injury in patients
  with acute lung injury (ALI) and ARDS
• (2) modifications of mechanical ventilation
  techniques may prevent or reduce lung injury and
  improve clinical outcomes in these patients.

14
Potential role of HFV

• Achieving adequate gas exchange while
  protecting the lung against further injury in
  patients with ALI/ARDS.

TI - Use of ultrahigh frequency ventilation in
patients with ARDS. A preliminary report.
AU - Gluck E Heard S Patel C Mohr J Calkins
J Fink MP Landow L SO - Chest 1993 May103(5)1
413-20.
15
Introduction

• HFV is a mode of mechanical ventilation that uses
  rapid respiratory rates (respiratory rate f
  more than four times the normal rate) and small
  Vts.

16
Variations of HFV

• These may be broadly classified as
• high-frequency positive pressure ventilation
  (HFPPV),
• high-frequency jet ventilation (HFJV), and
• high-frequency oscillation (HFO).

17
HFPPV

• HFPPV was introduced by Oberg and Sjostrand in
  1969.
• HFPPV delivers small Vts (approximately 3 to 4
  mL/kg) of conditioned gas at high flow rates (175
  to 250 L/min) and frequency (f, 60 to 100
  breaths/min).

18

• The precise Vt is difficult to measure.
• Expiration is passive and depends on lung and
  chest wall elastic recoil.
• Thus, with high f, there is a risk of gas
  trapping with over distention of some lung
  regions and adverse circulatory effects.

19
HFJV

• Sanders introduced HFJV in 1967 to facilitate gas
  exchange during rigid bronchoscopy.
• In HFJV, gas under high pressure (15 to 50 lb per
  square inch)is introduced through a small-bore
  cannula or aperture(14 to 18 gauge) into the
  upper or middle portion of the endotracheal tube.

20

• Pneumatic, fluid, or solenoid valves control the
  intermittent delivery of the gas jets.
• Aerosolized saline solution in the inspiratory
  circuit is used to humidify the inspired air.
• Some additional gas is entrained during
  inspiration from a side port in the circuit.

21

• This form of HFV generally delivers a Vt of 2 to
  5 mL/kg at a f of 100 to 200 breaths/min.
• The jet pressure (which determines the velocity
  of air jets) and the duration of the inspiratory
  jet (and, thus, the inspiratory/expiratory ratio
  I/E) are controlled by the operator.

22

• Together, the jet velocity and duration determine
  the volume of entrained gas.
• Thus, the Vt is directly proportional to the jet
  pressure and I/E.

23

• As with HFPPV, expiration is passive.
• Thus, HFJV may cause air trapping.

24
High Frequency Oscillation

• Lunkenheimer et al introduced HFO in 1972.
• HFO uses reciprocating pumps or diaphragms.
• Thus, in contrast to HFPPV and HFJV, both
  expiration and inspiration are active processes
  during HFO.

25

• HFO Vts are approximately 1 to 3 mL/kg at fs up
  to 2,400 breaths/min.
• The operator sets the f, the I/E (typically
  approximately 12), driving pressure, and mean
  airway pressure (MAP).

26

• The oscillatory Vts are directly related to
  driving pressures.
• In contrast, Vts are inversely related to
  frequency.
• The inspiratory bias flow of air into the airway
  circuit is adjusted to achieve the desired MAP

27
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28
Frequency controls the time allowed (distance)
for the piston to move. Therefore, the lower the
frequency , the greater the volume displaced, and
the higher the frequency , the smaller the volume
displaced.
29
HFOV Principle





I
Amplitude Delta P Tv Ventilation
CDPFRC Oxygenation
-
-
-
-
-
E
HFOV CPAP with a wiggle !
30
Pressure transmission CMV / HFOV

• Distal amplitude measurements with alveolar
  capsules in animals, demonstrate it to be greatly
  reduced or attenuated as the pressure traverses
  through the airways.
• Due to the attenuation of the pressure wave, by
  the time it reaches the alveolar region, it is
  reduced down to .1 - 5 cmH2O.

Gerstman et al
31
Pressure transmission HFOV
P
T
32
Advantages of HFO

1. There is no gas entrainment or decompression of
   gas jets in the airway, allowing better
   humidification and warming of inspired air.
2. The risks of airway obstruction from desiccated
   airway secretions is lower.
3. In addition, active expiration permits better
   control of lung volumes than with HFPPV and HFJV,
   decreasing the risk of air trapping,
   overdistention of airspaces, and circulatory
   depression.
4. Lower I/Es (12 or 13) reduce the risk of air
   trapping.

33
Selected Features of CV HFV
34
Gas Transport During HFV
35
1.Direct Bulk Flow

• Some alveoli situated in the proximal
  tracheobronchial tree receive a direct flow of
  inspired air. This leads to gas exchange by
  traditional mechanisms of convective or bulk flow.

36
2.Longitudinal (Taylor) Dispersion

• Turbulent eddies and secondary swirling motions
  occur when convective flow is superimposed on
  diffusion. Some fresh gas may mix with gas from
  alveoli, increasing the amount of gas exchange
  that would occur from simple bulk flow.

37
3.Pendeluft

• Units can mutually exchange gas, an effect known
  as pendeluft. By way of this mechanism even very
  small fresh-gas volumes can reach a large number
  of alveoli and regions

38
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39
4.Asymmetric Velocity Profiles

• The velocity profile of air moving through an
  airway under laminar flow conditions is
  parabolic.
• Air closest to the tracheobronchial wall has a
  lower velocity than air in the center of the
  airway lumen.
• This parabolic velocity profile is usually more
  pronounced during the inspiratory phase of
  respiration because of differences in flow rates.

40

• With repeated respiratory cycles, gas in the
  center of the airway lumen advances further into
  the lung while gas on the margin (close to the
  airway wall) moves out toward the mouth.

41

• During inspiration, the high frequency pulse
  creates a bullet shaped profile with the central
  molecules moving further down the air way than
  those molecules found on the periphery of the
  airway.
• On exhalation, the velocity profile is blunted so
  that at the completion of each return , the
  central molecules remain further down the airway
  and the peripheral molecules move towards the
  mouth of the airway.

42
5.Cardiogenic Mixing

• Mechanical agitation from the contracting heart
  contributes to gas mixing, especially in
  peripheral lung units in close proximity to the
  heart.

43
6.Molecular Diffusion

• As in other modes of ventilation, this mechanism
  may play an important role in mixing of air in
  the smallest bronchioles and alveoli, near the
  alveolocapillary membranes.

44
ALI/ARDS
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• Chest Radiographs CT Images

47

• Patients with ALI/ARDS frequently develop acute
  respiratory failure.
• Physiologic dead space typically is also
  elevated, which increases the minute ventilation
  required to maintain normal arterial Paco2 and pH.

TI - High-frequency percussive ventilation
improves oxygenation in trauma patients with
acute respiratory distress syndrome a
retrospective review.AU - Eastman A Holland D
Higgins J Smith B Delagarza J Olson C
Brakenridge S Foteh K Friese RSO - Am J Surg.
2006 Aug192(2)191-5.
48
Our Rescue here is Mechanical Ventilation

• BUT IT IS NOT EASY

49
Ventilator Associated Lung Injury

• Uneven distribution of Tidal Volumes
• Pro inflammatory mediators

50
Mechanisms of VALI in ALI/ARDS

1. Ventilation of lung regions with higher
   compliance may be injured by excessive regional
   end inspiratory lung volumes (EILVs).
2. Injury may occur in small bronchioles when they
   snap open during inspiration and close during
   expiration.
3. Pulmonary parenchyma at the margins between
   atelectatic and aerated units may be injured by
   excessive stress from the interdependent
   connections between adjacent units.

51

• These last two mechanisms are frequently
  described with the term shear forces and may be
  important mechanisms of lung injury when
  ventilation occurs with relatively low end
  expiratory lung volumes (EELVs) in patients with
  ALI/ARDS.

52
Injury From Excessive EILVs

• The lungs of patients with ALI/ARDS are
  susceptible to excessive regional EILV and over
  distention injury
• High inspiratory airway pressures (peak and
  plateau).

53
Volutrauma

• Excessive lung stretch, rather than pressure, is
  more likely to be the injurious force.
• Thus, there is increasing use of the term
  volutrauma to refer to the stretch-induced injury
  of excessive inspiratory gas volume.

54
Injury From Ventilation at Low EELVs

• Positive end-expiratory pressure (PEEP) has lung
  protective effects during mechanical ventilation
  in isolated lungs, and in intact and open-chest
  animals.

55

• Effect of PEEP on edema with large lung volumes
• Injury caused by ventilation with large Vt and
  low PEEP.
• Effects of smaller Vts and higher PEEPs despite
  similar EILVs.
• The effect of end-expiratory atelectasis on lung
  injury.

56
PEEP Good Or Bad
57

• These and other studies provide convincing
  evidence that PEEP has lung protective effects
  during mechanical ventilation.
• However, PEEP also can contribute to lung injury
  by raising EILV unless Vt is simultaneously
  reduced.
• Moreover, PEEP may cause circulatory depression
  from increased pulmonary vascular resistance and
  decreased venous return.

58
CV-Based Lung Protective Strategies

• CV strategies designed to protect the lung from
  VALI have been tested in several clinical trials.

59
Studies With Reduced EILV

• In two case series of patients with severe ARDS
  (a total of approximately 100 patients),
  ventilation with small Vts (reduced EILVs) was
  associated with mortality rates that were
  substantially lower than rates predicted from the
  patients acute physiology and chronic health
  evaluation (APACHE) II scores.

Ventilation with lower tidal volumes as compared
with traditional tidal volumes for acute lung
injury and the acute respiratory distress
syndrome. N Engl J Med 2000 3421301.
60
In contrast

• A large multicenter trial with 861 patients with
  ALI/ARDS found substantial improvements in
  clinical outcomes in the small Vt group.
• The mortality rate prior to discharge home with
  unassisted breathing was significantly reduced
  (31 vs 40, respectively p , 0.01) among
  patients randomized to the small Vt strategy.

61
Studies With Reduced EILV and Increased EELV

• A clinical trial in 53 patients with severe
  ARDS compared a traditional CV approach with an
  approach designed to protect the lung from VALI
  resulting from both excessive EILV and inadequate
  EELV.

62

• In the lung-protection group, pressure limited
  modes were used with Vts 6 mL/kg and peak
  inspiratory pressures 40 cm H20 to reduce EILV.
  Increased EELV was achieved, raising PEEP.
• Frequent recruitment maneuvers were
• introduced to further increase EELV, and
  additional measures were taken to avoid
  undesirable collapse or derecruitment of some
  lung regions.

63

• The lung protection approach was associated with
  an improved 28-day survival rate and weaning
  rate.
• In hospital mortality rate was also reduced

Brower RG, Shanholtz CB, Fessler HE, et al.
Prospective randomized, controlled clinical trial
comparing traditional vs reduced tidal volume
ventilation in ARDS patients. Crit CareMed 1999
2714921498
64
Summary Lung Protective Modes of CV

• The body of experimental evidence strongly
  suggests that a lung protective strategy with
  smaller EILV and higher EELV will reduce VALI and
  improve outcomes in patients with ALI/ARDS.

65
Limitations

• Increasing EELV (with higher PEEPs),
  especially when it is used in combination with
  lower EILVs (smaller Vts) during CV may cause
• hypoventilation
• respiratory acidosis
• Dyspnea
• circulatory depression
• increased cerebral blood flow
• risk for intracranial hypertension
• increase the requirements for heavy sedation and
  neuromuscular blockade.

66
Rationale for HFV-Based Lung ProtectiveStrategies
67
HFV Advantages over CV

• 1. HFV uses very small VTs. This allows the use
  of
• higher EELVs to achieve greater levels of lung
• recruitment while avoiding injury from excessive
• EILV.
• 2. Respiratory rates with HFV are much higher
• than with CV. This allows the maintenance of
• normal or near-normal Paco2 levels, even with
• very small Vts.

TI - High-frequency percussive ventilation
improves oxygenation in trauma patients with
acute respiratory distress syndrome a
retrospective review.AU - Eastman A Holland D
Higgins J Smith B Delagarza J Olson C
Brakenridge S Foteh K Friese RSO - Am J Surg.
2006 Aug192(2)191-5.
68
HFOV PrinciplePressure curves CMV / HFOV
Injury
Injury
69
Adults Studies

• HFJV was compared to CV in a randomized trial of
  309 oncology patients with body weight gt 20 kg
  and respiratory failure requiring mechanical
  ventilation
• In another study, 113 surgical ICU patients at
  risk for ARDS were randomized to high-frequency
  percussive ventilation (HFPV) or CV
• In a 1997 case series, 17 medical and surgical
  patients (age range, 17 to 83 years) with severe
  ARDS

70
Conclusion
71

• Small Vt ventilation to reduce EILV during CV
  recently has shown to improve mortality when
  compared to a more traditional Vt approach.
• There is also abundant evidence in experimental
  animals and, more recently, in humans to suggest
  that there are lung protective effects with
  higher EELV.
• HFV, especially HFO, offers the best opportunity
  to achieve greater lung recruitment without
  overdistention while maintaining normal or
  near-normal acid-base parameters.

72
Starting on HFO
TI - A protocol for high-frequency oscillatory
ventilation in adults results from a roundtable
discussion. AU - Fessler HE Derdak S Ferguson N
D Hager DN Kacmarek RM Thompson BT Brower RG
SO - Crit Care Med. 2007 Jul35(7)1649-54.
73
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74
Diagrammatic Representation
75
SensorMedics 3100B

• Electrically powered, electronically controlled
  piston-diaphragm oscillator
• Paw of 5 - 55 cmH2O
• Pressure Amplitude from 8 - 130 cmH2O
• Frequency of 3 - 15 Hz
• Inspiratory Time 30 - 50
• Flow rates from 0 - 60 LPM

76
Indications

• Diffuse alveolar disease associated with
  decreased lung compliance, hypoxemia Oxygen
  index gt 30
• Oxygen indexFiO2Paw/PaO2100
• Pulmonary barotrauma with air leak syndrome
• CXR Pneumothorax
• Pneumomediastinum
• pneumoperitoneum

77
Contraindications

• Heterogenous lung disease
• Increased expiratory resistance

78
Initiation

• 1. Connect patient to HFO circuit
• 2. FiO2 100
• 3. Perform recruitment maneuvers

TI - Tidal volume delivery during high-frequency
oscillatory ventilation in adults with acute
respiratory distress syndrome.
AU - Hager DN Fessler HE Kaczka DW Shanholtz
CB Fuld MK Simon BA Brower RG
SO - Crit Care Med. 2007 Jun35(6)1522-9.
79
Initial Settings

• 1. FiO2 100
• 2. IE 12 ( Inspiratory Time 33)
• 3. Bias Flow 40 liters/min
• 4. Pressure amplitude (?P)
• 90cmH2O
• 5. mPaw 30 cm of H2O
• 6. frequency is determined by arterial pH
  immediately prior to HFO

80
pH frequency

• lt7.10 3-5Hz
• 7.10-7.19 4Hz
• 7.20-7.35 5Hz
• gt7.35 6Hz

81
Oxygenation

• Target SpO2 88-93 PaO2 55-80mmHg
• After initial RM decrease FiO2 in 0.05-0.1
  decrements Q2-5 minutes to target SpO2 88-93
• If resultant FiO2 is lt0.60, adjust mPaw according
  to the following chart but if SpO2 falls and you
  have to increase FiO2 above 0.60
• Perform a 2nd RM
• Reinitiate HFO with mPaw 34cmH2O
• Follow the chart again

82
Algorithm to follow
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Step
1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 FiO2
38 36 34 34 34 34 34 32 30 30 30 28 26 24 22 20 mPaw

• Fluctuation of 5 cm of H2O around set mPaw
  allowable unless oxygenation or ventilation is
  compromised otherwise increase sedation.
• Precede each increase in mPaw by a RM. Physician
  may discontinue these routine RMs at their
  discretion after 48 hours in study. Do not
  decrease mPaw more than 2 cm H2O Q 2Hrs

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If patient develops hypotension during mPaw
titration, stay at lower possible mPaw

1. Reduce mPaw to 30 cm 0f H2O or most recently
   tolerated, whichever is lower.
2. Ensure your patient is adequately filled.
3. If patient remains hypotensive despite of
   sufficient preload start pressors.
4. If lungs appear over distended on CXR and/or
   patient is unresponsive to increase in mPaw ,
   target a lower mPaw.
5. if FiO2 is gt 0.70 for gt 2 hrs intravascular
   volume is optimized try a lower mPaw.

84
Recruitment Maneuvers
TI - Combining high-frequency oscillatory
ventilation and recruitment maneuvers in adults
with early acute respiratory distress syndrome
the Treatment with Oscillation and an Open Lung
Strategy (TOOLS) Trial pilot study.AU - Ferguson
ND Chiche JD Kacmarek RM Hallett DC Mehta S
Findlay GP Granton JT Slutsky AS Stewart TESO
- Crit Care Med. 2005 Mar33(3)479-86.
85
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86
Conventional Ventilation

1. Increase FiO2 to 1.0
2. Set pressure alarm limit to 50 cm H2O.
3. Set apnea alarm to 60 seconds.
4. Change to CPAP/PS mode.
5. Assure pressure support is set at 0 tube
   compensation is off ( tube compensation should
   always be off for HFO patients).
6. Increase PEEP to 40 maintain inflation for 40
   seconds.
7. Lower PEEP to previous set level.
8. Resume previous set mode reset alarm limits.
9. Lower FiO2 to previous level.

87
When to perform a RM on HFO

• On initiation of HFO
• Immediately preceding any increase in mPAW
  dictated by the mPAW/FiO2 chart after day 2 this
  is optional at the discretion of the attending
  physician
• If a persistent desaturation (SpO2 lt88 lasting
  more than 15 minutes) occurs following an event
  likely to have caused derecruitment (e.g.
  suctioning, accidental ventilator disconnection,
  patient repositioning) after day 2 this is
  optional at the discretion of the attending
  physician

88
Recruitment Maneuvers for HFO

1. Increase FiO2 to 1.0.
2. Set high pressure alarm to 55 cm H2O.
3. Pause the oscillating membrane (? P0)
4. Eliminate a cuff leak, if present.
5. Slowly raise mPaw to 40 cm H2O over 10 seconds.
6. Maintain mPaw 40 cm H2O for 40 seconds.
7. Slowly lower mPaw over 10 seconds,to set level
   prior to RM if RM was conducted for disconnect
   or derecruitment.
8. Adjust level higher to previous if RM performed
   for persistent hypoxia.
9. Resume oscillation reset alarms.
10. Lower the FiO2.

89
Ventilation

• Goal pH 7.25-7.35 at highest possible frequency
• To minimize Vt, maximize frequency
• Adjust frequency rather than ? P 90 cm H2O to
  control pH.

90
pHgt 7.35

• Increase f by 1 Hz Q 30-60 min to pH goal or F10
  Hz.
• Decrease delta P from 90 cm only if f10 Hz pH
  gt 7.35 without cuff leak. If these criteria are
  met ,
• Decrease delta p by 10 cm H2O Q 30-60 min to
  reach pH goal.

91
pH 7.25 -7.35

• Use highest possible frequency within this goal
  range.

92
pH 7.15 -7.24

• Decrease f by 1 Hz Q 30-60 to reach pH goal or
  f4

93
pHlt 7.15

• Decrease f by 1 Hz Q 30-60 min to pH goal or f3.
• Consider IV bicarb.

94
pH lt7.0

• Ensure paralysis.
• If pH remains low for an hour other rescue
  measure should be sought.

95
Weaning

• Consider Conventional Ventilation
• FiO2lt0.40
• Amplitudelt25 cmH2O
• Frequency 10-15 Hz
• Pawlt20 cmH2O
• Ti 33

96
Important Considerations

• CXRs
• Piston centering
• Sedation paralysis
• Patient Circuit positioning
• Air way patency
• Recruitment maneuvers after suction

97
Enough???
98
References
99

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• Fessler, HE, Derdak, S, Ferguson, ND, et al. A
  protocol for high-frequency oscillatory
  ventilation in adults results from a roundtable
  discussion. Crit Care Med 2007 351649.
• Hager, DN, Fessler, HE, Kaczka, DW, et al. Tidal
  volume delivery during high-frequency oscillatory
  ventilation in adults with acute respiratory
  distress syndrome. Crit Care Med 2007 351522.

100

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101

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  High-frequency percussive ventilation improves
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102

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103

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  Combining high-frequency oscillatory ventilation
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  acute respiratory distress syndrome the
  Treatment with Oscillation and an Open Lung
  Strategy (TOOLS) Trial pilot study. Crit Care Med
  2005 33479.
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104

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