High frequency oscillatory ventilation (HFOV): How does it work and how to integrate it in the concept of lung protective ventilation and of the open lung? 1) What is HFOV? Specific characteristics of HFOV 2) Basic mechanisms of gas exchange during HFOV 3) How does HFOV fit in actual concepts of lung protection? - Basic concepts of lung recruitment during HFO - What are optimal settings and how to monitor - How to set MAP when switching from CMV
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High frequency oscillatory ventilation (HFOV): How does it work and how to integrate it in the concept of lung protective ventilation and of the open lung?
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High frequency oscillatory ventilation (HFOV): How does it work and how to integrate it in the concept of lung protective ventilation and of the open lung?
1) What is HFOV?Specific characteristics of HFOV
2) Basic mechanisms of gas exchange during HFOV
3) How does HFOV fit in actual concepts of lung protection?
- Basic concepts of lung recruitment during HFO
- What are optimal settings and how to monitor
- How to set MAP when switching from CMV
HFO = HFJV = HFPPV
Patient
Humidifed Bias Flow//
“Elimination” of tidal ventilation
Slutsky AS ARRD 1988;138:175-83
Gas transport mechanisms during HFOV
Bouchut JC et al. Anesthesiology 2004; 100:1007-12
Pressure transmission CMV / HFOV :
Gerstman et al
Tracheal pressure
Endinspiration Endexpiration
CMV HFOPEEP 10, Vt 6 CDP 16
CMVHFOV
CMVHFOV
HFO
Lung volumes
The Paw is used to inflate the lung and optimize the alveolar surface area for gas exchange.
Paw = Lung Volume
Oxygenation
Oxygenation is primarily controlled by the mean airway pressure (Paw) and the FiO2 for “Diffuse Alveolar Disease”.
The Paw is used to inflate the lung and optimize the alveolar surface area for gas exchange.
Paw = Lung Volume
From the lab to the bedside: The principal concepts
Adapted from Suzuki H Acta Pediatr Japan 1992; 34:494-500
Lung Recruitment Using Oxygenation during OpenLung High-Frequency Ventilation in Preterm Infants
De Jaegere Ann et al. Am J Respir Crit Care Med 2006: 174; 639–645
Adapted from Suzuki H Acta Pediatr Japan 1992; 34:494-500
Lung Recruitment Using Oxygenation during OpenLung High-Frequency Ventilation in Preterm Infants
De Jaegere Ann et al. Am J Respir Crit Care Med 2006: 174; 639–645
Adapted from Suzuki H Acta Pediatr Japan 1992; 34:494-500
Lung Recruitment Using Oxygenation during OpenLung High-Frequency Ventilation in Preterm Infants
De Jaegere Ann et al. AJRCCM 2006: 174; 639–645
before surfactant after surfactant
The Open Lung Approach with HFOV(Lung-Lavaged Rabbits) McCulloch, Forkert, Froese ARRD 137:1185-1192,1988
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HFO-Hi HFO-Lo CMV
Percentage airways with lesions
4+Epithelialinjury
HyalineMembranes
Ventilation
Ventilation is primarily determined by the stroke volume (Delta-P) or the frequency of the ventilator.
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 (as a function of pressure-amplitude, frequency, or % inspiratory time) have the most significant affect on CO2 elimination
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.
Theory of operation
Oxygenation and CO2 elimination have been demonstrated to be decoupled with HFOV
5 Hz versus 15 Hz: does it matter?
Meyer J et al. PediatrRes 2006; 60: 401–406
5 Hz versus 15 Hz: does it matter?
Meyer J et al. PediatrRes 2006; 60: 401–406
Mean airway pressure, amplitude and frequency
MAP (CDP): recruits alveoli/airways and maintains alveolar volume it is closely related to lung volumes and oxygenation
Amplitude: there is a close relationship between pressure amplitude and tidal volume
tidal volume depends on: 1) the volume displaced by the piston or diaphragm,
2) the resistance of the airways,3) the compliance of the ventilator circuit, and4) the patient’s lung mechanics
therefore: search for visible chest vibrations
change amplitude to control ventilation (PaCO2)
Bouchut JC et al. Anesthesiology 2004; 100:1007-12
0 5 10 15 20 25 30 35
pressure (cmH2O)
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0 5 10 15 20 25 30 35
pressure (cmH2O)
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(ml)
How to set initial MAP when switching to HFOV
Recruitment concept during HFO
Adapted from Suzuki H Acta Pediatr Japan 1992; 34:494-500
Andreduce FiO2!
A recruitment procedure in iRDS
Drop in SO2
10 15 20 25 30 35
Vo
lum
e a
bove
FR
C b
y re
spitr
ace
Airway pressures
105
Recruit first the lung and then keep open the lung at the lowest pressure necessary!
Adapted from Suzuki H Acta Pediatr Japan 1992; 34:494-500
1) Lower FiO2 before CDP (=MAP)
Some bedside rules:
4) If you’re “lost” - always decrease CDP first!
3) Try to work always the highest frequency possible - increase the amplitude in a first step to correct for high pCO2
2) Always try to define lung closing pressure to assure that you will use lowest pressures required
The clinical experience:
HFO vs CMV
Elective HFOV vs CMV: Death or CLD at 36 w GA or discharge
Favors HFO Favors CMV
All trials
With volume recruitment
Cumulative Meta-Analysis: Incidence of CLD
Bollen et al. AJRCCM 2003; 168: 1150–1155
Henderson-Smart DJ Cochrane Database of Systematic Reviews 2007, Issue 3. Art. No.: CD000104. DOI: 10.1002/14651858.CD000104.pub2.
Elective HFOV versus CMV
CLD at 36-37 wks PMA or discharge
Henderson-Smart DJ Cochrane Database of Systematic Reviews 2007, Issue 3. Art. No.: CD000104. DOI: 10.1002/14651858.CD000104.pub2.
Elective HFOV versus CMV
CLD at 36-37 wks PMA or discharge
35% 39% NNT 25
Henderson-Smart DJ Cochrane Database of Systematic Reviews 2007, Issue 3. Art. No.: CD000104. DOI: 10.1002/14651858.CD000104.pub2.
Elective HFOV versus CMV
Combined Outcome: Death or CLD at 36-37 wks PMA or discharge
HFOV compared with CMV for Diffuse AlveolarDisease or Air Leak in Pediatrics Arnold et al. Crit Care Med 1994;22
Protocol: MAP was set 4-8 cm H2O > CMV-MAPDecrease FiO2 before MAP
Results:No difference in Death, Length of Vent., Air Leak.
Significant improvement in oxygenation with HFO over time.*
Less need for O2 at 30 days with HFO.* * p<0.05
HFOV is safe and improves oxygenation as well as outcome
58 Children (29 CMV, 29 HFO)
MOAT II: Overall Survival
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Pro
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rv
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Days After Randomization
CV
HFOV
30d p=0.05790d p=0.078
HFOV CVN 75 73 P/F 114 (37) 111 (42)
Derdak S Am J Respir Crit Care Med 2002; 166:801–808
Predictors of Outcome
1) Oxygenation Index Response
(OI = )
2) Entry Indicators of Compliance
(Peak Inspiratory Pressure)
MAP x FiO2 x 100 PaO2
MOAT II: Predictors of Outcome
Derdak S Am J Respir Crit Care Med 2002; 166:801–808
MOAT II: Survival - PIP 38 cmH20 (post-hoc)
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Pro
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rv
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Days After Randomization
CV
30d p=0.01990d p=0.026
HFOV
HFV-Meeting2001
Fedora M Bratisl Lek Listy 2000; 101: 8-13
Early (< 24 h) versus late (>24 hours) intervention in pediatric ARDS
Metha S et al. Crit Care Med 2001; 29:1360 –1369
Time concepts for lung protection
Neither a ventilation strategy nor a mode can repair the injured lungs
Katzenstein AL et al. Surgical pathology of non-neoplastic lung disease. Saunders, Philadelphia, 1982
First Intention HFO with early lung volume recruitment