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High Frequency Ventillation
1. Pediatric High Frequency
Ventilation:
A Clinical Approach
Ira M. Cheifetz, MD, FCCM, FAARC
Professor of Pediatrics
Chief, Pediatric Critical Care Medicine
Medical Director, PICU
Duke Children’s Hospital
2. Pediatric ALI and ARDS
♦ HFOV: Arnold study (Crit Care Med, 1994)
but control group was pre-ARDS
pre-ARDS
Network study (i.e., large tidal volume)
♦ HFJV: No data
♦ So, why use HFV in pediatrics?
physiology
–
– pathophysiology
– clinical experience
3. High Frequency Ventilation:
A Clinical Approach
♦ Pediatric ALI / ARDS
♦ HFV: Physics and Physiology
– HFOV
– HFJV
♦ Why? When?
13. ARDS
‘Infant’ lung sitting on
consolidated lung:
♦ VT of 6 - 10 ml/kg based
T
on weight
♦ VT may be > 20 ml/kg
T
based on open lung units
14. Pulmonary Injury Sequence
Froese A, Crit Care Med, 1997
Two injury zones during mechanical ventilation:
low lung volume
♦
ventilation tears
adhesive surfaces
♦ high lung volume
ventilation over-
distends resulting
in volutrauma
15.
16. HFV Goals
♦ Establish & maintain adequate FRC
normalize lung architecture
–
improve compliance
–
– reduced PVR
– improve gas exchange
♦ Provide an adequate minute volume
while minimizing regional lung over-
distension.
17. Optimizing HFV
General Guidelines:
♦ Have a clear concept of how HFV works.
♦ Know determinants of ventilation and
oxygenation with your HFV device(s).
♦ Recognize ‘benefits’ of certain strategies
vs. ‘risks’ of complications.
♦ Match ventilator strategy to patient’s
predominant pathophysiology.
♦ Be prepared to adjust strategy as patient's
condition changes.
18. Reducing the Volume-Cost of Ventilation
Each point represents the VT that yielded PCO2 = 40 torr.
2
12
10
Tidal Volume (ml/kg)
CMV
8
6
4
HFV anatomic deadspace
2
0
30 60 90 120 180 240 300 360 420 480 540 600
Freq (bpm)
Bunnell et al. Am Rev Resp Dis. 1978;117(Part 2):289.
19. ∆P is key to controlling PaCO2
∆P = PIP – PEEP
∆P VT
X
VCO2 ≈ f x VT
For HFV, X = 1.5-2.5
20. High Frequency Ventilation:
A Clinical Approach
♦ Pediatric ALI / ARDS
♦ HFV: Physics and Physiology
– HFOV
– HFJV
♦ Why? When?
21. HFOV
♦ Tidal volume < dead space volume
♦ Frequency = 180 - 900 bpm (3 - 15 Hz)
♦ Piston displacement of gas
♦ Active, intermittent exhalation
22.
23. HFOV
Approved in 1991 for neonatal resp failure
♦
– approved for ‘early intervention’
– not classified as a ‘rescue device’
♦ Approved in 1995 for peds resp failure
– no ‘weight limit’
– for selected patients failing CMV
(OI > 13 on 2 consecutive ABGs in 6 hrs)
♦ Approved in 2001 for adult ARDS pts
– 3100B approved for pts > 35 kg
27. HFOV: Neonatal Clinical Data
RCTs of the 3100A have demonstrated:
– ↓ severity of CLD in RDS infants
– ↓ cost of hospitalization for RDS
– ↓ need for ECMO in eligible candidates
– ↓ air leak in severe RDS
30. Adult ARDS and HFOV
30 Day Mortality
p
HFOV CMV % Difference
37% 52% 29% 0.098
MOAT Trial, Am J Respir Crit Care Med, 2002.
31. Predictors of Outcome: MOAT2
OI = (Paw x FiO2 x 100) / PaO2
2 2
♦ OI at 16 hrs was the only significant
predictor of mortality in a stepwise
logistic regression analysis.
♦ OI 15 at 16 hrs → 35% mortality
♦ OI 25 at 16 hrs → 55% mortality
MOAT Trial, Am J Respir Crit Care Med, 2002.
32. Conclusions: MOAT2
♦ HFOV for treatment of severe ARDS has a
90% predictive value for reducing mortality
by 29%.
♦ Trend in ↓ mortality (20%) is recognizable
at 6 mos.
♦ Benefits related to chronic lung changes
may exist as reflected by the small but
extended use of respiratory support in the
CMV group.
MOAT Trial, Am J Respir Crit Care Med, 2002.
33. Experience & Data Suggest
♦ Inverse relationship between prior days
of CMV & ability to ventilate
♦ > 72 hrs of CMV raised odds of CLD by
25 fold
♦ > 10 days of CMV ↑ risk for mortality
♦ OI > 42 at 48 hours ↑ risk for mortality
Arnold, Crit Care Med, 1994.
MOAT Trial, Am J Respir Crit Care Med, 2002.
34. HFOV: Clinical Indications
♦ ALI / ARDS – all ages / weights
– OI > 13 on two consecutive ABGs
within 6 hours
– ‘excessive’ PIP
♦ Air leak syndrome
35. HFOV: Gas Exchange
♦ Oxygenation and ventilation are
decoupled.
♦ PaO2 → Paw and FiO2
PaO2 FiO2
♦ PaCO2 → amplitude and frequency
PaCO2
♦ Minor exception – % inspiratory time
36. General Approach to Peds ALI
♦ Rate: based on pt weight and
anticipated resonant frequency of the
lung.
38. General Approach to Peds ALI
♦ Rate: based on pt weight and
anticipated resonant frequency of the
lung.
♦ Paw: titrate to ideal lung volume and,
thus, optimal oxygenation.
♦ Amplitude: titrate for desired
ventilation; permissive hypercapnia.
♦ % inspiratory time: generally 33%
39. A Clinical Caution….
If amplitude is ≥ 3 times Paw,
PEEP generated by HFOV is ≤ 0.
Paw Amp Hz PEEP
15 50 5 0
15 50 6 0
15 50 7 0
Bass et al; in progress.
40. High Frequency Ventilation:
A Clinical Approach
♦ Pediatric ALI / ARDS
♦ HFV: Physics and Physiology
– HFOV
– HFJV
♦ Why? When?
41. HFJV
♦ Tidal volume < dead space volume
♦ Frequency = 240 - 480 bpm
♦ ‘Jet’ pulse of gas
♦ Passive, continuous exhalation
♦ FDA approved in 1988
42. Flow Streaming Reduces Effective
Dead Space
Inspired gas jets into the airways at
high velocity but low pressure.
CO 2
CO2
Gas swirls down the airways,
splitting at bifurcations, seeking
path of least resistance in the
center of the airways.
The train of tiny tidal volume
pockets moves high pO2 gas
close to alveoli, while CO2 is
compressed against airway walls.
43. Exhalation During HFJV
CO 2
Exhaled gas swirls out CO
2
CO
2
around the incoming gas,
CO
2
sweeping the CO2-rich
CO2
deadspace gas out along
the airway walls. CO
2
This action may help
remove excess
secretions and debris.
44. HFJV: Clinical Indications
♦ Neonatal lung injury and air leak
syndrome – FDA approved
♦ Peds ALI / ARDS – not FDA approved
♦ Need for improved CO2 elimination
CO2
– ALI + bronchospasm (i.e. bronchiolitis +
pneumonitis)
– ALI with significant pulm hypertension
– RV dysfunction / passive pulm blood flow
♦ Note: weight limitation – based on pathophys
46. High Frequency Ventilation:
A Clinical Approach
♦ Pediatric ALI / ARDS
♦ HFV: Physics and Physiology
– HFOV
– HFJV
♦ Why? When?
47. HFOV
♦ Advantages
ability to generate high mean pressures while
–
limiting peak pressures
works for all size and age pts (3100 A / B)
–
FDA approved for peds ALI / ARDS
–
air leak syndrome
–
♦ Disadvantages
less efficient exhalation: intermittent, active
–
increased need for sedation and NMB
–
no indication of VT delivery or lung volume
– T
48. Pediatric Options for HFV
Early intervention
vs.
Rescue therapy
Why wait to start HFV??
49. Pediatric HFV
♦ HFV is capable of recruiting & protecting
♦
the acutely injured lung presumably
better than CMV.
♦ Time to intervention is a critical factor in
♦
determining the outcome of patients
managed with HFV.
50. Optimizing HFV
General Guidelines:
♦ Have a clear concept of how HFV works.
♦ Know determinants of ‘ventilation’ and
oxygenation with your HFV device(s).
♦ Recognize ‘benefits’ of certain settings vs.
‘risks’ of complications.
♦ Match ventilator strategy to patient’s
predominant pathophysiology.
♦ Be prepared to adjust strategy as patient
condition changes.
51. Pediatric ALI and ARDS
♦ HFV: Why use it?
– Physiology, pathophysiology, clinical
experience, and some data.
♦ CMV Modes:
– No data support any mode over another.
– Literature does support low tidal volume
ventilation. (ARDS Network, NEJM, 2000)
– HFV is the ultimate in low tidal volume
ventilation.
