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High-frequency oscillatory ventilation in adults

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Title: High-frequency oscillatory ventilation in adults


1
High-frequency oscillatory ventilation in adults
  • Geoff Smith
  • SICU
  • July 2007

2
Trauma with Acute Respiratory Distress Syndrome
  • JS 19yo man drove car off embankment into water
    while intoxicated. Ambulatory at scene with
    GCS15. Presenting pH 6.9. Oxygen saturation
    dropped and respiratory distress ensued,
    prompting emergent intubation in the ED.

3
(No Transcript)
4
High-Frequency Oscillatory Ventilation (HFOV)
  • Lung protective ventilation that oscillates the
    lung around a constant mean airway pressure
    higher than conventional ventilation
  • Significant pressure swings in the endotracheal
    tube, but pressure fluctuations are attenuated at
    the alveoli
  • First established for use in pediatrics cases of
    neonatal ARDS
  • No mortality benefit yet demonstrated in children
    (multiple RCTs) or adults (Multicenter
    Oscillatory Ventilation for ARDS Trial MOAT
    2002, Bollen et al. 2005)

5
Theoretical advantages of HFOV
  • Smaller VT
  • Limit alveolar overdistension
  • Higher mean airway pressure (mPaw/Pmaw)
  • More alveolar recruitment
  • Constant mPaw during inspiration and expiration
  • Preventing end-expiratory alveolar collapse

6
Gas exchange during HFOV
  • direct bulk flow
  • longitudinal (Taylor) dispersion
  • pendeluft
  • asymmetric velocity profiles
  • cardiogenic mixing
  • molecular diffusion

7
Biology of HFOV-Animal models
  • Less evidence of injury in surfactant-depleted
    rabbit lungs vs. conventional mechanical
    ventilation (CV).
  • Reduced inflammatory cytokine expression IL-1b,
    IL-6, IL-8, IL-10, TGFb, TNF
  • Reduced pathological change less alveolar
    leukocyte infiltration and airway epithelial
    damage

8
Multicenter Oscillatory Ventilation for ARDS
Trial (MOAT) - 2002 RCT
  • 13 university-affiliated medical centers,
    recruitment 1997-2000
  • Eligibility
  • age gt 16 on mechanical ventilation
  • PaO2/FiO2 lt 200 while on PEEP gt 10
  • Bilateral pulmonary infiltrates on CXR
  • No evidence of left atrial HTN
  • Exclusion
  • Weight lt 35 kg
  • Severe COPD or asthma
  • Intractable shock
  • Severe airleak
  • Nonpulmonary terminal diagnosis
  • FiO2 gt 0.80 for more than 2d

9
MOAT - 2002 RCT
  • n148, mean age 50, APACHE II score 22, PaO2/FiO2
    ratio 112, OI 25, mean CV prior to HFOV 2.8 d

10
MOAT - 2002 RCT
11
MOAT - 2002 RCT
  • Survival trend for HFOV over CV, but underpowered
    for significance

12
MOAT - 2002 RCT
  • Oxygenation Index a marker of survival
    irrespective of method

13
MOAT - 2002 RCT
  • Criticisms
  • Not powered to evaluate mortality (would need
    n199)
  • Higher VT (8 cc/kg measured wt, 10.6 cc/kg ideal
    wt) and peak Paw (38 cm H2O at 48h) in CV group
    than current ARDS Network trial standard of care
    for ARDS (6 cc/kg, 30 cm H2O)

14
Bollen et al. HFOV RCT 2005
  • ICU in London, Cardiff, Paris, Mainz
  • Eligibility
  • PaO2/FiO2 lt 200
  • Bilateral pulmonary infiltrates on CXR
  • No evidence of atrial HTN
  • Exclusion
  • Weight lt 35 kg
  • Severe COPD or asthma
  • Non-pulmonary terminal disease
  • Grade 3 or 4 air-leak
  • FiO2 gt 0.80 for 2d or CV gt 10d

15
Bollen 2005 RCT
  • n61 (37 and 24), mean age 51 and 55, APACHE II
    score 21 and 20, mean CV prior to HFOV 2.1 and
    1.5
  • Study stopped prematurely because of a low
    inclusion rate and the completion of the similar
    MOAT trial.

16
Bollen 2005 RCT
  • No difference in 30 d mortality

17
Bollen 2005 RCT
  • Oxygenation index response does not predict
    outcome in HFOV.

18
Bollen 2005 RCT
  • Post-hoc analysis better treatment effect of
    HFOV in patients with higher baseline OI.

19
Bollen 2005 RCT
  • Criticisms
  • Small number of patients
  • Differences in baseline patient characteristics
  • OI (25 HFOV vs. 18 CV)
  • PaO2 (81 HFOV vs. 93 CV)
  • Lack of explicit ventilation protocols
  • Underpowered to show differences in efficacy or
    safety

20
Conclusions
  • HFOV as safe and efficacious as lung protective
    CV in RCTs.
  • There is a trend of improved mortality with HFOV,
    but this needs to be repeated in a fully powered,
    properly controlled RCT (i.e., vs. lung
    protective CV)
  • HFOV may be more effective in patients with high
    baseline OI, but this should be studied directly.
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