smith hfov adult ards july 2007
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High-frequency oscillatory ventilation in adults
Geoff Smith
SICU
July 2007
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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.
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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)
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Theoretical advantages of HFOV
Smaller VTLimit alveolar overdistension
Higher mean airway pressure (mPaw/Pmaw)More alveolar recruitment
Constant mPaw during inspiration and expirationPreventing end-expiratory alveolar collapse
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Gas exchange during HFOV
n direct bulk flown longitudinal (Taylor)
dispersionn pendeluft n asymmetric velocity profilesn cardiogenic mixing n molecular diffusion
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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
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Multicenter Oscillatory Ventilation for ARDS Trial (MOAT) - 2002 RCT
13 university-affiliated medical centers, recruitment 1997-2000 Eligibility:
age >= 16 on mechanical ventilation PaO2/FiO2 < 200 while on PEEP >= 10 Bilateral pulmonary infiltrates on CXR No evidence of left atrial HTN
Exclusion: Weight < 35 kg Severe COPD or asthma Intractable shock Severe airleak Nonpulmonary terminal diagnosis FiO2 > 0.80 for more than 2d
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MOAT - 2002 RCT
n=148, mean age 50, APACHE II score 22, PaO2/FiO2 ratio 112, OI 25, mean CV prior to HFOV 2.8 d
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MOAT - 2002 RCT
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MOAT - 2002 RCT
Survival trend for HFOV over CV, but underpowered for significance
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MOAT - 2002 RCT
Oxygenation Index a marker of survival irrespective of method
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MOAT - 2002 RCT
Criticisms:Not powered to evaluate mortality (would
need n=199)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)
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Bollen et al. HFOV RCT 2005
ICU in London, Cardiff, Paris, Mainz Eligibility:
PaO2/FiO2 < 200 Bilateral pulmonary infiltrates on CXR No evidence of atrial HTN
Exclusion: Weight < 35 kg Severe COPD or asthma Non-pulmonary terminal disease Grade 3 or 4 air-leak FiO2 > 0.80 for 2d or CV > 10d
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Bollen 2005 RCT
n=61 (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.
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Bollen 2005 RCT
No difference in 30 d mortality
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Bollen 2005 RCT
Oxygenation index response does not predict outcome in HFOV.
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Bollen 2005 RCT
Post-hoc analysis: better treatment effect of HFOV in patients with higher baseline OI.
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Bollen 2005 RCT
Criticisms:Small number of patientsDifferences in baseline patient characteristics:
OI (25 HFOV vs. 18 CV) PaO2 (81 HFOV vs. 93 CV)
Lack of explicit ventilation protocolsUnderpowered to show differences in efficacy
or safety
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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.