High-frequency oscillatory ventilation in adults

Geoff SmithSICUJuly 2007

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.

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)

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

Gas exchange during HFOV

n direct bulk flown longitudinal (Taylor)

dispersionn pendeluft n asymmetric velocity profilesn cardiogenic mixing n molecular diffusion

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

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

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

MOAT - 2002 RCT

MOAT - 2002 RCT

Survival trend for HFOV over CV, but underpowered for significance

MOAT - 2002 RCT

Oxygenation Index a marker of survival irrespective of method

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)

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

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.

Bollen 2005 RCT

No difference in 30 d mortality

Bollen 2005 RCT

Oxygenation index response does not predict outcome in HFOV.

Bollen 2005 RCT

Post-hoc analysis: better treatment effect of HFOV in patients with higher baseline OI.

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

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.