April 08, 2014

Is There Any Role for High-Frequency Oscillatory Ventilation (Hfov) for Ards in 2013?

Dr. Michael Baram, Assistant Professor, Division of Pulmonary and Critical Care, at Thomas Jefferson University / Hospital comments on two sister articles in the recent issue of New England Journal of Medicine: Ferguson, et al & Young G, et al on use of high-frequency oscillation for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) in adults complicates a variety of illnesses and continues to have a high mortality rate of about 40%, despite application of the latest advances in mechanical ventilation ("lung protective ventilation" with lower tidal volumes). Over two decades, clinicians have anecdotally applied a counter-intuitive form of mechanical ventilation called high-frequency oscillatory ventilation (HFOV) with very low lung volumes (far less than anatomic dead space) and ultra-high respiratory rates. This approach has theoretical appeal based on lowering over-distension and increasing mean airway pressures (which may lower atelectrauma).

However, two controlled clinical studies published in the N Engl J Med 2013, strongly argue against the use of HFOV for either lack of benefit or for increased harm and mortality. One study by Ferguson, et al from the Canadian Clinical Trials Group (OSCILLATE) randomized 548 patients with ARDS to either HFOV or usual care. The study was terminated prior to the planned enrollment of 1200 patients due to harm. The mortality rate was 47% in the HFOV group and 35% in the control group, for a 1.33 higher odds ratio of mortality. In addition, the HFOV group required higher doses of sedatives and pressors. The second study by Young, et al (OSCAR trial) randomized about 400 patients each to the HFOV and usual care groups. They found equivalent 28 day mortality rates for both the HFOV and control groups of around 41%.

The standard of care for ARDS has been "lung protective strategy" that limits the stretch and strain on lungs by keeping each breath to 6 cc of air per kilogram of ideal body weight. This strategy was tested by the ARDS Network and the results showed a 25% reduction in mortality rate and this strategy of low tidal volume ventilation has become standard of care recommended by experts. Since then, no study to date has shown a better strategy. Investigators recognize that ARDS is a heterogeneous disease wherein different lung units may have different mechanical properties. Hence, applying a single ventilatory strategy to all the lung units as currently practiced by available ventilatory strategies is an inherent theoretical limitation.

Based on these two high profile and well organized randomized clinical trials and the accompanying editorial by Malhotra & Drazen, it is difficult to justify use of HFOV in adult ARDS in 2013 based on lack of benefit and a real potential for harm. We eagerly await other novel approaches to this common disease that complicates many medical and surgical diseases which continues to have a high mortality rate.

More Information:

High-Frequency Oscillation in Early Acute Respiratory Distress Syndrome

High-Frequency Oscillatory Ventilation on Shaky Ground

High-Frequency Oscillation for Acute Respiratory Distress Syndrome