High Frequency Oscillatory Ventilation is Dead

“High-Frequency Oscillation in Early Acute Respiratory Distress Syndrome” – the OSCILLATE Trail Investigators, The New England Journal of Medicine, February 28, 2013

Introduction

Mechanical ventilation improves patient outcomes by supplementing pulmonary function – to remove carbon dioxide and replace oxygen in the blood. There are multiple different ways to ventilate a patient, and different strategies target different physiologic parameters and different respiratory disease categories. Acute Respiratory Distress Syndrome (ARDS) is a disease pathology characterized by diffuse inflammation in the lungs and reduced ability of the lungs to oxygenate the blood. Some strategies for improving oxygenation include adding positive end-expiratory pressure and reversing the ratio of inhalation to exhalation times (a strategy known as Airway Pressure Release Ventilation (APRV)). A previous landmark study also noted the importance of reducing total lung volumes in ARDS in order to prevent pressure-induced injury (barotrauma) and overall mortality.

High frequency oscillatory ventilation (HFOV) is a strategy aimed at reducing barotrauma by making small changes in airway pressures around a set mean pressure. The mean pressure can be higher due to small peak pressures, allowing for improved oxygenation. The downside of low amplitude pressure changes is reduced air movement, and therefore reduced ventilation, which impairs gas exchange. Therefore, high frequency breaths given at greater than four times the normal rate are used to move more air in and out of the lungs and achieve adequate gas exchange. This study compared HFOV with traditional low-stretch protocol (established in the landmark ARDSnet study) with a primary outcome of in-hospital mortality.

Results

The trial was terminated early, after only 571 patients were enrolled, due to a significant increased mortality in patients being treated with HFOV. Patients on HFOV also required more vasopressors and neuromuscular blockers after therapy despite no differences in baseline requirements prior to randomization. There were no significant differences in fraction of inspired oxygen between HFOV and control, but mean airway pressures were lower in the control group.

Why We Do What We Do

Mechanical ventilation during ARDS is a supportive therapy that is aimed at maintaining oxygenation, removing carbon dioxide and minimizing barotrauma until the lungs recover from the primary insult. HFOV is a strategy that is generally used in infants and preterm infants with respiratory distress or interstitial emphysema. Due to the potential for HFOV to reduce lung injury, and previous evidence that pressure-induced injury is a major factor in mechanically ventilated patient mortality from ARDS, it was believed to be a possible improvement. However, the results of this trial definitively showed the potential for this strategy to cause harm.

The harm associated with HFOV noted here may be the result of a need for increased mean airway pressures. These pressures were determined by blood oxygenation levels and were increased to achieve an adequate level. Conventional ventilation achieved the same oxygenation with lower mean pressures, suggesting that it is a better oxygenation strategy.

It is also important to note that the HFOV strategy used here is only one of many different HFOV strategies. There are multiple other parameters that can be varied, such as inspiratory to expiratory times and amplitude of pressures. However, another independent large study comparing HFOV to conventional ventilation failed to show any difference in 30 day mortality between the two groups [2]. Given the harm shown in this study,clinical practice should avoid HFOV as a primary strategy for ARDS and more importantly, pursue the conventional ventilation strategy with low tidal volumes that has previously been shown to be beneficial.

References

1. Ferguson ND, Cook DJ, Guyatt GH, Mehta S, Hand L, Austin P, Zhou Q, Matte A,
Walter SD, Lamontagne F, Granton JT, Arabi YM, Arroliga AC, Stewart TE, Slutsky
AS, Meade MO; OSCILLATE Trial Investigators; Canadian Critical Care Trials Group.
High-frequency oscillation in early acute respiratory distress syndrome. N Engl J
Med. 2013 Feb 28;368(9):795-805. doi: 10.1056/NEJMoa1215554. Epub 2013 Jan 22.
PubMed PMID: 23339639.

2. Young D, Lamb SE, Shah S, MacKenzie I, Tunnicliffe W, Lall R, Rowan K,
Cuthbertson BH; OSCAR Study Group. High-frequency oscillation for acute
respiratory distress syndrome. N Engl J Med. 2013 Feb 28;368(9):806-13. doi:
10.1056/NEJMoa1215716. Epub 2013 Jan 22. PubMed PMID: 23339638.

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