Protocolized APRV Versus Assist Control for ARDS

Aaron B. Holley, MD


November 27, 2017

Settling the APRV in ARDS Debate

The 2017 American Thoracic Society/European Respiratory Society guidelines on mechanical ventilation for acute respiratory distress syndrome (ARDS)[1] failed to address airway-pressure release ventilation (APRV). Although many consider APRV to be a "rescue mode" for refractory hypoxemia,[2] others argue that it minimizes ventilator-induced lung injury[3,4,5] and maintain that APRV should be the primary mode of ventilation for patients with ARDS.

A recently published, randomized trial[6] compared APRV versus the current standard of care, low-tidal-volume ventilation (LTV). The study enrolled 138 patients who met the Berlin definition for ARDS[7] and had a PaO2/FiO2 ≤ 250 mm Hg. Respiratory therapists were charged with ventilator management in both groups. The therapists followed the ARDSNet protocol in the LTV group: a tidal volume of 4-8 cc/kg ideal body weight with positive end-expiratory pressure (PEEP) adjusted using a PEEP-FiO2 table.[8] The ventilator protocol for the APRV group roughly mirrored the strategy outlined by Habashi in 2005.[3] Of importance, patients were weaned using a specific algorithm of "drop and stretch" with spontaneous breathing trials when appropriate.

The primary outcome was ventilator-free days by day 28. There was a large difference between groups in favor of APRV: 19 (interquartile range [IQR], 8-22) versus 2 (IQR, 0-15) days (P < .001). The APRV group had a high rate of successful extubation and shorter intensive care stays. Between-group differences in intensive care unit mortality (P = .053) and duration of hospitalization (P = .055) weren't significant, but a trend was seen. Sedation was lighter in the APRV group, and physiologic measures (oxygenation, compliance, plateau pressures) were superior to LTV. Driving pressures were equivalent.


In my opinion, these results were spectacular. Of course, the APRV for ARDS debate isn't over. This was a small, single-center, unblinded study. It's hard to believe the dramatic increase in ventilator-free days is due only to ventilator mode. Still, APRV proponents will argue that the physiologic improvements and lighter sedation levels prove biologic plausibility. They'll also gloat. They've been asking for a study with a protocolized, consistent, and individualized APRV titration strategy to prove efficacy.[5] Now they have it, and the results are as positive as predicted.

As for me, I'm starting to come back around. High airway pressures still give me pause, but we know that LTV doesn't entirely prevent lung injury either.[9,10] The American Journal of Respiratory and Critical Care Medicine just published a series of reviews celebrating 50 years of ARDS research. One paper in the series[11] lauded the physiologic benefits of using a nonsynchronized mode that optimizes recruitment; in other words, APRV. The same review noted a lack of clinical data to support its use. Perhaps now we have it.


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