The FLARE Four
- Airway pressure release ventilation (APRV) and high-frequency oscillatory ventilation (HFOV) are outdated modes of ventilation for acute respiratory distress syndrome (ARDS)
- It has been suggested that, in theory, these approaches may be better suited to COVID-19–associated ARDS than traditional lung protective ventilation because they might increase recruitment, decrease shunt and avoid some forms ventilator-induced lung injury
- Unlike traditional lung protective ventilation, neither HFOV nor APRV has ever been shown to reduce mortality in ARDS, and one large randomized, controlled trial of HFOV found an increase in mortality
- Traditional lung-protective ventilation—low tidal volume and minimal driving pressure—is the best approach to mechanical ventilation in COVID-19 and in ARDS more generally
Reported mortality for mechanically ventilated patients with COVID-19 ranges widely from <20% to >80%, mostly limited by incomplete data. The possibility of poorer than expected outcomes have prompted some to propose that outdated modes of ventilation, airway pressure release ventilation (APRV) and high-frequency oscillatory ventilation (HFOV), should be revived for COVID-19 patients who develop acute respiratory distress syndrome (ARDS).
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Jonah Rubin, MD, and Corey Hardin, MD, PhD, physicians in the Division of Pulmonary and Critical Care Medicine at Massachusetts General Hospital, explain these approaches and their limitations in a fast literature update posted on April 23, 2020.
Background & Evidence
APRV and HFOV have in common a relatively high mean airway pressure, which is postulated to increase recruitment and decrease shunt.
APRV, a variation of bi-level positive-pressure ventilation, involves timed cycles between high and low pressures. It can be more comfortable than conventional approaches to mechanical ventilation and thus potentially requires less sedation, but tidal volume cannot be controlled. Only one trial has compared APRV with conventional low tidal volume ventilation for patients with ARDS. The single-center, open-label study showed an increase in ventilator-free days with APRV but no mortality benefit.
HFOV, another mechanical ventilatory strategy, provides high-frequency, low-amplitude oscillations around a relatively high mean airway pressure. The airway pressure is set to optimize recruitment and the low amplitude is meant to limit ventilator-associated lung injury from volutrauma and atelectrauma. HFOV requires a specialized ventilator and extensive staff training.
Two large, multicenter, randomized controlled trials compared HFOV vs. low tidal volume ventilation in ARDS. One of them was stopped early because of significantly higher mortality in the HFOV group and the other showed no 30-day mortality benefit of HFOV. In both trials, patients on HFOV were exposed to longer periods of neuromuscular blockade and sedation.
The only ventilation strategy in ARDS for which there is high-grade evidence of a mortality benefit is traditional low tidal volume ventilation with minimal driving pressure. HFOV and APRV are not recommended for adults with COVID-19–associated ARDS.
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