High-frequency Oscillatory Ventilation From Basics to Evidence, From Evidence to Bedside

Abstract

Critical care physicians deal every day with patients suffering from acute lung injury and respiratory failure. Acute respiratory distress syndrome (ARDS) is the most severe form of acute lung injury. Mechanical ventilation remains the mainstay of supportive treatment for ARDS. There are patients with ARDS who are unable to achieve adequate gas exchange while receiving conventional mechanical ventilation. In this setting, high-frequency oscillatory ventilation (HFOV) arises as a nonconventional mode of mechanical ventilation with the potential not only of reversing severe hypoxemia, but also of minimizing ventilator-induced lung injury. HFOV is a unique mode of mechanical ventilation characterized by very low tidal volumes, lower than anatomic dead space (1 to 3 mL/kg), and a constant, high mean airway pressure. Ventilation at such low tidal volumes is possible using high respiratory cycle frequencies (3 to 20 Hz). Oxygenation and ventilation can be managed on high-frequency ventilation relatively uncoupled. Changes in oxygenation are addressed by changing mean airway pressure or the oxygen inspiratory fraction. CO2 elimination is dealt with by modifying oscillator pressure amplitude, frequency (inversely), inspiratory to expiratory ratio, and bias flow. High-grade evidence supporting the use of HFOV is scarce. This ventilation technique has proven to be at least as efficient and safe as conventional mechanical ventilation for patients with ARDS. Current literature suggests that it may be useful not only to rescue patients failing on mechanical ventilation, but also to minimize barotrauma, volutrauma, and biotrauma. Selection of candidates for high-frequency oscillation and utilization of the appropriate ventilatory strategies are key issues if benefits from this technique are to be maximized.