Venovenous ECMO for Refractory Hypoxemia

Refractory hypoxemia may develop in a small subset of patients with acute respiratory failure despite optimal mechanical ventilation. Acute respiratory distress syndrome is the most common underlying cause and poses a significant challenge to intensivists. Various ventilatory strategies can improve oxygenation but often lack a proven survival benefit. No universally accepted definition exists for refractory hypoxemia. However, the term generally refers to inadequate arterial oxygenation despite high inspired oxygen concentrations. A recent survey underscores the variability in how intensivists define this condition. Proposed definitions in the literature include a partial pressure of oxygen (PaO2) of 60 mm Hg or lower, or a ratio of PaO2 to the fraction of inspired oxygen (FiO2) of 100 or lower on an FiO2 of 0.8 to 1.0, with positive end-expiratory pressure greater than 15 cm H2O or plateau pressures exceeding 30 cm H2O, sustained for more than 12 hours despite low tidal volumes (4–6 mL/kg). The oxygenation index—calculated as mean airway pressure × FiO2 × 100/PaO2—is also used; values greater than 40 indicate refractory hypoxemia that may warrant rescue therapy, such as extracorporeal membrane oxygenation (ECMO), particularly after failure of standard interventions, including prone positioning, neuromuscular blockade, and pulmonary vasodilators.