Hypoxemic Respiratory Failure
ALI and Acute Respiratory Distress Syndrome
Summary and Conclusions
Examine the causes of hypoxemic respiratory failure.
Review the pathophysiology, diagnostic criteria, clinical features, and epidemiology for acute lung injury (ALI) and ARDS.
Examine management strategies for ALI/ARDS, including mechanical ventilation, medical management, and rescue therapy for refractory hypoxemia.
Hypoxemic respiratory failure has a variety of causes and mechanisms that produce a life-threatening state that often requires high levels of supplemental oxygen and mechanical ventilation. Acute lung injury (ALI) and the more severe subset ARDS are characterized by pulmonary inflammation and development of high protein content pulmonary edema that causes severe hypoxemia. Management of ALI/ARDS focuses on managing the underlying causative condition(s) while providing mechanical ventilation designed to minimize further lung injury by using lower tidal volumes and avoiding excessive alveolar distending pressures while also minimizing repetitive alveolar collapse and recruitment with higher levels of positive end-expiratory pressure (PEEP). Additional supportive measures include minimizing accumulation of lung water, which is associated with delayed recovery. Selected interventions for ARDS often improve oxygenation and thus may have a role in rescue therapy for severe hypoxemia, including use of the neuromuscular blocking agent (NMBA) cisatracurium for the first 48 h of ARDS, prone positioning, titrating PEEP to higher than customary levels, administration of inhaled nitric oxide (INO), use of airway pressure release ventilation (APRV), high-frequency oscillatory ventilation (HFOV), and extracorporeal membrane oxygenation (ECMO). It is important to recognize that many of these interventions, including INO, APRV, and HFOV, have no evidence of improving important outcomes such as survival or ICU length of stay. Other interventions such as use of NMBA, prone positioning, high PEEP, ECMO, and moderate-dose corticosteroids have some evidence for improved outcomes—particularly for patients with severe ARDS—but remain controversial. Future research will help define optimal management.