Mechanical ventilation in the management of acute respiratory distress syndrome

The occurrence of acute respiratory distress syndrome (ARDS), is now common in intensive care units throughout the world. The diagnosis of ARDS is based on a definition that includes bilateral pulmonary infiltrates on chest radiographs, impaired oxygenation, and the absence of clinical evidence of elevated left atrial pressure. ARDS is the clinical result of a group of diverse processes, which range from physical or chemical injury, to extensive activation of innate inflammatory response. All these processes damage the integrity of the alveolar-capillary barrier causing increased alveolar-capillary permeability and an influx of protein-rich fluid into the alveolar space. This alveolar flooding results in hypoxemia, inactivated surfactant, intrapulmonary shunt, and impaired alveolar ventilation. The treatment of acute respiratory distress syndrome is largely supportive in nature, keeping patients alive while allowing their lungs to heal, and minimizing further pulmonary insult. In 1994 the National Heart, Lung, and Blood Institute (NHLBI) established the ARDS Network for the conduct of clinical trials. This is a network, supported by the National Institutes of Health, that provided the infrastructure for well-designed, multicenter, randomized trials of therapies for ARDS. The first study from this group in 2001 produced landmark data demonstrating mortality improvements in ARDS with particular mechanical ventilation strategies. Specifically, low tidal volume mechanical ventilation was demonstrated to reduce mortality by 22%. Other strategies such as high positive end expiratory pressure and prone positioning have not been shown to reduce mortality. Clinicians who are involved in the care of patients with ARDS should have a basic understanding of mechanical ventilation and the evidence guiding the mechanical ventilation strategies of these patients. Until further evidence is published, providers should adopt the use of a volume and pressure limited approach to mechanical ventilation.