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Objectives
Describe the clinical presentation of patients with acute respiratory distress syndrome (ARDS).
Discuss the potential of developing ventilator-induced lung injury in patients with ARDS.
List the indications for mechanical ventilation for patients with ARDS.
Discuss approaches used to set the ventilator for patients with ARDS.
Describe the role of lung recruitment and the setting positive end-expiratory pressure (PEEP) by a decremental PEEP trial.
Discuss the management of severe refractory hypoxemia.
Describe the approach used to monitor patients with ARDS.
Describe the approach to ventilator liberation in patients with ARDS.
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Acute respiratory distress syndrome (ARDS) is a severe lung injury of diverse etiology. It is frequently related to sepsis and multiorgan failure, and is associated with high mortality. ARDS results in diffuse alveolar damage, pulmonary microvascular thrombosis, aggregation of inflammatory cells, and stagnation of pulmonary blood flow. Because many individuals each year develop ARDS in the United States, it consumes much of the time, energy, and resources in the ICU. It is one of the most changeling causes of ventilatory failure to manage and requires adherence to published guidelines.
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ARDS is characterized by hypoxemia and decreased pulmonary compliance. Bilateral infiltrates are present on the chest radiograph. Pao2/Fio2 less than or equal to 200, and no evidence of left heart failure has been the classic definition of ARDS. Recently ARDS has been categorized as severe (Pao2/Fio2 < 100), moderate (Pao2/Fio2 100-200), and mild (Pao2/Fio2 > 200). This classification is generally accepted but there is controversy over the conditions that should exist during the assessment. Some suggest that the classification should occur immediately on presentation with a positive end-expiratory pressure (PEEP) more than or equal to 5 cm H2O without a specific Fio2 requirement. Others have shown that persistent ARDS requires assessment 24 hours after presentation on a PEEP more than or equal to 10 cm H2O with an Fio2 more than or equal to 0.5. Regardless of the approach, the term "acute lung injury," defined by a Pao2/Fio2 more than 200 but less than or equal to 300, is no longer used to define the least severe form.
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Evaluation of ARDS by chest computed tomography (CT) reveals a very heterogeneous disease with areas of consolidation, areas of collapse that are recruitable, and areas of normal lung tissue. Rather than considering ARDS as low compliance lungs, the gas exchanging areas of the lungs should be considered of small volume when compared with normal lungs.
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The pathology of ARDS progresses through two phases, although the process may resolve at any point in either phase. The first phase is characterized by an intense inflammatory response resulting in alveolar and endothelial damage, increased vascular permeability, and ...