ARDS: ventilator management
Advanced, Clinical - Respiratory/Pulmonary
In the continuum of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), the lungs are damaged following an insult that may be of pulmonary (e.g., pneumonia, aspiration pneumonitis) or extrapulmonary (e.g., sepsis, trauma, transfusion) origin. Regardless of the source of injury, ARDS is characterized by an acute onset, bilateral airspace infiltrates on chest X-ray, and hypoxemia (PaO2/FIO2 < 300), assuming no evidence of left atrial hypertension. With damage to the alveolar epithelium, alveolar-capillary membrane, and endothelium, lung compliance progressively worsens, and hypoxemia becomes refractory. Consequently, mechanical ventilation is necessary.
Additionally, CT imaging of patients with ARDS has shown that the lung consolidation is heterogeneous. As such, the preserved, highly compliant, lung may be more prone to be exposed to higher tidal volumes and inflation pressures. It has been suggested to use positive end-expiratory pressure (PEEP) and possibly recruitment maneuvers to expand collapsed alveoli, which may also help to redistribute lung water and perhaps reduce injury related to the repeated expansion and collapse of alveoli. Trials suggest greater ventilator-free days and possibly a mortality benefit with high PEEP; however, an optimal level of PEEP remains unknown.
See also ARDS: Optimal tidal volume
See also ARDS: Prone position mech.