There are three phases in the natural history of ARDS:
Treatment: ARDS Progress in recent therapy has emphasized the importance of general critical care of pts with ARDS in addition to lung protective ventilatory strategies. General care requires treatment of the underlying medical or surgical problem that caused lung injury, minimizing iatrogenic complications, prophylaxis to prevent venous thromboembolism and GI hemorrhage, prompt treatment of nosocomial infections, and adequate nutritional support. An algorithm for the initial management of ARDS is presented in Fig. 14-1. MECHANICAL VENTILATORY SUPPORT Pts with ARDS typically require mechanical ventilatory support due to hypoxemia and increased work of breathing. A substantial improvement in outcomes from ARDS occurred with the recognition that mechanical ventilator-related overdistention of normal lung units with positive pressure can produce or exacerbate lung injury, causing or worsening ARDS. Currently recommended ventilator strategies limit alveolar distention but maintain adequate tissue oxygenation. It has been clearly shown that low tidal volumes (≤6-mL/kg predicted body weight) provide reduced mortality compared with higher tidal volumes (12-mL/kg predicted body weight). In ARDS, alveolar collapse can occur due to alveolar/interstitial fluid accumulation and loss of surfactant, thus worsening hypoxemia. Therefore, low tidal volumes are combined with the use of positive end-expiratory pressure (PEEP) at levels that strive to minimize alveolar collapse and achieve adequate oxygenation with the lowest required FIO2. Use of PEEP levels higher than necessary to optimize oxygenation has not been proven to reduce ARDS mortality. Measurement of esophageal pressures to estimate transpulmonary pressure may help to identify an optimal level of PEEP. Other techniques that may improve oxygenation while limiting alveolar distention include extending the time of inspiration on the ventilator (inverse ratio ventilation) and placing the pt in the prone position. However, these approaches are not of proven benefit in reducing mortality from ARDS. ANCILLARY THERAPIES Pts with ARDS have increased pulmonary vascular permeability leading to interstitial and alveolar edema. Therefore, they should receive IV fluids only as needed to achieve adequate cardiac output and tissue O2 delivery as assessed by urine output, acid-base status, and arterial pressure. A recent study suggested that neuromuscular blockage with cisatracurium for 48 h could potentially reduce mortality in severe ARDS. There is not convincing evidence currently to support the use of glucocorticoids or nitric oxide in ARDS. |
Section 2. Medical Emergencies