الفهرس 
Pathophysiology of Acute Respiratory Distress SyndromeOnly 14 pages are availabe for public view
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Abstract
Acute respiratory distress syndrome (ARDS) was first described as a clinical syndrome comprising obvious respiratory distress, severe hypoxemia, diffuse infiltrates on chest radiographs, and decreased lung compliance, associated with a variety of underlying medical and surgical conditions. A spectrum of acute lung injury exists in which ARDS represents the most severe end. The American-European Consensus Conference on ARDS attempted to define a milder form of injury, which they labeled acute lung injury (ALI). ARDS was first described in 1967. Until recently, most reported mortality rates exceeded 50%. However, the mortality from ALI and ARDS has decreased as laboratory and clinical studies have provided new evidence to improve therapeutic strategies.
Improved understanding of the pathogenesis of ALI and ARDS has led to important advances in their treatment, particularly in the area of ventilator-associated lung injury. Standard supportive care for ALI and ARDS should now include a protective ventilatory strategy with low tidal volume ventilation. In addition, novel modes of mechanical ventilation are being studied and may augment standard therapy in the future.
Several reports have shown that collapse of the lungs appeared to be directly related to degree of hypoventilation, and that this could be prevented by large tidal volumes, even if they were delivered intermittently. Subsequently, procedures termed ”recruitment maneuvers” began to be used, whereby sustained inflation pressures were used to recruit atelectatic regions of the lung and to improve oxygenation. Lately, recruitment maneuvers (RM) have been advocated to supplement protective ventilation strategies involving low lung volumes.
In patients with ALI/ARDS, considerable uncertainty remains regarding the appropriateness of recruitment maneuvers. The success/failure of such maneuvers may be related to the nature, phase, and/or extent of the lung injury, as well as to the specific recruitment technique. At present, the most commonly used recruitment maneuver is the conventional sustained inflation, which may be associated with marked respiratory and cardiovascular adverse effects. In order to minimize such adverse effects, a number of new recruitment maneuvers have been suggested to achieve lung volume expansion by taking into account the level and duration of the recruiting pressure and the pattern/frequency with which this pressure is applied to accomplish recruitment. Among the new types of recruitment maneuver, the following seem particularly interesting: 1) incremental increase in PEEP limiting the maximum inspiratory pressure; 2) pressure-controlled ventilation applied with escalating PEEP and constant driving pressure; 3) prolonged lower pressure recruitment maneuver with PEEP elevation up to 15 cmH2O and end-inspiratory pauses for 7 sec twice per minute during 15 min; 4) intermittent sighs to reach a specific plateau pressure in volume or pressure control mode; and 5) long slow increase in inspiratory pressure up to 40 cmH2O (RAMP). Moreover, the use of variable controlled ventilation, i.e., application of breath-by-breath variable VTs or driving pressures, as well as assisted ventilation modes such as Bi-Vent+PSV, may also prove a simple and interesting alternative for lung recruitment in the clinical scenario. Certainly, comparisons of different lung recruitment strategies and randomized studies to evaluate their impact on morbidity and mortality are warranted in patients with ALI/ARDS.