The case for and against fluid restriction and occlusion pressure reduction in adult respiratory distress syndrome.

The justification for restricting fluid administration, or more directly, for actively trying to lower pulmonary capillary pressures during pulmonary edema, is embodied in the familiar "Starling equation." This model predicts that pulmonary edema will develop if lymph flow or changes in other so-called "safety factors" cannot compensate for increases in pulmonary capillary pressures. Numerous experimental studies support the logical extension of this paradigm, namely that reduced capillary pressures and/or reduced perfusion to acutely injured lung units will result in reduced extravascular lung water accumulation. Recent clinical observational and interventional clinical studies provide evidence that outcome is improved in patients with pulmonary edema in whom active efforts are made to reduce pulmonary capillary pressures and to achieve minimally positive fluid balance. Although most adult respiratory distress syndrome (ARDS) patients do not die from refractory hypoxemia, reduced accumulation or more rapid resolution of pulmonary edema could still improve outcome by other mechanisms. Furthermore, although a strategy of fluid restriction/diuresis could potentially increase the risk of either cardiac or renal dysfunction, currently available data suggest that this management strategy in euvolemic (and certainly in hypervolemic) ARDS patients can be pursued without clinically important deterioration in either type of organ function. Thus, on balance, a strategy of fluid restriction/diuresis should be pursued during the first few days of ARDS, while carefully monitoring and supporting the perfusion of vital organs.