Benefits of Fluid Restriction

Given the evidence that excessive lung water is associated with worsened outcomes in patients with ARDS, a fundamental question is whether an aggressive approach to reducing the amount of lung water when guided by EVLW measurement or other clinical parameters can improve outcomes. The landmark Fluid and Catheter Treatment Trial (FACTT) evaluated the benefits of fluid restriction in patients with ARDS [23]. In this study, the fluid management was based on measuring central venous pressure (CVP) or pulmonary capillary wedge pressure. Patients without evidence of shock with a central venous catheter were randomized to maintain a target central venous pressure of less than 4 mmHg in the conservative group compared with 10-14 mmHg in the liberal treatment group. Patients with a pulmonary artery catheter had a target pulmonary capillary wedge pressure of less than 8 mmHg in the conservative group compared with 14-18 mmHg in the liberal strategy. Patients assigned to the conservative fluid management group had a significantly improved mean oxygenation index, the lung injury score, an increased number of ventilator-free days, and decreased length of stay in the ICU, although they demonstrated no difference in hospital mortality compared with the liberal fluid management group. Despite the importance of these findings, the exclusion of hemodynamically unstable patients or patients with renal failure makes it impossible to generalize these results or to create a simple protocol for management of the fluid status in all ARDS patients. In most patients, ARDS occurs within the context of a generalized process of systemic inflammation resulting from conditions such as severe sepsis, burn injury, hemorrhagic shock, and necrotizing pancreatitis that are responsible for hemodynamic dysfunction. A number of guidelines for these conditions recommend an aggressive and early fluid resuscitation, based on the body of evidence showing that rapid repletion of fluid deficit in shock prevents the critical decrease of oxygen delivery, attenuates the severity of multiple organ dysfunction, and reduces mortality [24-26]. However, when these conditions are complicated by coinciding ARDS, the optimal fluid management remains unknown. A study of septic patients with acute lung injury showed that mortality was increased in patients who did not receive adequate early fluid management [27]. However, excessive early fluid administration can be accompanied by intense fluid accumulation in the tissues, particularly in the lungs, leading to increase in pulmonary edema. This fluid administration dilemma forces the clinician to modify the early goal-directed resuscitation approach and consider “permissive hypovolemia” [28]. Whether this approach is optimal for ARDS patients is unclear; however, if undertaken, it is probably best implemented in the settings of advanced volumetric and metabolic monitoring.