Fluid Therapy for Acute Lung Injury

Abstract

Source: The National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome (ARDS) Clinical Trials Network. Comparison of two fluid-management strategies in acute lung injury. N Engl J Med. 2006;354:2564–2575; doi:10.1056/NEJMoa062200To evaluate the use of “conservative” versus “liberal” fluid management, investigators for the Acute Respiratory Distress Syndrome (ARDS) network screened 11,512 adult patients in 20 North American centers. Criteria for ARDS were a ratio of the partial pressure of arterial oxygen (PaO2) to the fraction of inspired oxygen (FiO2) of less than 300 and bilateral pulmonary infiltrates on chest radiograph without evidence of left atrial hypertension. Fluid management was guided by assessments using either a pulmonary artery catheter or a central venous catheter. Patients were assessed every 4 hours for blood pressure, urinary output, and either cardiac output or clinical assessment of circulation. The primary outcome was 60-day mortality, and secondary outcomes included ventilator- and ICU-free days as well as number of organ failure days assessed at day 28.One thousand patients were recruited with 503 randomized to “conservative” and 497 to “liberal” fluid management. Patients had similar demographic and hemodynamic characteristics at the time of enrollment. All patients received mechanical ventilation according to the ARDS Network protocol for lower tidal volumes.1Patients in the “liberal” arm had a positive fluid balance each day for the first 7 days of study ranging from 2.5 liters to 483 ml daily, compared to the “conservative” group which had a positive fluid balance only on day 1 of study, and afterwards had slightly negative fluid balance ranging from −144 ml to −408 ml daily. The in-hospital death rate at 60 days was 25% in the “conservative” arm and 28% in the “liberal” arm; however, the “conservative” arm had greater ventilator-free days (15 vs 12) compared to the “liberal” group (P<.01) and more ICU-free days (13 days vs 11 days; P<.001). The number of organ failure-free days was similar between groups with the exception of central nervous system failure, which was more common in the “conservative” group. Of note, although not statistically significant, use of dialysis was more common in the “liberal” fluid management arm (14% vs 10%). The authors concluded that “conservative” fluid management was associated with a decrease in duration of mechanical ventilation and ICU days.Dr. Bratton has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of a commercial product/device. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.Need for higher airway pressures with mechanical ventilation as well as capillary leak due to inflammatory processes both diminish intravascular volume and cardiac filling pressures and require administration of supplemental fluid to treat hemodynamic compromise. Studies have shown that failure to treat shock in children2 and adults3 increases risk of mortality. However, the present study nicely demonstrates that this initial insult is generally time-limited. Children with severe lung injury, like adult patients, gain fluid but those who gain less water have been shown to have improved survival.4 This report supports use of “conservative” fluid management to minimize positive fluid balance and decrease extravascular lung water leading to improved lung function. The authors showed that in the first day or so of acute respiratory failure all patients required supplemental fluid to support adequate hemodynamics and organ perfusion; however, over time patients tolerated diuretic therapy and lower intravascular filling pressures without development of additional organ failure. Use of less fluid was associated with shorter time of mechanical ventilation and ICU stay.Although pediatric mortality from acute lung injury is lower than for adult patients, recent mortality rates of 22%5 confirm that acute lung injury/ARDS remains an important pediatric critical illness. Application of the present study to pediatric practice requires use of age-appropriate blood pressure and careful assessment of hemodynamic status with a central venous catheter, a common pediatric ICU practice.