This is a secondary cross-sectional analysis of the FACTT multi-center randomized controlled trial enrolling adult patients within 48 hours of ARDS onset from twenty medical centers across the US, some of which included more than one hospital. We studied the patients who were randomized to the pulmonary artery catheter arm of the FACTT study. The investigators included patients that had PEEP and cardiac index measurements performed within a short period of each other during the first 3 days of the FACTT study enrollment. Since FACTT had a 2x2 factorial design, half of the patients were in a 'liberal fluids' study arm, and the other half were in a 'conservative fluids' study arm.