A pulmonary artery catheter (Edwards Healthcare, Irvine, CA) was used to measure cardiac output according to the thermal dilution method (3 injections of 10ml 0.9% saline solution), systolic, diastolic and mean pulmonary arterial pressures, pulmonary artery occlusion pressure (PAOP, mmHg), central venous pressure (CVP, mmHg), and mixed venous saturation (SvO2). Mean arterial pressure (MAP, mmHg), measured using the arterial line, and heart rate (HR, bpm) were also recorded. All measurements were made at the end of expiration, before and after FC. Patients were defined as fluid responders when cardiac index increased at least 15% of baseline value.