A diagnosis of respiratory failure was made after the determination of arterial oxygen pressure (PaO 2 ) level of less than 60 mmHg or arterial oxygen saturation (SaO 2 ) < 90%, with or without elevation of arterial PCO 2 . ARDS was diagnosed based on the criteria defined in the American-European consensus conference [9] . For the diagnosis of organ failure, the criteria by Knaus [10] were used. Multiple organ failure (MOF) was defined as the failure of more than one organ. Ventilator-associated pneumonia (VAP) was diagnosed based on the American Thoracic Society (ATS) criteria [11] . Anemia was defined by hemoglobin levels < 13.5 g/dL for males and < 12.0 g/dL for females. Hypoalbuminemia was considered when serum albumin levels were less than 3.5 g/dL.