PiCCO has been widely used in critical care settings for several decades. Together with pulmonary artery catheter, it is regarded as the important tool for guiding fluid management in patients with shock or acute respiratory distress syndrome. However, its effects on patients' outcome remain untested. The investigators study is a pilot study that is designed to test whether the use of PiCCO will improve patients' outcome, as compared to those without PiCCO monitoring.