PiCCO comprises techniques of pulse contour analysis and transpulmonary thermodilution, and can provide important information on hemodynamics and pulmonary functions. It has been widely used in critical care settings for several decades. Together with pulmonary artery catheter (PAC), it is regarded as the important tool for guiding fluid management in patients with shock or acute respiratory distress syndrome. During last two decades, many well designed clinical trials have been conducted to see whether the use of PAC would benefit patient outcome. The result consistently showed that PAC added no benefit in terms of mortality, ICU length of stay, organ failure free survival days, and the length of mechanical ventilation. Since PiCCO is relatively new to PAC, and 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.