Echocardiographic assessment
All examinations are performed by senior doctors according to the standard procedure within the first 24 hours in ICU. Mindray-M9 portable color Doppler ultrasound and a P4-2s probe (2‒4 MHz) were used to perform echocardiography. Measurements of interventricular septal end-diastolic thickness (IVSd), left ventricular end-diastolic dimension (LVDd), left ventricular ejection fraction (LVEF), pulmonary artery systolic pressure (PASP), and left ventricular diastolic function were obtained from each echocardiographic examination. With the guidance of tricuspid regurgitation detected by color Doppler, continuous wave Doppler was used to measure the maximum velocity of tricuspid regurgitation and the tricuspid valve regurgitation pressure gradient (TRPG). The PASP was estimated by TRPG plus right atrial pressure (RAP). The right ventricular inflow tunnel section, parasternal short axis, parasternal four chamber, apical four-chamber or five-chamber sections were selected according to the clarity of the image in each patient. According to the collapsibility of inferior vena cava (IVC), RAP was valued as 5, 10, or 15 mmHg, respectively6. In the case of mechanical ventilator usage, central venous pressure (CVP) was considered to be equal to RAP. The highest PASP value was used for statistical analysis. In order to ensure accuracy and repeatability, the echocardiographic data were collected by two independent senior doctors.