Currently, the gold standard method to estimate CO is the thermodilution technique, pulmonary artery catheter (PAC) and PiCCO system included, however, the invasiveness and complexity of the thermodilution technique have limited their usefulness in many clinical scenarios. By measuring the carotid blood flow, continuous carotid doppler technique has been reported to noninvasively estimate cardiac output (CO) and other parameters related to cardiac contractility and fluid status in various cardiovascular disorders. However, to the best of our knowledge, few study has been reported to evaluate the consistency of this technique in cardiac surgery patients. The aim of this study is to evaluate the tracking ability of CO changes measured by continuous carotid doppler technique in cardiac surgery patients, use the thermodilution technique as the referenced.

Inclusion Criteria:

• adult cardiac surgery patients
• with thermodilution technique monitoring
• mechanical ventilation

Exclusion Criteria:

• life threatening arrhythmia
• severe valve regurgitation
• left ventricular ejection fraction less than 30%
• patients with mechanical circulatory support