Comparison of Carotid Blood Flow Measured by Ultrasound and Cardiac Output in Patients Undergoing Cardiac Surgery

In general, cerebral blood flow accounts for 10-15% of cardiac output (CO), of which about 75% is delivered through the carotid arteries. Hence, if carotid blood flow (CBF) is constantly proportional to CO with high reproducibility and reliability, it would be of great value to measure CBF as an alternative to CO. The aim of this study was to investigate the direct correlation between CBF and CO. We hypothesized that measurement of CBF could be a good substitute for CO, even under more extreme hemodynamic conditions, for a wider range of critically ill patients.Patients aged 65-80 years, undergoing elective cardiac surgery were included in this study. CBF in different cardiac cycles were measured by ultrasound: systolic carotid blood flow (SCF), diastolic carotid blood flow (DCF), and total (systolic and diastolic) carotid blood flow (TCF). CO simultaneously was measured by transesophageal echocardiography.For all patients, the correlation coefficients between SCF and CO, TCF and CO were 0.45 and 0.30, respectively, which were statistically significant, but not between DCF and CO. There was no significant correlation between either SCF, TCF or DCF and CO, when CO was <3.5 L/min.Systolic carotid blood flow may be used as a better index to replace CO. However, the method of direct measurement of CO is essential when the patient's heart function is poor.