Studies have shown that the clinical application of ultrasound to measure large blood vessels related parameters has been widely used to assess the blood volume status of patients, with the advantages of simple, non-invasive and non-radioactive, etc. However, these current methods using by ultrasound technology such as diameter and collapsibility index of the inferior vena cava parameters cannot fully reflect the blood volume, the sensitivity and specificity of predicting hypotension after induction are not very satisfied. Recent reports have demonstrated that respirophasic variation in carotid artery blood flow peak velocity (ΔVpeak) and carotid corrected flow time (FTc) can noninvasively assess patient responsiveness to fluids. Thus, we speculate that the combined measurement of the parameters of the carotid artery and the inferior vena cava may more comprehensively and accurately assess the patient's blood volume status, thereby accurately predicting the occurrence of hypotension after induction of anesthesia.