The goal of this clinical trial is to learn about Whether carotid ultrasound guided fluid management can reduce the incidence of hypotension after general anesthesia induction in elderly patients undergoing gastrointestinal surgery.

The main question[s] it aims to answer are:

Whether fluid therapy reduces the incidence of general anaesthesia induced hypotension in elderly patients undergoing gastrointestinal surgery.

Whether carotid ultrasound can guide fluid management in elderly patients undergoing gastrointestinal surgery.

Participants will use carotid ultrasound to assess volume status. If volume is insufficient, fluid therapy will be selected until volume is sufficient, anesthesia will be then induced. If volume is sufficient, anesthesia will be directly induced. There is a comparison group: No carotid ultrasound will be used to assess the volume status of the patients, and anesthesia will be directly induced.

Inclusion Criteria:

• Age 60-80 years old
• gender unlimited
• ASA: Grade I-Ⅲ
• BMI:18-30kg/㎡
• Patients undergoing elective gastrointestinal surgery under general anesthesia Informed consent

Exclusion Criteria:

• Carotid artery stenosis ≥50%
• Patients with heart valve disease
• Patients with left ventricular ejection fraction < 50%
• Patients with cardiac dysfunction (NYHA grade Ⅲ-Ⅳ and/or NTproBNP≥900pg/ml)
• Patients Combined with renal insufficiency (creatinine ≥178μmol/L, and/or blood urea nitrogen > 9mmol/L)
• Preoperative systolic blood pressure> 160mmHg or diastolic blood pressure > 100mmHg
• Refuse to participate in the test
• Patients participating in other clinical trials

In this study, researchers and subjects were not blind. Anesthesiologists and data collectors were blind. Researchers conducted carotid ultrasound guided fluid therapy for experimental groups according to the groups, anesthesiologists performed routine induction for patients in the two groups, data collectors collected data, and anesthesiologists and data collectors did not know the groups of subjects.