The investigators aimed to investigate the effects of continuous infusion of norepinephrine before and after general anesthesia induction on the occurrence of post-induction hypotension.

Intraoperative hypotension is common after general anesthesia induction and is associated with adverse postoperative events. Norepinephrine is one of the most applied vasopressors in clinical to treat intraoperative hypotension. Due to the absence of effective measures for predicting intraoperative hypotension, infusing norepinephrine before and during anesthesia induction may reduce intraoperative hypotension. There is currently a lack of research regarding whether continuous norepinephrine infusion before and during the induction of general anesthesia can mitigate or prevent post-induction hypotension. The investigators aim to investigate the effects of continuous infusion of norepinephrine before and after general anesthesia induction on the occurrence of post-induction hypotension.

Inclusion Criteria:

• Patients aged above 65 years or those above 45 years with at least one of the following preoperative cardiovascular diseases: essential hypertension, coronary artery disease, stroke, or type I/II diabetes mellitus.
• Patients who will receive major noncardiac surgery as open or laparoscopic abdominal surgeries with an anticipated operative duration over two hours, including gastrointestinal, liver, pancreatic, bladder, and uterine/adnexal surgeries.

Exclusion Criteria:

• Patients who declined to participate in the present study.
• Patients enrolled in another ongoing clinical study.
• Patients with systolic arterial pressure (SAP) below 90 mmHg or above 160 mmHg, or heart rate (HR) over 100 beats per minute (bpm) before anesthesia induction.
• Patients who have experienced any type of shock within 30 days before surgery.
• Patients with circulatory instability require continuous or intermittent positive inotropic and/or vasopressors within 24 hours before surgery.
• Patients receive continuous or intermittent intravenous antihypertensive agents within 24 hours before surgery.
• Patients underwent coronary artery bypass grafting, coronary angiography, or coronary stenting within 180 days before surgery.
• Patients who were diagnosed with new-onset tachyarrhythmia within 180 days before surgery, such as atrial fibrillation, atrial flutter, and premature ventricular contractions.
• Patients with preoperative alanine aminotransferase >80 international units and/or glomerular filtration rate < 80 ml/min within the 180 days before surgery.
• Patients are ineligible for intraoperative invasive radial artery blood pressure monitoring.
• Patients with a known history of allergy to norepinephrine.
• Patients who were planned for rapid sequence induction.
• Patients who were scheduled for awake tracheal intubation.
• Patients who were scheduled for double-lumen endotracheal intubation. Pregnant or lactating patients.