Determination of the ED50 and ED95 of Prophylactic Norepinephrine Infusion for Preventing Post-induction Hypotension in Elderly Patients Undergoing Major Abdominal Surgery

Second Affiliated Hosptial， School of Medicine, ZheJiang University

The goal of this clinical trial is to determine the ED50 and ED95 of prophylactic norepinephrine infusion for preventing post-induction hypotension in elderly patients undergoing major abdominal surgery using up-and-down sequential method . The main question it aims to answer is:

What is the effective concentration of prophylactic norepinephrine infusion for preventing post-induction hypotension in elderly patients.

Participants will receive different concentrations of norepinephrine infusion at the beginning of anesthesia induction until 15 minutes after intubation.

Inclusion Criteria:

• aged 65 to 80 years
• Undergoing major abdominal surgery
• American Society of Anesthesiologists (ASA) physical status of I/II/III

Exclusion Criteria:

• Patient refusal
• Severe untreated or uncontrolled hypertension despite medications
• Bradycardia (heart rate < 50 beat per minute)
• Cardiac morbidities, heart block greater than the first degree
• Severe hepatic and renal dysfunction
• hyperthyroidism
• vascular diseases
• BMI>30
• Monoamine oxidase inhibitors were used 2 weeks before surgery