Trial intervention
NE Group: From 10 min after anesthesia induction to the end of surgery, a micro-injection pump was utilized to intravenously inject norepinephrine at a rate of 0.05–0.1 mg/(kg·min), which raises and stabilizes the mean arterial pressure at 80–90 mmHg. A NE solution was prepared by diluting 2 mg NE in 50 ml of physiological saline.C Group: From 10 min after anesthesia induction to the end of surgery, an intravenous injection of the same amount of physiological saline as the placebo was administered through a pump, and additional adjustments to blood pressure were not made during the operation.