The goal of this Randomized controlled trial is to investigate the effect of shortening the duration of preoperative oral carbohydrate drinks on blood pressure after anesthesia induction in elderly patients undergoing joint replacement surgery. The main question it aims to answer is Whether preoperative oral carbohydrate drinks can reduce the incidence of hypotension after anesthesia-induced hypotension in elderly patients undergoing joint replacement surgery.According to the numerical table method, the patients in the experimental group will drink carbohydrate drinks the night before the operation and 3 hours before the operation, and the control group patients will routinely fast

Inclusion Criteria:

1. Patients undergoing elective unilateral joint replacement (total hip or knee)
2. ASAⅠ-Ⅲ

Exclusion Criteria:

1. Diagnosed patients at high risk of reflux aspiration (diabetes mellitus, obesity (BMI>30), gastrointestinal obstruction, elevated intracranial pressure, and esophageal disease)
2. Eating disorders
3. History of gastrointestinal or epigastric surgery
4. Recent use of drugs that affect gastrointestinal motility
5. Heart disease (severe arrhythmias, severe heart valve disease, heart failure, unstable angina on the day of surgery)
6. Severe poorly controlled hypertension (MAP≥135 mmHg) or hypotension (MAP≤55 mmHg) before induction
7. Difficult airway
8. Severe hepatic and renal insufficiency