Ultrasound of the Inferior Vena Cava in the Prevention of Hypotension After Induction of General Anesthesia

Inclusion Criteria: * Elderly patients undergoing elective non-cardiac surgery under general anesthesia; * Age 65-85 years old; * Body mass index (BMI) 18-28 kg/m2; * American society of anesthesiologists (ASA) class I-III. Exclusion Criteria: * Patient refusal or lack of cooperation; * Inability to communicate properly; * Severe sinus bradycardia, pacemaker implantation, atrioventricular block, and atrial fibrillation; * Presence of severe hepatic and renal function abnormalities; * Preoperative cardiac ultrasound suggesting LVEF \<50%; * Tricuspid valve displacement \<16 mm by preoperative cardiac ultrasound; * Chronic obstructive pulmonary disease; * Pulmonary hypertension; * Administration of drugs that inhibit the renin-angiotensin-aldosterone system; * Possibility of a difficult airway.