Vein size may predict blood pressure trouble in elderly surgery

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Age \> 60 years. * American Society of Anesthesiologists (ASA) physical state I-II. * Body mass index (BMI) ≤35 kg/m². Patients above this value will be excluded because obesity may cause technical difficulty and poor image quality in femoral vein ultrasound assessment. * Elective lower-limb orthopedic surgery under spinal anesthesia. Exclusion Criteria: * Patients refusing to participate. * History of psychiatric illness or seizures. * Absolute contraindications to spinal anesthesia: infection at the puncture site, severe coagulopathy/anticoagulation \[defined as platelet count \<75,000/µL, International Normalized Ratio (INR) \>1.5, Activated Partial Thromboplastin Time (aPTT) \>1.5 times control, or the use of anticoagulants such as warfarin, heparin, low molecular weight heparin, or direct oral anticoagulants within the recommended safety interval for neuraxial anesthesia\], severe hypovolemia, increased intracranial pressure, or known allergy to local anesthetics. * Severe cardiac disease, including left ventricular ejection fraction \<30%, Severe valvular heart disease (e.g., critical aortic stenosis), clinically significant arrhythmias (atrial fibrillation with uncontrolled ventricular rate \>120 bpm, frequent ventricular ectopy or sustained ventricular tachyarrhythmia) and congestive heart failure such as New York Heart Association (NYHA) class III-IV. * Severe uncontrolled hypertension, defined as persistent mean arterial pressure (MAP) ≥120 mmHg or systolic blood pressure (SBP) ≥180 mmHg and/or diastolic blood pressure (DBP) ≥110 mmHg despite medical therapy. * Severe respiratory diseases (Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage III-IV chronic obstructive pulmonary disease, or forced vital capacity (FVC) \<50% predicted). * Baseline bradycardia (\<50) or mean arterial blood pressure less than 60mmHg. * Emergency surgeries.