Internal Jugular Venous Distensibility Index and Innominate Venous Flow Patterns As Predictors of Fluid Responsiveness

Inclusion Criteria: 1. Utilizing intraoperative mechanical ventilation with a tidal volume of 8 ml/kg (PBW). 2. ASA physical status 1-3. 3. Mongoloid ethnicity. 4. Willing to participate in the research and sign the informed consent. Exclusion Criteria: 1. Patients with symptoms and signs of fluid overload, such as pulmonary edema, pleural effusion, ascites, and peripheral edema. 2. Patients with chronic or acute kidney dysfunction, renal replacement therapy history, and/or oliguria (urine output \<0.5 ml/kg/hour). 3. Patients with cardiovascular diseases, including heart failure, cardiac arrhythmias, moderate-to-severe valvular abnormalities, a history of angina/myocardial infarction, pulmonary hypertension, and peripheral artery disease. 4. Patients with anatomical abnormalities in the neck and chest region that make it impractical to perform jugular vein ultrasound and transthoracic echocardiography. 5. Jugular vein thrombosis. 6. Superior vena cava syndrome. 7. Placement of jugular vein catheter. 8. Body mass index (BMI) greater than 30.0 kg/m2. 9. Patients with contraindications to the use of muscle relaxants. 10. Patients with lung hyperinflation and pleural effusion. Drop out criteria: 1. Patients who wish to withdraw from the study. 2. Post-anesthesia induction complications and emergencies. 3. Transthoracic echocardiography provides a less representative image due to difficult acoustic window.