Patients aged 18-65 scheduled for elective laparoscopic cholecystectomy under general anesthesia will be included in the study. Exclusion criteria are as follows: Obesity (BMI > 35 kg/m²), presence of Atrial Fibrillation or serious cardiac arrhythmia, history of neck surgery or any pathology preventing internal jugular vein measurement, advanced heart failure (Ejection Fraction < 40%), severe valvular disease, peripheral vascular disease, emergency surgery, and refusal to participate in the study.
Upon arrival in the operating room, patients will be placed in a supine position. The Internal Jugular Vein (IJV) diameter will be monitored using a linear ultrasound probe during spontaneous breathing before anesthesia induction. The maximum and minimum diameters of the IJV during the respiratory cycle will be measured. The Internal Jugular Vein Collapsibility Index (IJV-CI) will be calculated using the following formula: [(IJV maximum diameter - IJV minimum diameter) / IJV maximum diameter] x 100.
Standard anesthesia induction will be performed. Non-invasive blood pressure and heart rate will be monitored and recorded at baseline (0 min), and at 1, 2, 3, 5, 7, 9, and 10 minutes following induction. Post-induction hypotension is defined as a decrease in mean arterial pressure (MAP) of more than 20% from the baseline value. The relationship between the pre-induction IJV-CI values and the development of hypotension during these specific time intervals will be statistically analyzed.