This study will compare two operating-room monitors-stroke volume variation (SVV, from the arterial line) and the Pleth Variability Index (PVI, from the pulse oximeter)-to see which one more accurately predicts whether giving a small fluid bolus will improve the heart's pumping during laparoscopic major abdominal surgery. Adults having elective surgery under general anesthesia will receive two small, timed 250-mL crystalloid infusions as part of routine care (one before and one after creation of the pneumoperitoneum). The research team will record SVV and PVI values just before and three minutes after each infusion while keeping these readings hidden from the clinicians so that usual care is not changed. No experimental drugs or devices are used. The main goal is to learn which index better identifies fluid responsiveness, so future care can be safer and more consistent. Potential risks are minimal and relate to the small fluid boluses (temporary changes in blood pressure or heart rate); the test stops if the anesthesiologist has any safety concerns. There is no direct benefit to participants, but results may help guide fluid therapy for similar patients in the future. The study is being conducted at a single academic hospital in the Republic of Korea and plans to enroll about 300 adults.