This observational study investigates the predictors of Pleth Variability Index (PVI) changes in euvolemic patients undergoing laparoscopic-assisted vaginal hysterectomy (LAVH). The primary objective is to quantify changes in PVI (ΔPVI) across six intraoperative time points associated with positional shifts. Secondary objectives include identifying key predictors of significant PVI change (ΔPVI ≥ 5%), such as passive leg raising, Trendelenburg position, body mass index (BMI), and intraabdominal pressure. Additional variables including perfusion index, mean arterial pressure, bispectral index, skin temperature, age, and anesthetic agent will be evaluated as potential modulators. Findings aim to support individualized fluid management strategies in LAVH.

This prospective, single-center observational cohort study evaluates dynamic intraoperative changes in the Pleth Variability Index (PVI) in 50 adult female patients undergoing elective laparoscopically assisted vaginal hysterectomy (LAVH) at Wonkwang University Hospital.

After establishing euvolemia with a 500 mL Volulyte preload (Fresenius Kabi GmbH) over 30-50 minutes, no further intraoperative fluid boluses are given. Anesthesia is induced with propofol (2 mg/kg), fentanyl (1-2 μg/kg), and rocuronium (0.6 mg/kg), and maintained with sevoflurane or desflurane titrated to a bispectral index (BIS) of 40-60. Pneumoperitoneum is set at 12-15 mmHg, and positional maneuvers include 30° passive leg raising, 15° Trendelenburg, and 15° reverse Trendelenburg.

Monitoring devices and data acquisition:

• **Masimo Radical-7** pulse oximeter (PVI, perfusion index [PI])
• **Invasive arterial line** (mean arterial pressure [MAP])
• **BIS sensor** (BIS)
• **Skin temperature probe** (forearm, °C) calibrated pre-case

Measurements are recorded at six standardized time points (baseline; post-induction; post-passive leg raising; post-pneumoperitoneum; post-Trendelenburg; post-reverse Trendelenburg). Continuous waveforms are averaged over 30 s epochs.

Primary endpoint is the absolute change in PVI (ΔPVI) relative to baseline. Secondary analyses include:

• Multivariable logistic regression for predictors of ΔPVI ≥ 5%
• Multivariable linear regression for continuous ΔPVI prediction
• Correlation analyses of ΔPVI with intraabdominal pressure (mmHg) and body mass index (kg/m²)
• Sensitivity analysis of PI reliability (intraclass correlation coefficient) across skin temperature thresholds
• Descriptive statistics for frequency of vasopressor (ephedrine) use

All analyses are performed using SPSS v29.0 with p < 0.05 considered statistically significant (Bonferroni correction applied for repeated measures).

Inclusion Criteria:

• adult females aged 19-70 years (American Society of Anesthesiologists physical status I-III) scheduled for elective LAVH.

Exclusion Criteria:

• emergency surgery, severe cardiac or pulmonary disease, renal failure, pregnancy, or conditions contraindicating fluid administration. Participants were consecutively recruited during preoperative consultations.

Adult female patients aged 19 to 70 years with ASA physical status I-III who are scheduled to undergo elective laparoscopic-assisted vaginal hysterectomy (LAVH) at Wonkwang University Hospital. All participants are screened during routine preoperative consultations and provide written informed consent prior to enrollment.