Total arterial impedance (Ztot) is an advanced hemodynamic parameter that reflects the global arterial load opposing ventricular ejection by integrating both steady and pulsatile components of the arterial system. Although Ztot can be continuously derived from Pressure Recording Analytical Method (PRAM)-based monitoring, physiological reference values under stable clinical conditions are not well established.

This observational study aims to define patient-level physiological reference values for Ztot using intraoperative hemodynamic data obtained from PRAM-based arterial waveform analysis during hemodynamically stable periods. In addition, the study evaluates the associations between Ztot and key hemodynamic variables reflecting arterial load and cardiovascular performance.

High-resolution intraoperative data routinely recorded during standard clinical care are retrospectively analyzed. The findings of this study are intended to improve the interpretability of Ztot in advanced hemodynamic monitoring and to support future clinical and research applications.

Total arterial impedance (Ztot) is a comprehensive descriptor of arterial load that integrates resistive, compliant, and pulsatile components of the arterial system. Unlike conventional pressure-based parameters, Ztot provides a more physiologically meaningful representation of the opposition encountered by ventricular ejection. Although Ztot can be continuously estimated using Pressure Recording Analytical Method (PRAM)-based arterial waveform analysis, standardized physiological reference values applicable to routine clinical practice are lacking.

This single-center, observational study is designed to establish patient-level reference values for PRAM-derived Ztot during hemodynamically stable intraoperative periods. The study retrospectively analyzes high-resolution intraoperative hemodynamic data obtained during routine clinical care. Adult surgical patients monitored with an invasive arterial catheter and PRAM-based hemodynamic monitoring are included in the analysis.

Hemodynamic stability is defined according to predefined physiological criteria, including ranges of mean arterial pressure, cardiac index, heart rate, stroke volume variation, cardiac cycle efficiency, and arterial waveform quality indicators. Only measurements meeting all stability criteria are considered eligible for analysis.

To account for repeated measurements within individuals, patient-level median values are used for all primary analyses. The physiological reference interval for Ztot is estimated using a non-parametric percentile-based approach. In addition, associations between Ztot and key hemodynamic variables related to arterial load and cardiovascular performance are explored using correlation analyses.

This study does not involve any interventions, treatment assignments, or changes to standard clinical management. The primary objective is descriptive and physiological, aiming to provide a reference framework that may enhance the clinical interpretability of Ztot in advanced hemodynamic monitoring. The results are expected to support future prospective and outcome-oriented research evaluating the role of Ztot in perioperative and critical care settings.

Inclusion Criteria:

• Adult patients (≥18 years) who underwent surgery with invasive arterial catheterization.
• Availability of intraoperative hemodynamic data recorded using PRAM-based arterial waveform monitoring.
• Presence of predefined hemodynamically stable intraoperative periods meeting physiological stability criteria.
• Adequate arterial waveform signal quality for PRAM-derived parameter analysis.

Exclusion Criteria:

• Age <18 years.
• Inadequate arterial waveform signal quality or missing PRAM-derived data.
• Absence of intraoperative periods fulfilling predefined hemodynamic stability criteria.
• Incomplete or corrupted intraoperative monitoring records.

The study population consists of adult surgical patients who underwent routine intraoperative invasive arterial monitoring, from whom PRAM-based hemodynamic data were retrospectively analyzed during predefined hemodynamically stable intraoperative periods.

Individual participant data will not be shared due to institutional and ethical restrictions related to patient privacy and the retrospective nature of the study. The analyzed data consist of anonymized intraoperative monitoring records collected during routine clinical care. Aggregated and summary-level results are reported in publications, and additional information may be made available upon reasonable request and with appropriate institutional approval.