Association Between Intraoperative Perfusion Index and Mortality in Patients Undergoing General Anesthesia for Noncardiac Surgery: A Protocol for an Observational Study

Background: Hemodynamic derangement during general anesthesia is associated with postoperative morbidity and mortality. Current paradigms for hemodynamic management focus on optimizing macrocirculatory parameters, which may not adequately reflect or improve microcirculatory function. The peripheral perfusion index, a noninvasive measure derived from pulse oximetry, may provide an indication of tissue perfusion status. In smaller studies, the intraoperative perfusion index has been linked to postoperative complications and mortality. This retrospective cohort study will evaluate the association between intraoperative perfusion index and postoperative outcome. We hypothesize that increasing duration of low intraoperative perfusion index is associated with higher postoperative morbidity and mortality. Methods: We will conduct a retrospective cohort study including all adult patients who underwent general anesthesia for noncardiac surgery in the Capital and Zealand Regions of Denmark between 2017 and 2024. Patients will be identified through the AI and Automation in Anesthesia perioperative database, which contains granular perioperative data for all surgical procedures in this period. The primary exposure is intraoperative perfusion index, analyzed both as a continuous variable and as the area under predefined thresholds (1.5, 0.5, and 2.0). The primary outcome is 30-day all-cause mortality and the secondary outcome is a composite of postoperative complications. Associations between intraoperative perfusion index and outcomes will be evaluated using adjusted multivariable logistic regression with restricted cubic splines. Ethics and Dissemination: The Regional Health Research Ethics Committees of the Capital Region in Denmark waived the requirement for formal ethical approval of this study (F-24078050, December 12, 2024), as the study will use data exclusively from existing medical records. Results will be disseminated through peer-reviewed publication and conference presentations and reported in accordance with the STROBE guidelines.