Peripheral Perfusion Index: A narrative review for Emergency Physicians

The Peripheral Perfusion Index (PPI), derived from the photo-plethysmographic signal of pulse oximetry, provides a continuous, non-invasive assessment of peripheral microcirculatory perfusion, yet its diagnostic and prognostic potential in emergency care remains underrecognized To synthesize current evidence on the diagnostic and prognostic utility of PPI across prehospital and emergency department settings, clarify its relationship with established clinical and hemodynamic markers, and highlight practical considerations and research gaps for integrating PPI into routine emergency care PPI represents the ratio of pulsatile to non-pulsatile blood flow and is shaped by vascular tone, sympathetic activity, cardiac output, and local microcirculatory conditions. Emerging data show that it has substantial utility across multiple emergency care settings. In prehospital and ED cohorts, low PPI values are consistently associated with higher clinical acuity, occult shock, ICU admission, short-term mortality, transfusion requirements, fluid responsiveness, and adverse post–cardiac arrest outcomes. When tracked over time and interpreted alongside capillary refill time and macro-hemodynamic markers, PPI may even outperform tools such as the National Early Warning Score and shock index. Nevertheless, its interpretation is limited by interindividual variability, device-related differences, and physiological confounders, highlighting the need for standardized measurement protocols. PPI is an emerging perfusion biomarker that shows promise for early detection of hemodynamic compromise and for supporting triage and risk stratification in both emergency and prehospital settings. Future multicenter studies are required to refine clinically meaningful thresholds, evaluate PPI-guided resuscitation strategies, and embed PPI into decision-support algorithms for precision emergency care.