Endothelial Activation and Stress Index as an Indicator of Early Hemodynamic Instability in Critically Ill Patients: A Single-Centre Observational Study

Background: The Endothelial Activation and Stress Index (EASIX) is a biomarker initially developed to predict survival in patients with acute graft-versus-host disease after allogeneic haemato-poietic stem cell transplantation and is regarded as a surrogate of endothelial dysfunction. This study aimed to evaluate whether EASIX reflects early hemodynamic instability and vasopressor requirement in critically ill patients. Methods: We retrospectively analysed 447 patients admitted to the intensive care unit (ICU) at the University Clinical Centre in Gdańsk. Illness severity scores—including the Simplified Acute Physiology Score II (SAPS II), Acute Physiology and Chronic Health Evaluation II (APACHE II), and Sequential Organ Failure Assessment (SOFA)—and laboratory parameters, were collected at admission. EASIX, simplified EASIX (sEASIX), and modified EASIX (mEASIX) were calculated using established formulas. Vasopressor requirements, ex-pressed as norepinephrine equivalents (NEE), were recorded during the first 72 h. Statistical analyses included Spearman’s correlation, logistic regression, and receiver operating characteristic curve analysis. Results: In univariate analysis, EASIX was associated with ICU mortality (OR 1.333; 95% CI 1.135–1.576), but this association was not significant after adjustment. EASIX positively correlated with vasopressor requirements, severity scores (SOFA, SAPS II, APACHE II), and inflammatory and metabolic markers (PCT, CRP, lactate). It correlated with norepinephrine-equivalent doses within the first 48 h and moderately discriminated high-dose vaso-pressor use (>0.1 µg/kg/min). A weak negative correlation with ICU length of stay was observed. No association with age was found. Conclusions: EASIX is an age-independent marker associated with disease severity and early vaso-pressor burden in ICU patients. Rather than providing a direct measurement of endothelial function, it reflects a global signal of systemic stress and microvascular derangement and should be interpreted accordingly.