Association between systemic immune-inflammation index and in-hospital mortality in ICU patients with aspiration...

BackgroundAspiration pneumonia is a common and life-threatening condition among critically ill patients, with mortality reaching 20-50%. The Systemic Immune-Inflammation Index (SII), derived from the routine complete blood count, has shown prognostic value in various inflammatory and infectious diseases, but its association with outcomes in ICU patients with aspiration pneumonia is unknown.ObjectivesTo investigate the association between SII and in-hospital mortality in ICU patients with aspiration pneumonia and to characterize the dose-response relationship.DesignRetrospective cohort study using a large publicly available critical care database.MethodsAdult patients (≥18 years) admitted to the ICU with aspiration pneumonia and an ICU stay ≥24 hours were identified in the MIMIC-IV database (version 3.1). SII (neutrophil × platelet/lymphocyte count) was derived from laboratory values obtained within the first 24 hours of admission and stratified into quartiles. Multivariable logistic regression with sequential adjustment evaluated the association with in-hospital mortality; restricted cubic splines characterized the dose-response relationship, and subgroup and sensitivity analyses assessed robustness.ResultsA total of 2,132 patients were included (median age 66 years, IQR 54-78; 62.2% male); overall in-hospital mortality was 25.5%. Mortality across SII quartiles was 24.6% (Q1), 20.5% (Q2), 26.1% (Q3) and 31.0% (Q4), exhibiting a U-shaped pattern. Using Q2 as reference, the highest quartile was independently associated with increased mortality (adjusted OR 1.53, 95% CI 1.14-2.06; P=0.005), and restricted cubic spline analysis confirmed a non-linear U-shaped relationship (P for trend = 0.003). Results were consistent after additional adjustment for vasopressor use and mechanical ventilation (adjusted OR 1.70, 95% CI 1.11-2.60; P=0.014) and across age, sex and comorbidity subgroups, with no significant interactions.ConclusionIn ICU patients with aspiration pneumonia, SII showed a U-shaped association with in-hospital mortality. Pending prospective and external validation, SII may represent a promising candidate biomarker for risk stratification.