Abstract
INTRODUCTION: This retrospective cross-sectional study examined the correlation between Systemic Immune-Inflammation Index (SII) and in-hospital mortality in patients with sepsis combined with chronic obstructive pulmonary disease (COPD) and explored the modifying effect of mechanical ventilation on this relationship. METHODS: Logistic regression models were employed to explore the correlation between log SII and in-hospital mortality. The receiver operating characteristic curve and decision curve analysis were used to examine the predictive value of log SII for in-hospital mortality. Generalized linear regression analysis, logistic regression analysis, and restricted cubic spline were used to explore the associations among log SII, in-hospital mortality, and mechanical ventilation states. RESULTS: A total of 1058 patients were enrolled. Log SII was an independent risk factor for in-hospital mortality in patients with sepsis combined with COPD (odds ratios for Model 1, Model 2, Model 3, and Model 4 were 3.116, 2.847, 2.244, and 3.495, respectively; p < 0.005; log SII as an optimal-threshold categorical variable). Additionally, mechanical ventilation was closely related to log SII (p < 0.05). There was a stronger correlation between log SII and in-hospital mortality of patients who received mechanical ventilation, especially those with invasive mechanical ventilation (p < 0.05). CONCLUSION: An elevated SII independently predicts elevated in-hospital mortality risk in sepsis-COPD patients. This association is strongly intensified by mechanical ventilation, particularly the invasive mode. SII serves as a valuable biomarker for risk stratification in this vulnerable population.