Relationship Between Systemic Immune‐Inflammation Index and In‐Hospital Mortality in Sepsis Combined With Chronic Obstructive Pulmonary Disease Modified by Mechanical Ventilation

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.