The prognostic nutritional index (PNI) and sepsis-induced cardiomyopathy (SCM) risk in the ICU: a retrospective study with L-shaped analysis

Background Sepsis-induced cardiomyopathy (SCM) is a common complication in patients with sepsis. Although the prognostic nutritional index (PNI) is less comprehensive than other assessment methods, it remains a readily accessible indicator of nutritional and immune status. This study aimed to investigate the relationship between SCM and the PNI. Methods This retrospective study included 200 septic patients admitted to the intensive care unit (ICU) at Linyi City People’s Hospital from 2023 to 2025. The primary endpoint was the occurrence of SCM during the ICU stay. Patients lacking essential variables (e.g., N-terminal pro-B-type natriuretic peptide NT-proBNP and ejection fraction EF) were excluded from the study. Missing data for other variables were imputed using multiple imputation methods. Restricted cubic spline (RCS) analysis and multivariate logistic regression analyses were performed to evaluate the relationship between SCM and the PNI. Subgroup analyses validated the robustness of the findings. Results SCM occurred in 63% of the study population, with incidence rates of 83.33, 61.19, and 44.78% in the T1 (PNI 31.3), T2 (31.3 ≤ PNI 38.65), and T3 (PNI ≥ 38.65) groups, respectively. A multivariate logistic regression analysis revealed a significant inverse association between the PNI and SCM (OR = 0.909, 95% CI: 0.862–0.955). Compared with the T1 group, the T3 and T2 groups had significantly lower SCM risks (OR = 0.162, 95% CI: 0.069–0.356; OR = 0.315, 95% CI: 0.135–0.700, respectively). The RCS analysis demonstrated an L-shaped relationship between the PNI and SCM risk, indicating a 10% reduction in risk per unit increase in PNI when the PNI was below 35. Subgroup analyses confirmed these results. Conclusion The PNI showed a negative, L-shaped association with the risk of SCM. These findings suggest that PNI can serve as an early risk stratification tool for SCM in septic patients, facilitating timely clinical intervention.