Study on risk factors and interaction effects of delirium in patients with severe pneumonia in intensive care unit

Abstract

BACKGROUND

Delirium is a common and serious complication in the intensive care unit (ICU). Its occurrence not only aggravates the original condition but also prolongs mechanical ventilation and hospitalization, and is closely associated with a poor prognosis. We hypothesized that delirium in patients with severe pneumonia in the ICU is not determined by a single factor but by multiple identifiable clinical risk factors and their interaction effects.

AIM

To explore the risk factors and interaction effects of delirium in patients with severe pneumonia in the ICU.

METHODS

A total of 274 patients with severe pneumonia admitted to Beijing Shijitan Hospital, Capital Medical University, between January 2024 and June 2025 were selected. Depending on whether delirium occurred during the ICU stay, the patients were divided into a delirium group (71 cases) and a non-delirium group (203 cases). The risk factors for postoperative delirium were analyzed using logistic regression analysis. Multi-factor dimensionality reduction was used to analyze the interactions between risk factors.

RESULTS

Significant differences in diabetes (P = 0.003), mechanical ventilation time (191.09 ± 43.75 hours vs 136.74 ± 40.92 hours, P < 0.001), blood lactic acid (5.14 ± 1.55 mmol/L vs 2.91 ± 0.74 mmol/L, P < 0.001), blood calcium (2.23 ± 0.15 mmol/L vs 2.36 ± 0.09 mmol/L, P < 0.001), arterial oxygen saturation (P = 0.001), and Acute Physiology and Chronic Health Evaluation II (APACHE II) score (P < 0.001) were observed between the two groups. Mechanical ventilation time [1.029 (1.015-1.044), P < 0.001], blood lactic acid [5.229 (3.017-9.062), P < 0.001] and APACHE II scores [3.368 (1.227-9.246), P = 0.018] were risk factors for delirium in ICU patients with severe pneumonia (all P < 0.05). A significant interaction was found among diabetes, arterial oxygen saturation, and APACHE II score (P < 0.001). The area under the receiver operating characteristic curve (AUC) of the regression model with an interaction effect was 0.531 (P = 0.431). The AUC of the model without an adjusted interaction effect was 0.958 (P < 0.001).

CONCLUSION

Mechanical ventilation time, blood lactic acid, and APACHE II score are delirium risk factors. The interaction among diabetes, arterial oxygen saturation, and APACHE II score may predict delirium.

Keywords: Severe pneumonia; Delirium; Risk factors; Interactions; Multi-factor dimensionality reduction

Core Tip: The results of this study show that delirium affects 25.91% of intensive care unit patients with severe pneumonia. Prolonged mechanical ventilation, elevated blood lactate levels, and higher Acute Physiology and Chronic Health Evaluation II (APACHE II) scores are independent risk factors for delirium development. Notably, diabetes, arterial oxygen saturation, and APACHE II score demonstrate significant three-way interaction effects, suggesting that delirium results from complex synergistic pathophysiological processes. Early identification of high-risk patients using these combined indicators may enable targeted preventive interventions, ultimately improving clinical outcomes in this vulnerable population.