To explore the prediction value of alveolar lavage fluid Simpson's diversity index (SDI) and serum procalcitonin (PCT) in bacterial pneumonia patients with mechanical ventilation.

The clinical data of 64 patients with bacterial pneumonia who received mechanical ventilation and metagenomic next-generation sequencing technology in the ICU of the Affiliated Hospital of Yangzhou University from June 2019 to June 2021 were collected in this study. According to the 28-day outcome, all patients were divided into a survival group (44 cases) and a death group (20 cases). The acute physiology and chronic health evaluation (APACHE) Ⅱ score, SDI and PCT were collected within 24 h after admission to ICU. Spearman analysis was used to analyze the correlation between SDI and PCT. The Logistic regression model was established to analyze risk factors affecting the prognosis of bacterial pneumonia patients with mechanical ventilation, and the receiver operating characteristic (ROC) curve was drawn to evaluate the predictive value of SDI and PCT.

The APACHEⅡ score [(14.6 ± 1.8) vs. (18.4 ± 1.9), t = 7.716, P < 0.001] and PCT level [(4.6 ± 2.1) μg/L vs. (9.0 ± 2.1) μg/L, t = 7.869, P < 0.001] in the survival group were much lower than those in the death group, while the SDI level [0.50 (0.44, 0.64) vs. 0.29 (0.25, 0.32), Z = 5.579, P < 0.001] in the survival group was much higher. The correlation analysis showed that SDI was negatively correlated with PCT (r = -0.810, P < 0.001). Binary Logistic regression analysis showed that SDI was the protective factor and PCT was the risk factor for death in bacterial pneumonia patients with mechanical ventilation (both P < 0.05). ROC curve analysis showed that the area under the ROC curve (AUC) for predicting the 28-day prognosis of bacterial pneumonia patients with mechanical ventilation was 0.937 for SDI, 0.931 for PCT and 0.950 for SDI combined with PCT. The AUC of SDI combined with PCT was much higher than that of PCT (Z = 1.892, P = 0.043).

Both SDI and PCT have high diagnostic value for the prognosis of bacterial pneumonia patients with mechanical ventilation, and SDI combined with PCT has better predictive value.