Objective:To investigate the independent risk factors for postoperative severe pulmonary infection (SPI) in patients with severe traumatic brain injury (sTBI) and evaluate their predictive value.Methods:A retrospective cohort study was conducted to analyze the clinical data of 163 sTBI patients admitted to Tongji Hospital, Tongji Medical College of Huazhong University of Science and Technology from April 2021 and March 2023, including 101 males and 62 females, aged 20-80 years [53.0(46.0, 59.0)years]. The surgical procedures involved decompressive craniectomy, subdural hematoma removal, epidural hematoma removal, and intracranial hematoma removal. The patients were divided into SPI group ( n=62) and non-SPI group ( n=101) according to whether they had SPI postoperatively. The following data of the two groups were collected, including gender, age, preoperative Glasgow coma scale (GCS), elevated blood glucose, abnormal liver function, abnormal renal function, hemoglobin level, anemia, albumin level, hypoproteinemia, white blood cell count, neutrophil count, lymphocyte count, platelet count, neutrophil-to-lymphocyte ratio (NLR), derived neutrophil-to-lymphocyte ratio (dNLR), platelet-to-lymphocyte ratio (PLR), prognostic nutritional index (PNI) and serum lactate dehydrogenase (LDH) level. All the hematological tests were performed on venous blood samples collected preoperatively before anti-inflammatory treatment. Independent risk factors for predicting the postoperative occurrence of SPI in sTBI patients were identified through univariate analysis and multivariable stepwise regression analysis. The predictive value of separate indicator or indicators combined was assessed by calculating the area under the curve (AUC) of the receiver operating characteristic (ROC) curve. Results:Univariate analysis demonstrated that preoperative GCS, albumin level, lymphocyte count, NLR, PNI and serum LDH level in both groups were significantly correlated with the postoperative occurrence of SPI ( P<0.05), while gender, age, elevated blood glucose, abnormal liver function, abnormal renal function, hemoglobin level, anemia, hypoproteinemia, white blood cell count, neutrophil count, platelet count, dNLR and PLR were not correlated with the postoperative occurrence of SPI in sTBI patients ( P>0.05). Multivariable stepwise regression analysis revealed that low lymphocyte count (95% CI -0.337, -0.013, P<0.05), high NLR (95% CI -0.023, -0.005, P<0.01), low PNI (95% CI 0.007, 0.026, P<0.01), and high serum LDH (95% CI -0.002, -0.001, P<0.01) were independent risk factors for SPI in sTBI patients ( P<0.05). ROC curve analysis indicated that low lymphocyte count, high NLR, low PNI and high serum LDH level could predict SPI in sTBI patients postoperatively, with the combination of PNI and serum LDH showing the highest predictive ability (AUC=0.78, 95% CI 0.70, 0.85). Conclusion:Low lymphocyte count, high NLR, low PNI, and high serum LDH level are independent risk factors for postoperative SPI in patients with sTBI, and the combination of PNI and serum LDH possesses a high predictive value for postoperative SPI in sTBI patients.