May the neutrophil-to-lymphocyte ratio at admission predict the occurrence and the severity of ARDS after blunt chest trauma patients? A retrospective study.

INTRODUCTION:In blunt chest trauma patients, the activation of inflammatory response is thought to be one of the pathophysiological pathways leading to delayed acute respiratory distress syndrome(ARDS). The main objective of the study was to assess the performance of the neutrophil-lymphocyte ratio(NLR) for prediction of delayed ARDS. The secondary objective was to compare NLR in patients with traumarelated focal and non-focal ARDS. METHODS:Over a 2-year period, every adult patient triaged to our level 1 trauma center with multiple rib fractures and PaO 2 /FiO 2 ratio > 200 at admission were retrospectively included. The NLR was recorded at admission in the Emergency Department(ED). The main study outcome was the occurrence of moderate to severe ARDS within 5 days after admission according to Berlin criteria. Two phenotypes (focal and non-focal ARDS) were determined based on the closest chest CT regarding the ARDS onset. RESULTS:216 patients were included and 42(19%) underwent moderate to severe ARDS within 5 days after ED admission (focal, N = 26 [12%] and non-focal, N = 16 [7%]). The NLR at ED admission was not statistically different between patients who developed or not a delayed ARDS (14 ± 13 vs. 11 ± 8,p = 0.095), although patients with non-focal ARDS presented higher NLR ratio than focal ARDS (21 ± 18 p < 0.0001). The AUC for NLR at ED in predicting delayed ARDS was 0.53. CONCLUSION:In blunt chest trauma patients, the NLR at ED admission was unable to predict delayed ARDS over the five first days post-injury. Although not clinically relevant, the NLR was higher in patients with non focal ARDS.