2.3 Statistical methods
The Kolmogorov-Smirnov method was used to test the normal distribution. The rank sum test was used to analyze the difference in continuous variables that are in non-normal distribution. The chi-square test was used to analyze the difference in classified variables. The variables with statistical differences were included in multivariate logistics regression analysis. When P < 0.05, the differences were considered to be statistically significant. The statistical software was SPSS24.0.
3 Results
A total of 194 cases of TFBA were included in this study, 120 males and 74 females with a median age of 1.54 years (0.6-12.58 years). The types of TFBA were inorganic (n = 7), other organic (n = 33), nuts (n = 143) and legumes (n = 11). Cervicothoracic CT showed TFBA embedded in trachea and above trachea in 24 cases, in left and right main bronchus in 134 cases (left bronchus 87 cases, right bronchus 47 cases), in segmental bronchus and below in 36 cases (left segmental bronchus 6 cases, right segmental bronchus 30 cases). Cervicothoracic CT showed no obvious abnormality in 60 cases, obstructive emphysema or atelectasis in 77 cases, obstructive pneumonia 50 cases, and the rest 7 cases (pleural effusion, mediastinal displacement, subcutaneous emphysema, pneumothorax and mediastinal emphysema). The general characteristics are showed in Table 1.
We conducted a univariate analysis on risk factors mentioned in previous literature and clinically considered possible. The results showed that there was a significant difference in cervicothoracic CT diagnosis and the retention time of TFBA between LRTI group and non-LRTI group. The results of univariate analysis are showed in Table 2.
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Cervicothoracic CT diagnosis and the retention time of TFBA were included in multivariate logistics regression analysis. We found that there was a correlation between the retention time of TFBA and LRTI, while no correlation was found between cervicothoracic CT diagnosis and LRTI. The results of multivariate logistics analysis are showed in Table 3.