A total of 338 patients with AEP were evaluated. Table 1 shows the general clinical characteristics of the patients. All but one patient was male (99.7%), and their mean age was 20.4 years. Only two patients were never smokers. Mean total number of cigarette smoking days was 26.2. Mean WBC level was 14,359. Mean PEC, BEP, and CRP levels were 4.1%, 46.7%, and 9.4, respectively. About 37% of patients were initially admitted to the ICU, and mean hospital days, ICU admission days, and oxygen supply days were 10.5, 2.0, and 2.8, respectively. Three patients underwent mechanical ventilation and nine patients were oxygenated with HFNC during ICU care. The initial chest radiograph findings revealed 94.1% bilateral infiltrates and 51.2% bilateral effusion. As an initial treatment, 76.9% of patients underwent intravenous corticosteroid therapy, 18.9% underwent oral corticosteroid therapy, and 4.1% did not receive steroids. The mean duration of steroid treatment was 14.2 days.
Correlation between BEP and other significant parameters
BEP had a linear increasing relationship with the PaO2/FiO2 ratio (Pearson’s correlation coefficient r = 0.207, P = 0.008) (Fig. 1A). In addition, the number of oxygen supply days had a linearly decreasing relationship with BEP (Pearson’s correlation coefficient r = –0.202, P = 0.005) (Fig 1B). PEC had a linearly increasing relationship with BEP (Pearson’s correlation coefficient r = 0.276, P < 0.001) (Fig. 1C) and a linearly decreasing relationship with the number of oxygen supply days (Pearson’s correlation coefficient r = –0.157, P = 0.014) (Fig. 1D).
Comparison between groups stratified by the BBE score
A total of 244 patients had both an initial complete blood count and BAL results for evaluation. The cut-off of BEP was calculated using ROC curve analyses. The area under the ROC curve was 0.577 with a P-value of 0.04. The calculated cut-off was 41.5 for BEP.
The baseline clinical characteristics of the 244 patients are shown in Table 2. Mean WBC, PEC, BEP, and CRP were 14,231, 3.8%, 46.8%, and 9.5, respectively. The mean number of hospital days was 11.0 and ICU admission days was 2.0. The mean PaO2/FiO2 ratio at admission was 261.9. After stratification by BBE score, 78 patients were in group with score 0, 108 patients were in group with score 1, and 58 were in group with score 2. Male proportion and mean age were not different between the groups. The proportion of ever smokers and the mean number of smoking days were not significantly different.
WBCs were significantly different between the groups. The mean WBC decreased with an increase in the BBE score. The values were 16,248, 14,489, and 11,037 for groups with score 0, 1, and 2, respectively (P < 0.001). Both mean PEC and BEP increased significantly as the score increased from 0 to 2 (P < 0.001 and P < 0.001, respectively). CRP was inversely related with the score (P < 0.001). The mean number of hospital days decreased significantly as the score increased from 0 to 2 (P = 0.009) (Fig. 2A). The proportion of patients who were admitted to the ICU was significantly lower in group with score 2 than in group with score 0 (P < 0.001). The mean duration of ICU stay was not significantly different between the groups (P = 0.731).
A higher proportion of patients was given additional oxygen as the score decreased from 2 to 0 (P = 0.031). Two patients in group with score 0 and 1 patient in group with score 1 were mechanically ventilated, but no one in group with score 2 underwent mechanical ventilation. The mean total number of days of oxygen supply was 3.4, 2.8, and 2.3 in groups with score 0, 1, and 2, respectively (P = 0.002) (Fig. 2B), while the mean number of steroid treatment days was 15.5, 14.0, and 12.6, respectively (P = 0.006). The initial PaO2/FiO2 ratios were 249.7, 253.8, and 300.9, respectively (P = 0.003) (Fig. 2C).
Association with significant oxygen requirements
Age, CRP, smoking duration before admission, BEP, PEC, and BBE score were entered into univariate analyses to determine the association with significant oxygen requirements. CRP, BEP (categorical), PEC, and BBE scoring were significant in univariate analyses. Two models were applied for multivariate analyses. In model 1, BBE scoring was entered, while BEP and PEC were excluded. In model 2, BEP and PEC were included, while BBE score was excluded. In model 1, BBE score was the only significant factor associated with significant oxygen requirements (P = 0.018). Compared to group with score 2, the odds ratio (OR) for significant oxygen requirements was 2.25 (95% confidence interval [CI]. 1.112–4.574, P = 0.024) for group with score 1, while the OR was 3.014 (95% CI 1.378–6.593, P = 0.006) for group with score 2. In model 2, BEP was a significant factor (OR 1.939, 95% CI 1.072–3.505, P = 0.028).