Ultrasound findings
The LUS findings of our patients were as follows: subpleural consolidation in 70 (72.8%) patients, confluent B-lines in 19 (19.8%) patients, focal multiple B-lines in 4 (4.1%) patients, and pleural effusion in 3 (3.1%) patients. Table 1 shows the M-mode sonographic findings of diaphragm thickness, TF, diaphragm excursion, IS, ES, and total duration time of the respiratory cycle of the patients enrolled in the study. Values of IS and ES were found to have significant positive correlations with respiratory rate and length of stay in hospital and negative correlations with SpO2 levels evaluated at the time of admission to the emergency department. (Table 2). Additionally, TF values were negatively correlated with respiratory rate (p : 0.022, r : -0.236) and length of stay in the emergency department (p : 0.016, r : -0.256).
In order to obtain homogeneous numbers of patients in the clinical severity groups, patients in the groups of PRESS grades 0–1 and grades 4–5 were merged, so four groups were evaluated for clinical severity scores as follows: PRESS scores 0–1, 2, 3, and 4–5. The IS and ES values differed significantly between these four groups; patients with higher clinical scores had increased IS and ES values (p <0.001) (Graphic 1). There was a positive correlation between the clinical score and IS (p <0.01,r :0.541) and ES (p <0.01, r :0.429). Thickening fraction values were also significantly different between groups; patients with higher clinical scores had lower TF values (p : 0.001) (Table 3, Graphic 2), and there was a negative correlation between TF and clinical score (p <0.01,r : -0.318). Although there was no statistically significant difference, diaphragm excursion was higher in the severe group (PRESS 4–5) than the mild and moderate (PRESS 0–3) group (2.2±0.56 vs. 2.2±0.59). Patients who required respiratory support (HFNC or BiPAP therapy) had higher IS and ES measurements (p : 001, p : 0.004).
Analysis of ROC curves was performed and the value of the area under the curve (AUC) for IS among patients of PRESS grades 4 and 5 was found to be 0.805 (95% confidence interval (CI): 0.670–0.910). At a cut-off level of 0.277 cm/s, the sensitivity and specificity of IS values for PRESS grades 4 and 5 were 87.5% and 51.9%. For ES, the AUC value among patients of PRESS grades 4 and 5 was 0.761 (95% CI: 0.650–0.890). At a cut-off level of 0.248 cm/s, the sensitivity and specificity of ES values for PRESS grades 4 and 5 were 87.5% and 58.2%, respectively (Figure 2).