Advanced Emphysema Leads to High False Positivity Rate for Pneumothorax in Point of Care Ultrasound

Purpose: Point of Care Ultrasound (POCUS) is widely used to evaluate pleural apposition in acute disease; however, the prevalence of abnormal findings among emphysematous patients is unknown. The aim of the study was to characterize POCUS findings in advanced emphysema and correlate parenchymal and spirometric changes with abnormal POCUS results.

Materials and methods: We retrospectively evaluated POCUS images obtained in hyperinflated COPD patients. Images were obtained in the 2^nd intercostal space (upper lobes) and above diaphragm insertion (lower lobes). Pleural sliding was graded as "present" or "absent," and M-mode images graded as "seashore," "barcode," or "hybrid" patterns; patients were then assigned to four groups based on the combination of findings. Differences between pulmonary function testing and high-resolution CT were made by Chi Square or ANOVA testing, and association by Spearman's correlation. Agreement among three scorers (two pulmonologists and one radiologist) was assessed using Kappa statistics.

Results: Our study included 48 patients with 159 lobes imaged. We found a substantial percentage of lobes had either barcode M-mode appearance (13.8%) or indeterminate/absent lung sliding (20.3%). We identified 87 lobes (54.7%) that did not fit any typical definition for M-mode ultrasound findings. There was no strong association of abnormal ultrasound patterns with airflow obstruction or emphysema percentage. There was wide interrater variability among B-mode (0.20-0.611) and M-mode (0.24-0.049) among the three graders.

Conclusions: Hyperinflated patients often show abnormal pleural sliding appearance on POCUS, with a high false positive rate of barcode pattern. This should be considered when interpretation of POCUS drives therapeutic decisions.