Post-thoracentesis Ultrasound vs. Chest X-ray for the Evaluation of Effusion Evacuation and Lung Re-Expansion, A Multicenter Study.

Introduction: Post-thoracentesis chest radiography (CXR) is often used to evaluate the degree of residual fluid post-thoracentesis. Whether post-drainage ultrasound exam is comparable to CXR in the evaluation of pleural space evacuation is unknown.

Research question: How do post-thoracentesis ultrasound and CXR compare in assessing the effectiveness of pleural space evacuation?

Methods: In this prospective, multicenter study, patients with free-flowing pleural effusions with minimal to no septations requiring thoracentesis were recruited. Post-thoracentesis ultrasound was performed immediately post-procedure; CXR was performed within 4-hours post-procedure. The primary outcome was agreement on complete pleural space evacuation between ultrasound and CXR. Complete pleural space evacuation was defined as the absence of pleural fluid on anterior, mid-axillary, and posterior ultrasound views and lack of costophrenic angle blunting on CXR. Interobserver reliability was assessed via independent image reviews by two pulmonologists and two radiologists blinded to patient/procedure data, with disagreements resolved by a third reviewer.

Results: Of the 147 patients enrolled (February/2021 - May/2022), 145 were included in the final analysis. The median age was 64 years (56-75), and malignancy was the most frequent effusion etiology (n=49). The lung was considered trapped in 50% (n=73). A total of 826 ultrasound images were collected for blind review. The Gwet's Agreement Coefficient 1 (AC1) assessing complete pleural evacuation between ultrasound and CXR was 0.93 (95% CI: 0.83-1.00). When assessing agreement based on the pre-specified criteria of effusion size (small vs large), a substantial level of agreement was observed between ultrasound and CXR, indicated by a kappa of 0.64 (95% CI: 0.51-0.77). There was a strong agreement (kappa= 0.81 (95% CI: 0.71-0.90)) between proceduralist and blind ultrasound reviewers regarding complete pleural space evacuation.

Conclusion: Post-thoracentesis ultrasound is an equally effective alternative to CXR in evaluating pleural space evacuation in simple pleural effusions.