Post-Thoracentesis Ultrasound versus Chest Radiography for the Evaluation of Effusion Evacuation and Lung Reexpansion: A Multicenter Study

Abstract

Rationale: Post-thoracentesis chest radiography (CXR) is often used to evaluate the degree of residual fluid after thoracentesis. Whether post-drainage ultrasound examination is comparable to CXR in the evaluation of pleural space evacuation is unknown. Objectives: 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 postprocedure; CXR was performed within 4 hours postprocedure. 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, midaxillary, 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 and 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 assessing complete pleural evacuation between ultrasound and CXR was 0.93 (95% confidence interval [CI], 0.83-1.00). When assessing agreement on the basis of 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 strong agreement (kappa = 0.81; 95% CI, 0.71-0.90) between proceduralist and blind ultrasound reviewers regarding complete pleural space evacuation. Conclusions: Post-thoracentesis ultrasound is an equally effective alternative to CXR in evaluating pleural space evacuation in simple pleural effusions.

Keywords: lung ultrasound; pleural effusion; thoracic radiology.

Figure 1.

Pre and postthoracentesis evaluation of pleural effusion using ultrasound and chest radiography (CXR). (A) Large free-flowing simple pleural effusion visible in the posterior view. (B, C) Effusion size measured in the anterior and midaxillary views. (D) Prethoracentesis CXR with a pleural effusion (arrow). (E–G) Post-thoracentesis images showing resolution of the effusion and complete pleural evacuation in the midaxillary, anterior, and posterior views. (H) Post-thoracentesis CXR with complete pleural evacuation.

Figure 2.

Forest plot showing hazard ratios and 95% confidence intervals (CIs) with variables considered in the univariate Cox proportional hazards model with nontrapped lung on ultrasound (US) as the dependent variable. Nontrapped lung was defined radiographically as lung apposition to the parietal pleura. Reference level for sex = “female”; US image = “anechoic,” etiology = “nonmalignant”. A P value <0.05 was considered statistically significant and an independent predictor of increased risk.