Impact of pleural manometry in predicting non-expandable lung: a prospective study

Abstract Background Pleural manometry provides a real-time assessment of pleural pressure during thoracentesis and may aid in identifying non-expandable lung (NEL). Its diagnostic value relative to conventional pleural fluid biomarkers remains unclear. Objective To evaluate the diagnostic performance of pleural manometry in predicting non-expandable lung and to compare it with standard pleural fluid biochemical markers. Methods In this prospective observational study, 90 adults with pleural effusion undergoing therapeutic thoracentesis were enrolled. Pleural pressure was measured using a hemodynamic transducer during stepwise fluid removal. Pleural elastance (Pel) was calculated as the change in pleural pressure per unit volume removed. Lung expandability was determined based on post-procedure clinical and radiological assessment. Diagnostic performance was assessed using logistic regression and receiver operating characteristic (ROC) curve analysis. Results Non-expandable lung was identified in 35.6% of the studied patients. Pleural elastance showed excellent diagnostic accuracy (AUC = 0.970, p < 0.001). A cutoff value of ≤ 14 cmH₂O/L predicted lung expandability with 98.3% sensitivity and 96.9% specificity. In contrast, pleural fluid biomarkers demonstrated moderate performance (AUC range: 0.759–0.848). Higher elastance values and more negative closing pressures were significantly associated with non-expandable lung and symptom development during thoracentesis. Conclusion Pleural elastance is a highly accurate and clinically useful predictor of lung expandability, outperforming conventional biochemical markers. Routine use of pleural manometry during thoracentesis may enhance procedural safety and support early identification of non-expandable lung.