Depth of Pleural Effusion in Thoracentesis: Comparison of Lateral, Posterolateral and Posterior Approaches in the Supine Position

BACKGROUND In patients who have difficulty sitting, thoracentesis is attempted in a supine position via lateral approach. Recently, a new table has been designed for supine thoracentesis. This table has gaps that allow access to the posterolateral and posterior hemithorax. OBJECTIVES To compare important safety-related parameters between lateral, posterolateral, and posterior approaches in supine thoracentesis. MATERIALS AND METHODS First, two cadavers were placed supine on a table featuring gaps allowing access to the posterolateral and posterior hemithorax. Water was administered with sonographic measurement of the depth of pleural effusion (DPE) at the mid-axillary and posterior axillary line. Second, CT images were analyzed in 25 consecutive patients (32 free-shifting, moderate-to-large effusions; mean, 668 (146 - 2020 mL). DPE, craniocaudal distance that effusion can be visualized (CCD), and presence of passive atelectasis at each of the lateral, posterolateral, and posterior routes was assessed. RESULTS In each cadaver, DPE in the posterolateral route was greater than that in the lateral route (P = 0.002, P < 0.001). The amount of pleural fluid enough to spread DPE to higher than 1 cm at the posterior axillary line was less than half the amount at the mid-axillary line (500 mL vs. 1,100 mL; 800 mL vs. 1700 mL). CT showed that the DPEs and CCDs of posterolateral and posterior routes were greater than those of the lateral route (P < 0.001). In thirteen effusions (40.6%), DPE was greater than 1 cm in both posterolateral and posterior routes but less than 1 cm in the lateral route. Frequencies of passive atelectasis in posterolateral and posterior routes (81.3% and 90.6%) were higher (P < 0.001) than that in the lateral route (28.1%). CONCLUSION Safety-related parameters of posterolateral and posterior approaches in supine thoracentesis are far better than that of the conventional lateral approach.