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-tolarge 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 midaxillary 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 1cmin 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.