Measuring Pleural Effusion for Thoracentesis

Primary Measurement Technique

The American College of Critical Care Medicine recommends using bedside ultrasound to measure the maximal distance between parietal and visceral pleura at the thoracic base in the posterior axillary line during end-expiration, providing the most accurate volume estimation 1, 2

The American College of Critical Care Medicine recommends using ultrasound guidance for all thoracentesis procedures, particularly for small or loculated effusions, with a Grade 1B recommendation 1, 2
Ultrasound guidance decreases complications, such as pneumothorax, from 33-50% to 0% 1, 2
The success rate of obtaining fluid is 97% even after failed landmark-based attempts, according to the Thorax journal 3
The complication rate is 1.3% with ultrasound guidance versus 6.5% with landmark technique 1, 2

The Intensive Care Medicine journal recommends evaluating for internal echoes, septations, and loculations to distinguish simple from complex effusions before drainage 5
Septations are better visualized on ultrasound than CT scan, according to the Thorax journal 3

The Thorax journal recommends reserving contrast-enhanced CT for suspected malignant pleural disease or when delineating complex loculated effusions that are difficult to drain 3
CT should be performed before complete drainage, as pleural abnormalities are better visualized with fluid present 6

The Critical Care Medicine journal recommends not attempting thoracentesis for effusions <1 cm thickness on lateral decubitus view or ultrasound measurement 1, 2
Small effusions (<1 cm) require ultrasound guidance if drainage is clinically indicated, but ultrasound can successfully sample effusions as small as those visible only on imaging 1, 2