M-mode ultrasonic localization of pleural effusion. Use in patients with nondiagnostic physical and roentgenographic examinations.

Fifty patients had nondiagnostic physical and roentgenographic examinations and were believed at high risk for exploratory thoracentesis. Negative echograms for pleural fluid were recorded for 13 patients. For 34 patients, the characteristic M-mode display of a central echo-free space, indicative of pleural fluid, was recorded. Aspiration yielded fluid that was localized by echography in 30 (88%). Of the 30 patients, 13 (43%) had normal lateral decubitus views, and 10 (33%) had experienced unsuccessful aspiration before ultrasound localized the fluid loculation. The remaining seven patients, including three receiving mechanical ventilation who were believed to have increased risk for thoracentesis had successful initial tap based on echographic localization of fluid. Ultrasound allows detection and localization of pleural fluid when roentgenographic and physical diagnostic means are not helpful.