Ultrasonographic quantification of pleural effusion: comparison of four formulae

PURPOSE: The purpose of this study was to evaluate the correlations of ultrasonographically estimated volumes of pleural fluid with the actual effusion volume in order to determine the most reliable formula. METHODS: In 32 consecutive patients with clinically diagnosed pleural effusion, an ultrasound estimation was made of the volume of effusion using four different formulae, including two in the erect position and two in the supine position. Closed-tube thoracostomy drainage using a 28-Fr chest tube was performed. The total drainage was calculated after confirmation of full lung re-expansion and complete drainage by plain chest radiographs and ultrasound. The ultrasonographically estimated volume was compared to the actual total volume drained as the gold standard. RESULTS: There were 14 female and 18 male subjects. The mean age of all subjects was 41.56±18.34 years. Fifty percent of the effusions were in the left hemithorax. Metastatic disease accounted for the plurality of effusions (31.2%). The mean total volume drained for all the subjects was 2,770±1,841 mL. The ultrasonographically estimated volumes for the erect 1, erect 2, supine 1, and supine 2 formulae were 1,816±753 mL, 1,520±690 mL, 2,491±1,855 mL, and 1,393±787 mL, respectively. The Pearson correlation coefficients (r) for the estimate of each formula were 0.75, 0.81, 0.62, and 0.63, respectively. CONCLUSION: Although both erect formulae showed similar correlations, the erect 2 formula (Goecke 2) was most closely correlated with the actual volume drained.