The aim of this study was to quantify the volume of pleural effusions (PEs) in the critically ill using ultrasound. PE was suggested on the daily postero-anterior chest radiography [1] in the semirecumbent position. All patients with suspected PE were investigated with ultrasound. We hypothesize that there is a strong correlation between the maximal width of the fluid lamella along the lateral chest wall (seen on sonography) and the volume of pleural fluid punctured.

The study was approved by the hospital Ethics Committee. Eighty-seven consecutive critically ill patients underwent a pleural puncture when ultrasound analysis revealed a lamella of more than 2 cm [2]. A total of 138 pleural punctures was performed in 87 individuals. Ultrasound was performed using the ACUSON, sequoia 512, with the patient in the semirecumbent position. The deepest possible puncture side in this position was marked for pleural puncture. The PE was gradually drained, 200 ml at a time, until the fluid was completely evacuated. The width of the pre-puncture effusion lamella as measured with ultrasound was compared case by case with the actual punctured volume. Statistical analysis was performed using linear regression analysis and Spearman (rank) correlation coefficient.

Due to technical difficulties or missing data, 7 punctures had to be excluded. 131 punctures (67 on the left hemithorax and 64 on the right) remained for analysis. No complications were encountered as a consequence of the pleural puncture.

The sonographic measurements correlated very well with actual effusion volume on the left (r_s = 0.83) and the right side (r_s = 0.77). For both sides the level of statistical significance was taken as P < 0.001.

The thickness of the fluid lamella was taken as the independent variable, while the actual effusion volume was taken as the dependent variable. The linear sonographic method was represented by the equation y = 208.77×-317.12 (left), and y = 178.38×-159.7 (right). Y is the predicted effusion volume in milliliters and × is the sonographically measured thickness of the effusion lamella in centimeters. The mean predicted error was 199.7 ml for the left side and 285.3 ml for the right side.

There is a strong correlation between the sonographic measurements and the actual effusion volume which was punctured. Unlike the findings of other authors, we were not able to predict the punctured volume, based on the width of the lamella measured by sonography probably due to the wide spread of obtained data (scatter plot).