The role of ultrasound in determining the amount of pleural effusion

Abstract

Background: There is no standardized system to evaluate pleural effusion size on ultrasound (US). We aimed to explore the role of US in determining the amount of pleural effusion, with an attempt to provide evidence for clinical efficacy evaluation and treatment program selection.

Methods: A total of 98 patients undergoing thoracoscopy at our center were enrolled in this study. The patients take a sitting position, then the maximum depths of the pleural effusion by US at the subscapular line, posterior axillary line, midaxillary line, anterior axillary line, and midclavicular line, as well as the maximum thickness of the pleural effusion at the subscapular line, were measured before pleural effusion drainage. Then, the corresponding values in the lateral position were also measured. The relationships between the actual pleural effusion amounts and the measurements at these lines were analyzed using the multivariate linear regression model (MLRM).

Results: The regression equation of the group with a pleural effusion amount of 500-1,000 mL in the sitting position showed statistical significance (P=0.001). The P values of the maximum depths at the subscapular line (X₁) and midclavicular line (X₅) and the maximum thickness at the subscapular line (X₆) were below 0.05. Thus, a final model was established using X₁, X₅, and X₆ as the independent variables.

Conclusions: The combination of US examination and MLRM enables the quantitative determination of pleural effusion.

Keywords: Pleural effusion; logistic regression; ultrasound (US).

Figure 1

Measured pleural effusion depth at the midaxillary line (A) and subscapular line (B) in the sitting position. Massive effusion (E) causing atelectasis of the lung (L) by compression. The diaphragm (D) becomes clearly visible through the effusion.

Figure 2

The standardized residuals histogram of the 500–1,000 mL pleural effusion group (the residuals obey normal distribution, the abscissa is the regression standardized residual and the ordinate is the frequency, mean: 1.43 E. 15, standard deviation: 0.928, N=44, dependent variable: Y).

Figure 3

The normal P-P plot of regression standardized residuals (dependent variable: Y, independent variables for the cumulative probability, the abscissa is the observed cumulative feasibility and the ordinate is the expected cumulative feasibility).

Figure 4

ROC curves for pleural thickening, transparency, and echo of pleural effusion. For pleural thickening, the AUC was 0.762, 95% CI: 0.660–0.864, P=0.000, sensitivity: 69.1%, specificity: 83.3%. For transparency, the AUC was 0.806, 95% CI: 0.710–0.903, P=0.000, sensitivity: 77.9%, specificity: 83.3%. For echo, the AUC was 0.910, 95% CI: 0.838–0.981, P=0.000, sensitivity: 94.1%, specificity: 83.3%. ROC, receiver operating characteristic; AUC, area under the ROC curve.