Introduction: From 2010 onwards, guidelines, including those of the British Thoracic Society (BTS), recommend the use of ultrasound in all pleural fluid evaluation procedures. There are various established formulas to estimate the pleural fluid volume using ultrasonography. The two formulas by Goecke and Schwerk, Einberger’s formula, Balik’s formula, and Usta’s formula are some of the most commonly used ones. But considering only a single or a couple of measurements to estimate the total volume of pleural effusion, especially moderate to large effusions, will definitely have its own disadvantages. The objective of the PLEURA 1 study was to develop a new multi- site ultrasound-based model for a more accurate estimation of the pleural fluid volume and to compare it with the existing formulae.
Materials and Methods: PLEURA 1, a prospective observational study, was conducted in a tertiary care center in South India. A novel multisite parameter (Mean9) was defined using nine different ultrasonographic dimensions. Pearson correlation coefficients (r) were calculated to assess the strength of association between predicted and actual pleural fluid volume. Model performance was assessed using the coefficient of determination (R²), mean absolute error (MAE), and root mean square error (RMSE) and compared with that of the existing erect position formulas.
Results: The study cohort consisted of twenty-four patients with pleural effusion. Mean9 demonstrated a strong linear relationship with actual pleural fluid volume (Pearson r = 0.853, 95% CI 0.68–0.94; p < 0.0001). ‘Paul’s formula’, ‘V = 41.4 + 270.8 × Mean9’ was derived using linear regression. Paul’s formula maintained the highest predictive performance among all evaluated models (LOOCV r = 0.820, LOOCV R² = 0.672, MAE = 422 mL, RMSE = 504 mL), and demonstrated better correlation to actual pleural fluid volume than the established erect-position formulas.
Conclusion: PLEURA 1 study and Paul’s formula suggest that incorporating multiple dimensions of the pleural effusion into a predictive model may improve the estimation of pleural fluid volume. PLEURA 2 validation study will be the second phase of the study, where Paul’s formula will be applied along with other established formulae in an entirely new and larger cohort.