Validation of equations for pleural effusion volume estimation by ultrasonography

To validate the accuracy of previously published equations that estimate pleural effusion volume using ultrasonography.

Only equations using simple measurements were tested. Three measurements were taken at the posterior axillary line for each case with effusion: lateral height of effusion (H), distance between collapsed lung and chest wall (C) and distance between lung and diaphragm (D). Cases whose effusion was aspirated to dryness were included and drained volume was recorded. Intra-class correlation coefficient (ICC) was used to determine the predictive accuracy of five equations against the actual volume of aspirated effusion.

46 cases with effusion were included. The most accurate equation in predicting effusion volume was (H + D) × 70 (ICC 0.83). The simplest and yet accurate equation was H × 100 (ICC 0.79).

Pleural effusion height measured by ultrasonography gives a reasonable estimate of effusion volume. Incorporating distance between lung base and diaphragm into estimation improves accuracy from 79% with the first method to 83% with the latter.