Transoesophageal echocardiography for the detection and quantification of pleural fluid in cardiac surgical patients

Background: Transoesophageal echocardiography (TOE) can image pleural fluid.Left pleural collections may be easier to detect than right,as the thoracic aorta serves as an acoustic window. Attemptsto quantify pleural fluid using TOE are restricted to a casereport in which volume was predicted by multiplying maximalcross-sectional area (CSA_max) by axial length (AL). A computedtomography (CT) derived formula for quantifying pleural effusionsis maximal effusion depth squared (d²) multiplied by maximaleffusion length. Methods: Eight patients were studied before chest closure following coronarybypass surgery. Fifty millilitre saline aliquots were instilledinto the pleural space until detected by TOE. Saline was theninstilled up to the next 200 ml increment and further 200 mlaliquots added until it spilled from the pleural space. CSA_max,d and AL were measured for each stage and used to calculatepleural fluid volume. Results: Median detection volume (range) was 125 ml (50–200) onthe left and 225 ml (150–300) on the right (P = 0.016).Volume calculated by CSA_max x AL correlated strongly with actualvolume (r² = 0.93 left and 0.92 right) as did volume calculatedby d² x AL (r² = 0.86 left and 0.89 right). Mean differencebetween volume calculated by CSA_max x AL and actual volume was– 51 ml on the left and 45 ml on the right vs –253 ml on the left and – 212 ml on the right for volumecalculated by d² x AL. Conclusions: TOE detects small volumes of pleural fluid on both sides ofthe chest. CSA_max x AL provides a reasonably accurate measureof pleural fluid volume.