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

Abstract

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. Attempts to quantify pleural fluid using TOE are restricted to a case report in which volume was predicted by multiplying maximal cross-sectional area (CSA(max)) by axial length (AL). A computed tomography (CT) derived formula for quantifying pleural effusions is maximal effusion depth squared (d2) multiplied by maximal effusion length. Eight patients were studied before chest closure following coronary bypass surgery. Fifty millilitre saline aliquots were instilled into the pleural space until detected by TOE. Saline was then instilled up to the next 200 ml increment and further 200 ml aliquots added until it spilled from the pleural space. CSA(max), d and AL were measured for each stage and used to calculate pleural fluid volume. Median detection volume (range) was 125 ml (50-200) on the left and 225 ml (150-300) on the right (P = 0.016). Volume calculated by CSA(max) x AL correlated strongly with actual volume (r2 = 0.93 left and 0.92 right) as did volume calculated by d2 x AL (r2 = 0.86 left and 0.89 right). Mean difference between 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 volume calculated by d2 x AL. TOE detects small volumes of pleural fluid on both sides of the chest. CSA(max) x AL provides a reasonably accurate measure of pleural fluid volume.