Volumetric preload measurement by thermodilution: a comparison with transoesophageal echocardiography

Background. End-diastolic volume indices determined by transpulmonary thermodilution and pulmonary artery thermodilution may give a better estimate of left ventricular preload than pulmonary capillary wedge pressure monitoring. The aim of this study was to compare volume preload monitoring using the two different thermodilution techniques with left ventricular preload assessment by transoesophageal echocardiography (TOE). Methods. Twenty patients undergoing elective cardiac surgery with preserved left-right ventricular function were studied after induction of anaesthesia. Conventional haemodynamic variables, global end-diastolic volume index using the pulse contour cardiac output (PiCCO) system (GEDVI(PiCCO)), continuous end-diastolic volume index (CEDVIPAC) measured by a modified pulmonary artery catheter (PAC), left ventricular end-diastolic area index (LVEDAI) using TOE and stroke volume indices (SVI) were recorded before and 20 and 40 min after fluid replacement therapy. Analysis of variance (Bonferroni-Dunn), Bland-Altman analysis and linear regression were performed. Results. GEDVI(PiCCO), CEDVIPAC, LVEDAI and SVIPiCCO/PAC increased significantly after fluid load (P< 0.05). An increase > 10% for GEDVI(PiCCO) and LVEDAI was observed in 85% and 90% of the patients compared with 45% for CEDVIPAC. Mean bias (2 sd) between percentage changes (Δ) in GEDVI(PiCCO) and Δ LVEDAI was -3.2 (17.6)% and between Δ CEDVIPAC and Δ LVEDAI -8.7 (30.0)%. The correlation coefficient (r(2)) for Δ GEDVI(PiCCO) vs Δ LVEDAI was 0.658 and for Δ CEDVIPAC vs Δ LVEDAI 0.161. The relationship between Δ GEDVI(PiCCO) and Δ SVIPiCCO was stronger (r(2)=0.576) than that between Δ CEDVIPAC and Δ SVIPAC (r(2)=0.267). Conclusion. GEDVI assessed by the PiCCO system gives a better reflection of echocardiographic changes in left ventricular preload, in response to fluid replacement therapy, than CEDVI measured by a modified PAC.