Three-dimensional transoesophageal echocardiography for cardiac output in critically ill patients: A pilot study of ultrasound versus the thermodilution method.

Background: Three-dimensional transoesophageal echocardiography (3D-TOE) is a new noninvasive tool for quantitative assessment of left ventricular (LV) volumes and ejection fraction.

Aim: The objective of this pilot study was to evaluate the feasibility and accuracy of 3D-TOE for the estimation of cardiac output (CO), using transpulmonary thermodilution with the Pulse index Contour Continuous Cardiac Output (PiCCO) system as the reference method, in intensive care unit (ICU) patients.

Methods: Fifteen ICU patients on mechanical ventilation prospectively underwent PiCCO catheter implantation and 3D-TOE. 3D-TOE LV end-diastolic and end-systolic volumes were determined using semi-automated software. CO was calculated as the product of LV stroke volume (end-diastolic volume-end-systolic volume) multiplied by heart rate. CO was also determined invasively by transpulmonary thermodilution as the reference method.

Results: Among 30 haemodynamic evaluations, 29 (97%) LV 3D-TOE datasets were suitable for CO calculation. The mean 3D-TOE image acquisition and post-processing times were 46 and 155seconds, respectively. There was a correlation (r=0.78; P<0.0001) between PiCCO and 3D-TOE CO. Compared with PiCCO, the 3D-TOE CO mean bias was 0.38L/min, with limits of agreement of -1.97 to 2.74L/min.

Conclusions: Noninvasive estimation of CO by 3D-TOE is feasible in ICU patients. This new semi-automated modality is an additional promising tool for noninvasive haemodynamic assessment of ICU patients. However, the wide limits of agreement with thermodilution observed in this pilot study require further investigation in larger cohorts of patients.