Comparison of noninvasive electrical cardiometry and transpulmonary thermodilution for cardiac output measurement in critically ill patients: a prospective observational study

Background: Cardiac output (CO) monitoring is essential for diagnosing and managing critically ill patients. Recently, a non-invasive haemodynamic monitoring technique, electrical cardiometry (EC), has gathered increasing interest among ICU physicians. This study aimed to explore the accuracy of CO estimated by non-invasive EC (COEC) compared to CO determined by transpulmonary thermodilution (COTPTD) and to evaluate the ability of COEC to track COTPTD changes (Delta COTPTD). Methods: This prospective, observational, single-center study was conducted from April 2021 to April 2023, involving patients who required haemodynamic monitoring using a transpulmonary thermodilution device (PiCCO). COTPTD and COEC were recorded simultaneously, with the investigators obtaining the COEC measurements were blinded to the COTPTD results and vice versa. Agreement between the methods was evaluated using Bland-Altman analysis and percentage error (PE). The ability of COEC to track changes in COTPTD was examined using four-quadrant and polar plots. Results: Seventy-two patients with PiCCO haemodynamic monitoring were included, yielding 285 paired CO measurements. The bias between COEC and COTPTD was 0.47 L/min, with a limit of agreement (LoA) ranging from -2.91 to 3.85 L/min and a PE of 54.0%. Among 212 pairs of Delta CO data, excluding a central zone of 15% in the four-quadrant plot, the concordance rate between Delta COEC % and Delta COTPTD % was 70%. In the polar plot, excluding a central zone with a radius of 0.625 L/min (10% of the mean COTPTD), the mean polar angle for Delta COEC was 2.2 degrees, with a radial LoA of 56.0 degrees. Exploratory subgroup analysis indicated a PE of 47.0% between COEC and COTPTD and a concordance rate of 72% between Delta COEC% and Delta COTPTD% in patients with normal CO (CO >= 4 L/min). In patients with elevated thoracic fluid content (TFC > 35 k Omega), the PE between COEC and COTPTD was 45.0%, with a concordance rate of 64% between Delta COEC% and Delta COTPTD%. Additionally, in patients receiving low-dose norepinephrine equivalents (NEE <= 0.25 mu g/kg/min), COEC and COTPTD exhibited a PE of 45.0%, while Delta COEC% and Delta COTPTD% achieved a concordance rate of 75% and a radial LoA of 44.2 degrees. Conclusion: In critically ill patients, non-invasive EC indicated limited accuracy in measuring CO, along with a restricted ability to reliably track CO changes. These findings suggested that EC may not be interchangeable with TPTD in the general ICU population.