Cardiac output in critically ill patients can be estimated easily and accurately using the minute distance obtained by pulsed wave doppler
Authors: Villavicencio Christian , Daniel Xavier , Cartanyá Marc , Leache Julen , Ferré Cristina , Roure Marina , Bodí María , Vives Marc , Rodriguez Alejandro 
Published: September 2023

ABSTRACT

Background
Cardiac output (CO) assessment is essential for management of patients with circulatory failure. Among the different techniques used for their assessment, pulsed-wave Doppler cardiac output (PWD-CO) has proven to be an accurate and useful tool. Despite this, assessment of PWD-CO could have some technical difficulties, especially in the measurement of left ventricular outflow tract diameter (LVOTd). The use of a parameter such as minute distance (MD) which avoids LVOTd in the PWD-CO formula could be a simple and useful way to assess the cardiac output in critically ill patients. Therefore, the aim of this study was to evaluate the correlation and agreement between PWD-CO and MD.

Methods
A prospective and observational study was conducted over 2 years in a 30-bed intensive care unit (ICU). Adult patients who required CO monitoring were included. Clinical echocardiographic data were collected within the first 24 h and at least once more during the first week of ICU stay. PWD-CO was calculated using the average value of three LVOTd and left ventricular outflow tract velocity-time integral (LVOT-VTI) measurements, and heart rate (HR). MD was obtained from the product of LVOT-VTI × HR. PWD-CO was correlated with MD using linear regression. CO was quantified from the MD (MD-CO) using the equation defined by linear regression. Bland–Altman analysis was also used to evaluate the level of agreement between MD-CO and PWD-CO. The percentage error (PE) was calculated.

Results
A total of 98 patients and 167 CO measurements were analyzed. Sixty-seven (68%) were male, the median age was 66 years (IQR 53-75) and the median APACHE II score was 22 (IQR 16-26). The most common cause of admission was shock in 81 (82.7%) patients. 69 (70.4%) patients were mechanically ventilated and 68 (70%) required vasoactive drugs. The median CO was 5.5 L/min (IQR 4.8 – 6.6) and the median MD was 1850 cm/min (IQR 1520-2160). There was a significant correlation between PWD-CO and MD-CO in the general population (R2 = 0.7; p < 0,05). This correlation improved when left ventricular ejection fraction (LVEF) was less than 60% (R2 = 0.85, p < 0.05). Bland-Altman analysis showed good agreement between PWD-CO and MD-CO in the general population, the median bias was 0.02 L/min, the limits of agreement (LOAs) were -1.92 to +1.92 L/min. The agreement was better in patients with LVEF less than 60% with a median bias of 0.005 L/min, LOAs -1.56 to 1.55 L/min. The PE was 17% in both cases.

Conclusions
Measurement of MD in critically ill patients provides a simple and accurate estimate of cardiac output, especially in patients with reduced or preserved LVEF. This would allow earlier cardiovascular assessment in patients with circulatory failure, which is of particular interest in difficult clinical or technical conditions.
Conflict of interest declaration: The authors declare that they have NO affiliations with or involvement in any organization or entity with any financial interest in the subject matter or materials discussed in this manuscript.