Basic critical care echocardiography training of intensivists allows reproducible and reliable measurements of cardiac output

Abstract

Background Although pulmonary artery catheters (PACs) have been the reference standard for calculating cardiac output, echocardiographic estimation of cardiac output (CO) by cardiologists has shown high accuracy compared to PAC measurements. A few studies have assessed the accuracy of echocardiographic estimation of CO in critically ill patients by intensivists with basic training. The aim of this study was to evaluate the accuracy of CO measurements by intensivists with basic training using pulsed-wave Doppler ultrasound vs. PACs in critically ill patients. Methods Critically ill patients who required hemodynamic monitoring with a PAC were eligible for the study. Three different intensivists with basic critical care echocardiography training obtained three measurements of CO on each patient. The maximum of three separate left-ventricular outflow tract diameter measurements and the mean of three LVOT velocity time integral measurements were used. The inter-observer reliability and correlation of CO measured by PACs vs. critical care echocardiography were assessed. Results A total of 20 patients were included. Data were analyzed comparing the measurements of CO by PAC vs. echocardiography. The inter-observer reliability for measuring CO by echocardiography was good based on a coefficient of intraclass correlation of 0.6 (95% CI 0.48–0.86, p < 0.001). Bias and limits of agreement between the two techniques were acceptable (0.64 ± 1.18 L/min, 95% limits of agreement of − 1.73 to 3.01 L/min). In patients with CO < 6.5 L/min, the agreement between CO measured by PAC vs. echocardiography improved (0.13 ± 0.89 L/min; 95% limits of agreement of − 1.64 to 2.22 L/min). The mean percentage of error between the two methods was 17%. Conclusions Critical care echocardiography performed at the bedside by intensivists with basic critical care echocardiography training is an accurate and reproducible technique to measure cardiac output in critically ill patients. Electronic supplementary material The online version of this article (10.1186/s13089-019-0120-0) contains supplementary material, which is available to authorized users.

Feasibility of cardiac output measurements in critically ill patients by medical students

“…Whether images obtained are of sufficient quality should preferably be judged by independent experts, as two out of four studies did [22,34]. In one study independent investigators assessed the quality, however, it is not clear if these were experts or not [35]. The percentage of adequate/good-quality images in our study was comparable with Dinh et al In the study of Betcher et al and Villavicencio et al, image quality was generally (judged) overall lower.…”

“…If reported, results may vary based on differences in ultrasonography training and experience, which impedes a comparison of image acquisition and quality. We found four studies, on measuring CO in critically ill patients by non-experts to compare with our study (see Additional file 1) [22,23,34,35]. In two out of the four studies the operators had previous experience with ultrasonography, but training varied [23,34].…”

Rationale for using the velocity–time integral and the minute distance for assessing the stroke volume and cardiac output in point-of-care settings

“…Regarding reliability, if expected physiologic responses range between increments of at least 15% in VTI after an intervention, intra-and interobserver variability for the measurement of VTI must be lower than these values, otherwise, the margin of error may exceed the patient's physiologic response. Regarding this point, the reported intra-and interobserver variabilities are low among studies (ranging between 3 and 8%) [16,24,29,38]. In a recent study, the lowest smallest change for the LVOT VTI (i.e., the smallest change that can be considered as significant and not related to the imprecision of the method or the variability of the parameter) was found to be < 5% for intra-examinations (i.e., without removing the probe from the chest wall), while it averages 11% for inter-examinations (i.e., removing the probe from the chest wall) [37].…”

“…The consensus on circulatory shock and hemodynamic monitoring by the Task Force of the European Society of Intensive Care Medicine provides a similar recommendation as well [9]. Besides its recommendation, it is important to note that there is conflicting evidence regarding the interchangeability between echocardiography and the pulmonary artery catheter or CO monitors for estimating the SV or CO, with some studies not showing a good correlation between them [10][11][12][13] and many studies showing the opposite [14][15][16][17][18].…”

Reduced pulmonary vascular reserve during stress echocardiography in confirmed pulmonary hypertension and patients at risk of overt pulmonary hypertension

“…All echocardiographers had passed quality control of reading examinations as required by Stress Echo 2020 study with interobserver reproducibility ≥ 90% [ 20 ]. CO was derived from the Doppler-estimated stroke volume (SV) using the velocity time integral of flow through the left ventricular outflow tract [ 21 – 25 ]. Pulmonary vascular resistance (PVR) was calculated using Abbas formula: PVR (Wood Units) = TRV (m/s) /VTI RVOT (cm) * 10 + 0.16 and assessed separately in two time points at baseline and peak exercise [ 26 , 27 ].…”