What is the lowest change in cardiac output that transthoracic echocardiography can detect?

Abstract

Background In critically ill patients, changes in the velocity-time integral (VTI) of the left ventricular outflow tract, measured by transthoracic echocardiography (TTE), are often used to non-invasively assess the response to fluid administration or for performing tests assessing fluid responsiveness. However, the precision of TTE measurements has not yet been investigated in such patients. First, we aimed at assessing how many measurements should be averaged within one TTE examination to reach a sufficient precision for various variables. Second, we aimed at identifying the least significant change (LSC) of these variables between successive TTE examinations. Methods We prospectively included 100 haemodynamically stable patients in whom TTE examination was planned. Three TTE examinations were performed, the first and the third by one operator and the second by another one. We calculated the precision and LSC (1) within one examination depending on the number of averaged measurements and (2) between measurements performed in two successive examinations. Results In patients in sinus rhythm, averaging three measurements within an examination was enough for obtaining an acceptable precision (interquartile range highest value < 10%) for VTI. In patients with atrial fibrillation, averaging five measurements was necessary. The precision of some other common TTE variables depending on the number of measurements is provided. Between two successive examinations performed by the same operator, the LSC was 11 [5–18]% for VTI. If two operators performed the examinations, the LSC for VTI significantly increased to 14 [8–26]%. The LSC between two examinations for other TTE variables is also provided. Conclusions Averaging three measurements within one TTE examination is enough for obtaining precise measurements for VTI in patients in sinus rhythm but not in patients with atrial fibrillation. Between two TTE examinations performed by the same operator, the LSC of VTI is compatible with the assessment of the effects of a 500-mL fluid infusion but is not precise enough for assessing the effects of some tests predicting preload responsiveness. Electronic supplementary material The online version of this article (10.1186/s13054-019-2413-x) contains supplementary material, which is available to authorized users.

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 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].…”

“…In these cases, it is recommended to average at least five VTIs in order to obtain a more accurate VTI value (Fig. 8) [23,37].…”

Prediction of Fluid Responsiveness by Stroke Volume Variation in Children Undergoing Fontan Operation

“…SVV in patients with mechanical ventilation is less than 10-15%. According to cardiopulmonary interaction under mechanical ventilation and Frank-Starling principle, a change in stroke volume caused by mechanical ventilation is more significant when the blood volume is insufficient, showing a negative correlation between SVV and the blood volume [ 16 , 17 ]. Theoretically, SVV can therefore be used to estimate the intravascular volume state and predict the responsiveness of the circulatory system to the infusion treatment.…”

Prediction of Volume Responsiveness by Stroke Volume Variation vs. Central Venous Pressure in Children Undergoing Fontan Operation

“…showing a negative correlation between SVV and the blood volume. (16,17) Theoretically, SVV can therefore be used to estimate the intravascular volume state and predict the responsiveness of the circulatory system to the infusion treatment.…”