Technical note: validation of cardiac output monitoring tools

To date, tools for continuous cardiac output (CO) monitoring have been validated as if they were tools for snapshot measurements. Most authors compared variations in cardiac output between two time-points and used Bland & Altman representations to describe the agreement between these variations. The impact of repetitive measurements over time is not taken into consideration. This article proposes a conceptual framework for the validation of CO monitoring devices. The proposal consists of eight quality criteria: 1) accuracy (small bias); 2) linearity by comparing the regression line of the study and reference technology with the identity line; 3) precision (small random error of measurements); 4) least significant change; 5) stability (absence of time drift for the first four criteria); 6) measurement range where the first five criteria are fulfilled; 7) short response time; and 8) accurate amplitude response. Because tolerance is obviously admitted for each of these eight criteria, we propose to add as final criterion, the ability to detect significant CO directional changes. Other important issues in designing studies to validate CO monitoring tools are reviewed: choice of patient population to be studied, choice of the reference method, data acquisition method, data acceptability checking, data segmentation and final evaluation of reliability. Application of this framework will underline the importance of precision and time response for clinical acceptability of monitoring tools.