Academic Resource

Case Report

Can Estimated Continuous Cardiac Output Be
Used in the Same Manner as Arterial PressureBased Cardiac Output?
Estimated continuous cardiac output (esCCO) is a new parameterfor estimating cardiac output (CO) and stroke volume (SV) andcontinuously displaying biological information using pulse waves
obtained with a pulse oximeter and electrocardiogram and bloodpressure*. *Either invasive or non-invasive measurement can be used for bloodpressure.

Associate Professor,
Department of Anesthesiology,
Toho University Omori Medical Center,Tokyo, Japan

Takashi Terada, MD, PhDI herein report on evaluation of the precision and trackability ofesCCO and the feasibility of fluid management using esCCO.

1. Introduction
Estimated continuous cardiac output (esCCO) is a technology for calculating cardiac output (CO) non-invasively andcontinuously using pulse wave transmit time (PWTT). PWTT is the transmit time of the pulse pressure waveformgenerated when blood from the left ventricle is released. Defining the start point as the electrocardiogram (ECG) R-wave
and the end point as the rise point where the differentiated pulse oximeter wave reaches 30% of its peak amplitude,
Nihon Kohden independently defined PWTT as the time from the start point to the end point. PWTT is comprised ofthe pre-ejection period (PEP) up to release of blood to the aortae, the time from the aortae to the radial artery (PWTT1),
and the time from the radial artery to the fingertip (PWTT2). PEP is affected by the contractile force of the heart, andPWTT2 is affected by peripheral vascular resistance. For esCCO, calculation of CO is begun by performing calibration
using patient characteristics. During calibration, pulse pressure is calculated from blood pressure, and CO is calculatedusing the formula esCCO = (K × PP) × HR. After calibration, CO is calculated non-invasively and continuously bymeans of continuous measurement of PWTT based on the formula esCCO = K × (α × PWTT + β) × HR (α: constant,β and K: constants determined by patient).1 According to the latest Enhanced Recovery After Surgery (ERAS) Society
Recommendations (2018),2 high-risk patients require proper adjustment of individual Frank-Starling curves using aminimally invasive cardiac output measurement device,3,4 improvement of intravascular volume and circulating blood
volume while evaluating the degree of dehydration is recommended for fluid therapy.5 Arterial pressure-based cardiac
output (APCO) is often used, but esCCO can be used without the risk of securing the radial artery and at a lower cost ascompared with APCO. The advantages of being able to use esCCO in the same manner as APCO are substantial.

2. Comparison of stroke volume index calculated using esCCO and stroke volumeindex calculated using APCO with the thermodilution method as the standard
We previously compared the precision of esCCO and the precision of APCO in kidney transplant patients with a historyof cardiovascular events, using CO measured by the thermodilution method with a pulmonary artery catheter as thestandard,6 and reported that the precision of CO calculated with esCCO was comparable to that of CO calculated withAPCO. These data were reanalyzed, and the precision of stroke volume index (SVI) calculated using esCCO (esSVI)
and SVI calculated using APCO (APSVI) was compared with that of SVI calculated using the thermodilution method(ISVI).7 Calibration was carried out using patient information and radial pulse pressure. The correlation coefficient ofesSVI and ISVI was 0.68, the bias was -3.0 cc/m2, and the precision was 8.8 cc/m2 (percentage error: 33.5%) (Fig. 1). The
correlation coefficient of APSVI and ISVI was 0.51, the bias was 0.9 cc/m2, and the precision was 11.2 cc/m2 (percentageerror: 42.6%) (Fig. 2). Like CO, the precision of esSVI was comparable to that of APSVI.

Figure 1 Bland-Altman analysis of esSVI and ISVI

Figure 2 Bland-Altman analysis of APSVI and ISVI

esCCO Case Report

3. Evaluation of trackability of esCCO using APCO as the standard
Next, we investigated the trackability of esCCO in non-cardiac surgery
without a change of position, using APCO as the standard.8 Improving
intravascular volume and circulating blood volume while evaluating thedegree of dehydration is recommended when performing fluid therapy
in high-risk patients. APCO is often used for this purpose, and fluid
responsiveness is used to evaluate it. If it can be demonstrated that esCCO
has trackability comparable to that of APCO, it could serve as a usefulparameter in clinical practice. APCO is considered to be more precise9,10than pulmonary artery catheter as long as there are no major changes in
hemodynamics and the fluid volume is not excessive. In our research, we
compared systemic vascular resistance index (SVRI),10 which is said tohave good APCO precision, using only data within the range of 1200-2500
dyn∙sec∙m2/cm-5, and assumed a central venous pressure of 11 mmHg whenmeasuring SVRI. We found a mean angular bias of 3.5°, a radial limit ofagreement of 28.3°, and trackability that trended well (Fig. 3).

Figure 3 Polar plot of esCCO and APCO

Discussion
We were able to confirm that SVI calculated using esCCO was not inferior to SVI calculated using APCO as comparedwith the thermodilution method. SVI is often employed as an index of volume load, and it is used as the standard for
fluid responsiveness. As such, it is used as a parameter for circulation management. Moreover, the trackability of esCCO
trended well with APCO as a control. There has been a report of a comparison of the thermodilution method and esCCO
in patients requiring a pulmonary artery catheter, and a report of a study that found no correlation or trackability.11,12,13
However, these reports involved studies in ICU patients and severe cases,12,13 i.e., patients with markedly unstable
hemodynamics following cardiac surgery,13 for instance. Although it has been reported that PWTT may accurately
measure SV despite changes in vascular resistance since it includes factors that reflect cardiac function and peripheral
vascular resistance, such as PEP and PWTT2,14 the precision of esCCO may decrease in situations where hemodynamics
are markedly unstable. The present results showed that SVI calculated using esCCO was equally precise as SVI calculatedusing APCO, and it was also found to trend well with APCO in terms of trackability. This suggests that it may be possible
to use esCCO in clinical practice. Due to its non-invasive nature, it could be used in various settings, such as fluid
management in the outpatient setting, in the examination room, and before and after surgery.

Summary
Having more clinical indicators such as cardiac output (stroke volume) in addition to blood pressure and pulse forpreoperative and postoperative management is effective for circulation management including safe fluid management ofpatients. Moreover, the ability to perform non-invasive measurement lends itself to a wide range of applications. However,the characteristics of the parameter need to be fully understood in order to maximize the effectiveness of the parameter.

References
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