Comment on "Noninvasive cardiac output measurements are inaccurate in patients with severe aortic valve stenosis undergoing transcatheter aortic valve implantation"

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Korean J Anesthesiol. 2023;76(2):160-161
Publication date (electronic) : 2022 August 16
doi :
Department of Anesthesia and Intensive Care, IRCCS Humanitas Research Hospital, Milan, Italy
Corresponding author: Enrico Giustiniano, M.D. Department of Anesthesia and Intensive Care, IRCCS Humanitas Research Hospital, via Manzoni 56, 20089, Rozzano, Milan, Italy Tel: +39-0282247459 Fax: +39-0282244190 Email:
Received 2022 July 16; Accepted 2022 August 15.

We read with interest the paper by Yahagi et al. [1] regarding the reliability and cardiac output (CO) measurement agreement between the non-invasive ClearSight method connected to the EV1000 Clinical Platform (Edwards Lifesciences, USA) and the pulmonary artery catheter (PAC) thermodilution method connected to the Monitor KitTM (Edwards Life­sciences, USA) in patients who underwent transcatheter aortic valve implantation (TAVI). The authors concluded that the non-invasive method was “not as accurate as transpulmonary thermodilution for measuring CO. Therefore, ClearSight cannot be used in patients with severe [aortic stenosis] undergoing TAVI.” Although we congratulate the authors for their painstaking work and agree with their conclusions, some issues are worthy of discussion and clarification.

In our opinion, TAVI is not an appropriate setting to compare the ClearSight and PAC methods because they provide measurements at two different points of circulation, namely, downstream and upstream of the aortic valve, respectively. During aortic valve placement, surgical maneuvers alter the blood pressure waveform, and consequently, pulse contour analysis and CO computing. Furthermore, the PAC and ClearSight measure the right and left ventricle CO, respectively. The two CO measurements should be equivalent if the tricuspid and aortic valves are normal. However, in the case of tricuspid regurgitation (for the PAC) and aortic stenosis and/or regurgitation (for ClearSight), CO measurements can be profoundly affected. Among the limitations of the study, the authors did cite the issue of aortic regurgitation; however, they should have better clarified how aortic valve diseases would affect the measurements. Such differences should be expected even without a specific targeted study.

Moreover, blood pressure, which is the result of the interaction between the heart, blood volume, and circulatory bed, is expected to differ depending on whether it is measured invasively or non-invasively [2]. Conversely, Wang et al. [3] found both acceptable agreement and discrepancies between these two methods of hemodynamic monitoring during cardiac surgery. Using the same devices in a larger sample, the authors found that the mean ClearSight CO was 4.21 L/min and the mean PAC CO was 3.90 L/min, with a mean bias of 0.32 L/min, a 95% CI of 0.22–0.42 L/min, and a percentage error as low as 26.4%. We believe that Wang et al. [3] considered the limitations of comparing the two different CO measurement sites and the effect of valvular disease because they excluded patients with cardiac valvular disease of the tricuspid and aortic valves. In addition, the method used by Yahagi et al. [1] to average the ClearSight CO is problematic, since they used only two values to compute the average ClearSight CO value, whereas they used six values to compute the average PAC CO.

We also believe that their analysis of systemic vascular resistance (SVR) deserves some comment. Currently, the use of SVR (or SVRI if indexed) is a debatable issue. As reported by Magder, the principles behind SVRI computation are not applicable to human circulation: Poiseuille’s Law implies that the resistance within a pipe is determined by the ratio of the pressure gradient between the two ends over the inside flow. However, human circulation cannot be considered a pipe or electric circuit. In fact, this oversimplification does not consider the auto-regulatory mechanisms, one for each organ, which make blood flow vary according to the tissue demand, which we cannot currently “measure” at bedside [4,5]. Furthermore, these mechanisms are affected differently by anesthesia and various diseases. Thus, the standard SVRI computation method is limited and ineffective, if not misleading, for hemodynamic assessment. In addition, from a mere mathematical perspective, computing the SVRI value from the CO to explain the discrepancy between CO measurements is redundant and will not lead to any significant finding.

In conclusion, if properly employed, the non-invasive method of CO measurement is generally suitable and reliable for the intraoperative assessment and management of hemodynamics. However, the operator should be aware of the advantages and disadvantages of such devices. The surgical setting must also be considered as a critical factor that can limit the reliability of hemodynamic assessments. Finally, we emphasize that the cardiac index is preferable over the CO as it represents a more patient-related value of blood flow.




Conflicts of Interest

Enrico Giustiniano is an Edwards Lifescience European Proctor for Acumen monitoring system.

Author Contributions

Enrico Giustiniano (Writing – original draft; Writing – review & editing)

Fulvio Nisi (Writing – original draft; Writing – review & editing)

Federico Piccioni (Writing – original draft; Writing – review & editing)


1. Yahagi M, Omi K, Maeda T. Noninvasive cardiac output measurements are inaccurate in patients with severe aortic valve stenosis undergoing transcatheter aortic valve implantation. Korean J Anesthesiol 2022;75:151–9.
2. Giustiniano E, Chiurazzi C, Nisi F, Cecconi M. Continuous non-invasive blood pressure vs invasive blood pressure during anesthesia. Have they the same safe reference value? J Cardiol Cardiovasc Res 2021;2:15–20.
3. Wang Y, Huang W, Han J, Tian Y, Wang C, Li L. A comparison of ClearSight noninvasive cardiac output and pulmonary artery bolus thermodilution cardiac output in cardiac surgery patients. Perioper Med (Lond) 2022;11:24.
4. Magder SA. The highs and lows of blood pressure: toward meaningful clinical targets in patients with shock. Crit Care Med 2014;42:1241–51.
5. Meng L. Heterogeneous impact of hypotension on organ perfusion and outcomes: a narrative review. Br J Anaesth 2021;127:845–61.

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