The effect of recalibration on trending ability between two methods on determining cardiac output

Abstract

To the Editor: Fot et al. measured noninvasive continuous cardiac output/index (CO/CI) using pulse wave transit time (PWTT)-based esCCO (estimated continuous cardiac output) and compared it to CI measured by conventional pulse contour analysis (CIpca) in 10 stages during an 18-hour measurement period targeting patients who entered the cardiac ICU after off-pump coronary artery bypass surgery [1]. The differences between each CI in adjacent stages were analyzed in 4-quadrant plots, and a concordance rate of 70% was reported, which was clinically unacceptable. The authors suggested the following reasons for this were:1A reference study [2] used transpulmonary thermodilution (TPTD), but this study used measurement values obtained by pulse contour analysis.2The number of stages with a rapid change in CO increased.3PWTT is related to pulse pressure (PP), and the change in PP is less sensitive to changes in blood volume and is nonlinear [3]. Reason 1. is highly possible since Smetkin et al. [8] reported a concordance rate of 74% in polar plot analysis for evaluating trends in CIpca and TPTD. Reason 2. may not necessarily be a reason for the poor concordance of the two methods. A previous study by Tsutsui et al. [7] reported a concordance rate of 96% by evaluating after a change to head up, after a change to head down, after a volume challenge, during the Pringle maneuver, and after the release of the Pringle maneuver as stages during partial hepatectomy. It is unknown whether reason 3. is the reason for the difference from previous studies. However, the low concordance rate reported by Fot et al. may be due to reasons not included in the above, such as different conditions of analysis. In previous studies [4-6] with esCCO where a concordance rate exceeds 90%, calibration was performed only once before the whole study, but Fot et al. performed recalibration three times during the 10 stages of the study. By performing recalibration, CI may change discontinuously. For example, Study Limitations indicate that CIpca may drift after calibration by TPTD. There should also be a staircase-like change in esCCO before and after recalibration. The concordance rate will decrease unless the discontinuous changes in each CI match after recalibration. Therefore, changes in CI before and after recalibration in evaluating trending ability should not be included in the analysis. Although accuracy evaluated by Bland-Altman analysis improves by frequently performing recalibration, it should be recognized that trending ability does not necessarily improve. In conclusion, I believe recalibration, while improving the accuracy of cardiac output measurement by esCCO, may impact the correlation of the trending ability. [1] Fot EV, Smetkin AA, Volkov DA, Semenkova TN, Paromov KV, Kuzkov VV, Kirov MY. The validation of cardiac index and stroke-volume variation measured by the pulse-wave transit time-analysis versus conventional pulse-contour analysis after off-pump coronary artery bypass grafting: Observational study. J Cardiothorac Vasc Anesth. 2023; 37: 919-926.[2] Smetkin AA, Hussain A, E Fot EV, et al. Estimated continuous cardiac output based on pulse wave transit time in off-pump coronary artery bypass grafting: A comparison with transpulmonary thermodilution. J Clin Monit Comput 2017 Apr;31(2):361-370.[3] YL Manach Y, Hofer CK, Lehotet. JJ, et al. Can changes in arterial pressure be used to detect changes in cardiac output during volume expansion in the perioperative period? Anesthesiology 2012; 117: 1165-74.[4] Smetkin AA, Hussain A, Kuzkovet VV, et al. Validation of cardiac output monitoring based on uncalibrated pulse contour analysis vs transpulmonary thermodilution during off-pump coronary artery bypass grafting. Br J Anaesth. 2014; 112: 1024-31.[5] Tsutsui M, Araki Y, Masui K, et al. Pulse wave transit time measurements of cardiac output in patients undergoing partial hepatectomy: Comparison of the esCCO system with thermodilution. Anesth Analg. 2013; 117: 1307-12.[6] Terada T, Oiwa A, Maemura Y, et al. Comparison of the ability of two continuous cardiac output monitors to measure trends in cardiac output: estimated continuous cardiac output measured by modified pulse wave transit time and an arterial pulse contour-based cardiac output device. J Clin Monit Comput. 2016; 30: 621-7.[7] Terada T, Ochiai R. Comparison of the ability of two continuous cardiac output monitors to detect stroke volume index: Estimated continuous cardiac output estimated by modified pulse wave transit time and measured by an arterial pulse contour-based cardiac output device. Technol Health Care. 2021; 29: 499-504.[8] Magliocca A, Rezoagli E, Andersonet TA, et al. Cardiac output measurements based on the pulse wave transit time and thoracic impedance exhibit limited agreement with the thermodilution method during orthotopic liver transplantation. Anesth Analg. 2018;126: 85-92. The author, Ryoichi Ochiai: none