• Chahyun Oh, Hyung-Chul Lee, Soomin Lee, Man-Shik Shim, Soo Bin Yoon, Jinsik Jung, Seok-Hwa Yoon, Yoon-Hee Kim, Youngkwon Ko, Boohwi Hong, and Yunseo Ku.
• Department of Anesthesiology and Pain Medicine, Chungnam National University Hospital, Daejeon, Korea.
• J Anesth. 2024 Feb 1; 38 (1): 191-9.

PurposeSeveral technical aspects of the Fick method limit its use intraoperatively. A data-driven modification of the Fick method may enable its use in intraoperative settings.MethodsThis two-center retrospective observational study included 57 (28 and 29 in each center) patients who underwent off-pump coronary artery bypass graft (OPCAB) surgery. Intraoperative recordings of physiological data were obtained and divided into training and test datasets. The Fick equation was used to calculate cardiac output (CO-Fick) using ventilator-determined variables, intraoperative hemoglobin level, and SvO2, with continuous thermodilution cardiac output (CCO) used as a reference. A modification CO-Fick was derived and validated: CO-Fick-AD, which adjusts the denominator of the original equation.ResultsIncreased deviation between CO-Fick and CCO was observed when oxygen extraction was low. The root mean square error of CO-Fick was decreased from 6.07 L/min to 0.70 L/min after the modification. CO-Fick-AD showed a mean bias of 0.17 (95% CI 0.00-0.34) L/min, with a 36.4% (95% CI 30.6-44.4%) error. The concordance rates of CO-Fick-AD ranged from 73.3 to 87.1% depending on the time interval and exclusion zone.ConclusionsThe original Fick method is not reliable when oxygen extraction is low, but a modification using data-driven approach could enable continuous estimation of cardiac output during the dynamic intraoperative period with minimal bias. However, further improvements in precision and trending ability are needed.© 2023. The Author(s) under exclusive licence to Japanese Society of Anesthesiologists.

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