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Accurate assessment of Cardiac Output (CO) is a critical measurement in the cardiac catheterization laboratory (CCL), especially in calculation of aortic valve area (AVA). Due to known inaccuracy of Fick assumptions, many measure Thermodilution (TD) CO as well. Most physicians assume that this more accurate measurement can be chosen to determine AVA. However, we have discovered that our popular computer system [Philips Xper Connect (XIM)] will use predetermined rules to assign one of the CO methods for the reported AVA.
We randomly selected one hundred consecutive patients who underwent right and left heart catheterization from 2009-2012 for assessment of aortic valve areas and had both Fick CO calculated using femoral and pulmonary arterial saturations and thermodilution CO performed for calculation of AVA. We then examined our XIMS system records for each of these procedures and documented the timing when each CO method was performed and reviewed which CO and AVA calculation appeared on the final catheterization report.
We found that whichever CO calculation was done first by the CCL computer system became the determinative output, appearing on the final report and being used to calculate the official AVA. In 32 patients the CO and AVA were calculated and displayed using the Fick calculation method, which had been performed first, and in 68.
patients TD was performed first and the AVA and CO were calculated and displayed using this CO. Although the second CO type could be selected on the computer during the case, and the computer screen would temporarily display the related AVA, this would never appear in the final report and may never be seen by the physician. Thus the CO used officially depended solely of the timing of the oxygen saturation samples. An intense effort of 11 non-intuitive computer clicks and multiple screen changes is required to make the second output the determinative value. The recommendation for surgery (AVA <1.0 cm2) was different between the CO methods in 12 cases (12% of patients).
Our widely used computer system has an arbitrary method of selecting the determinative CO to calculate the final AVA. For the more accurate TD CO to 'trump' the Fick CO an elaborate series of computer commands needs to be performed. None of the physicians or technicians was aware of this computer selection process, which affects critical treatment decisions.