Page 14 - Delaware Medical Journal - September 2016

The Impact of Direct Cardiac Output Determination on Using a Widely Available Direct Continuous Oxygen Consumption Measuring Device on the Hemodynamic Assessment of Aortic Valve
Zaher Fanari, MD; Matthew Grove, DO; Anitha Rajamanickam, MD; Sumaya Hammami, MD, MPH; Cassie Walls, RT; Paul Kolm, PhD; Mitchell Saltzberg, MD; William Weintraub, MD; Andrew J. Doorey, MD
Background: Accurate assessment of cardiac output (CO) is essential for the hemodynamic assessment of aortic valve
area (AVA). Estimation of oxygen consumption (VO2) and Thermodilution (TD) is employed in many cardiac catheterization laboratories (CCL) given the historically cumbersome nature of direct continuous VO2 measurement, the “gold standard” for this technique. A portable facemask device simplifies the direct continuous measurement of VO2, allowing for relatively rapid and continuous assessment of CO and AVA.
Methods and Materials: Seventeen consecutive patients undergoing right heart catheterization had simultaneous determination of CO by both direct continuous and assumed VO2 and TD. Assessments were only made when a plateau of VO2 had occurred. All measurements of direct continuous and assumed VO2, as well as, TD CO were obtained in triplicate.
Results: Direct continuous VO2 CO and assumed VO2 CO correlated poorly (R= 0.57; ICC =0.59). Direct continuous VO2 CO and TD CO also correlated poorly (R= 0.51; ICC=0.60). Similarly AVA derived from direct continuous VO2 correlated poorly with those of assumed VO2 (R= 0.68; ICC=0.55) and TD (R=0.66, ICC=0.60). Repeated direct continuous VO2 CO and AVA measurements were extremely correlated and reproducible [(R=0.93; ICC=0.96) and (R=0.99; ICC>0.99) respectively], suggesting that this was the most reliable measurement of CO.
Conclusions: CO calculated from direct continuous VO2 measurement varies substantially from both assumed VO2 and TD based CO, which are widely used in most CCL. These differences may significantly impact the CO and AVA measurements. Furthermore, continuous, rather than average, measurement of VO2 appears to give highly reproducible results.
Key Words: Direct Continuous Oxygen Consumption, Assumed Oxygen Consumption, Thermodilution, Cardiac Output, Aortic Valve Area
Introduction
Cardiac output (CO) is an important parameter of cardiac performance,
an accurate assessment of which
is an important function of cardiac catheterization laboratories (CCL).1 This is especially true in valvular disorders, e.g., in patients with equivocal echo calculated for suspected aortic stenosis (AS).2 A precise measurement of CO and consequently the degree of AS severity is crucial to ensure that only
appropriate patients are referred for valve replacement and to prevent both premature or inappropriately delayed aortic valve replacement.3
A widely used CO method is the Fick equation, in which the total uptake or release of a substance, such as oxygen, by through the organ and the arteriovenous concentration difference of the substance.4 When oxygen consumption is directly measured, this is called direct oxygen consumption (Direct, VO2) and is widely
considered the gold standard for CO measurement. Alternatively CO can be calculated using estimated VO2.
Historically VO2 was directly measured using a Douglas bag over many minutes,
a cumbersome affair. Therefore an estimation of VO2 is used instead in many CCL, with VO2 values typically estimated from tables or published predictive equations.5-8 Reliability and use of predictive equations for CO measurement have been questioned in the CCL setting because of large discrepancies between
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Del Med J | September 2016 | Vol. 88 | No. 9
Abstract