Cardiac output determination using a widely available direct continuous oxygen consumption measuring device: a practical way to get back to the gold standard.

BACKGROUND: Accurate assessment of cardiac output (CO) is essential for the hemodynamic assessment of valvular heart disease. Estimation of oxygen consumption (VO2) and thermodilution (TD) are 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. METHODS AND MATERIALS: Thirty 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). Repeated direct continuous VO2 CO measurements were extremely correlated and reproducible [(R=0.93; ICC=0.96) 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 measurements. Furthermore, continuous, rather than average, measurement of VO2 appears to give highly reproducible results.