Inaccuracy of Estimated Resting Oxygen Uptake in the Clinical Setting

Abstract

Hence, we assessed the accuracy of estimated resting VȮ 2 compared with measured VȮ 2 obtained by the gold-standard analysis of timed collections of exhaled air by the method of Douglas in a large population of consecutive adult patients who underwent right-heart cardiac catheterization for clinical indications at our hospital. Clinical Perspective on p 210Background-The Fick principle (cardiac output = oxygen uptake (VȮ 2 )/systemic arterio-venous oxygen difference) is used to determine cardiac output in numerous clinical situations. However, estimated rather than measured VȮ 2 is commonly used because of complexities of the measurement, though the accuracy of estimation remains uncertain in contemporary clinical practice. Methods and Results-From 1996 to 2005, resting VȮ 2 was measured via the Douglas bag technique in adult patients undergoing right heart catheterization. Resting VȮ 2 was estimated by each of 3 published formulae. Agreement between measured and estimated VȮ 2 was assessed overall, and across strata of body mass index, sex, and age. The study included 535 patients, with mean age 55 yrs, mean body mass index 28.4 kg/m 2 ; 53% women; 64% non-white. Mean (±standard deviation) measured VȮ 2 was 241 ± 57 ml/min. Measured VȮ 2 differed significantly from values derived from all 3 formulae, with median (interquartile range) absolute differences of 28.4 (13.1, 50.2) ml/min, 37.7 (19.4, 63.3) ml/min, and 31.7 (14.4, 54.5) ml/min, for the formulae of Dehmer, LaFarge, and Bergstra, respectively (P<0.0001 for each). The measured and estimated values differed by >25% in 17% to 25% of patients depending on the formula used. Median absolute differences were greater in severely obese patients (body mass index > 40 kg/m 2 ), but were not affected by sex or age. Conclusions-Estimates

Clinical Evaluation and Management of Pulmonary Hypertension in the Adult With Congenital Heart Disease

“…First, the Fick principal is often applied to determine cardiac output by the use of an estimate of O 2 uptake. This introduces important error, and O 2 uptake should be measured directly at the time of catheterization 17,18 ; dilution methods are appropriate only in the absence of intracardiac shunting. Second, catheterization data represent a snapshot of supine resting hemodynamics at a single moment in time.…”

Right heart catheterisation: best practice and pitfalls in pulmonary hypertension

“…Specifically, applying the indirect Fick technique leads to a high likelihood of inaccuracy in cardiac output, as results are frequently based on estimated values (rather than direct measurements) for oxygen uptake due to the time-consuming nature of the measurement and the expensive equipment required for the direct method [3,33]. This was clearly illustrated in a study of 535 adult patients undergoing RHC in whom resting oxygen uptake was assessed using estimated values according to three published formulae, or by direct assessment through timed collections of exhaled air via the Douglas bag technique [33]. Results from the study demonstrated a >25% difference between directly measured and estimated values in 17-25% of patients, depending on the formula used to derive the estimated values [33].…”

“…This was clearly illustrated in a study of 535 adult patients undergoing RHC in whom resting oxygen uptake was assessed using estimated values according to three published formulae, or by direct assessment through timed collections of exhaled air via the Douglas bag technique [33]. Results from the study demonstrated a >25% difference between directly measured and estimated values in 17-25% of patients, depending on the formula used to derive the estimated values [33].…”

Oxygen consumption in children and adults with congenital and acquired heart disease: the quest for better estimates: Table 1

“…Numerous studies demonstrated limited agreement of direct VO 2 measurements with VO 2 estimations 5 6. It has therefore been argued that VO 2 should always be measured and not estimated.…”