Estimation of oxygen consumption in elderly patients with aortic stenosis

Invasive evaluation of aortic stenosis requires measuring cardiac output. With the Fick equation, a measure of oxygen consumption (VO₂) is required. Standard equations for estimating VO₂ were derived in younger and healthier populations than the ones referred for possible transcatheter aortic valve replacement. The goal of this study was to determine the best method of estimating VO₂ in elderly patients with aortic stenosis.

We directly measured VO₂ in elderly patients undergoing invasive assessment of aortic stenosis. We compared standard equations estimating VO₂ and two prespecified hypothesized equations for VO₂ to determine which was most accurate. We also examined the subgroup of patients with low flow.

Among 51 patients, aged 80-97 years, the mean VO₂ was 198 mL/min. Using 125*body surface area (BSA) to estimate VO₂ the average error was 35 mL/min, and 67% of values were within 25% of the true value. Using 3*Weight to estimate VO₂, those numbers were 29 mL/min and 65%. The hypothesized equations did better: 100*BSA had error of -12 mL/min and 90% within 25% of measured VO₂; for 2.5*Weight it was -9 mL/min and 84%. Among the 20 patients with low flow, hypothesized equations performed best. Using 2.5*Weight and 100*BSA there were 90% and 85% within 25% of measured VO₂, respectively, compared to 55% and 75% when 3*Weight and 125*BSA were used. Weight and BSA were the only independent predictors of VO₂.

When estimating VO₂ in an elderly population with aortic stenosis, the best equations are 2.5*Weight and 100*BSA.