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Keywords:

  • oxygen consumption;
  • Fick equation;
  • aortic stenosis;
  • elderly

Background

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.

Methods

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.

Results

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.

Conclusions

When estimating VO2 in an elderly population with aortic stenosis, the best equations are 2.5*Weight and 100*BSA. © 2013 Wiley Periodicals, Inc.