Abstract Body (Do not enter title and authors here): Background: Estimated cardiac output using the Fick principal (estFickCO) frequently informs clinical decision making in Cardiology Intensive Care Units (CICU). Assessment of estFickCO relies on estimation of resting oxygen uptake (rVO₂). We hypothesized that large variance will be present between rVO₂ measured with a metabolic cart and the estimated rVO2 often used in CICUs.

Methods: In this single-center study, 275 CICU patients with pulmonary arterial catheters in place to guide heart failure management underwent breath-by-breath metabolic cart measurement of rVO₂ for 10 minutes coupled with duplicate measures of arterio-venous oxygen content to derive Fick CO. Four equations to estimate rVO₂ were evaluated: weight-based only (3.5ml/kg/min, 1 MET); accounting for sex and BSA (Dehmer); sex, BSA, and age (Bergstra); and sex, BSA, age, and heart rate (LeFarge). Bland-Altman analysis and derivation of coefficients of variation were performed to evaluate the agreement between each equation and actual measured rVO₂.

Results: In this cohort of 275 patients (age 57.8±14.4, 24% female, BMI 28±6.9 kg/m²) the mean measured rVO₂ was 276±71 mL/min and Fick CO was 4.7±1.6 L/min. Using 1 MET to estimate rVO₂ equated to a mean rVO₂ of 292±81 mL/min, the Dehmer equation estimated a mean rVO₂ of 283±49 mL/min, Bergstra estimated a mean rVO₂ of 248±37 mL/min, and the LaFarge equation estimated a mean rVO₂ of 239±53 mL/min. The frequency of error being >25% was calculated at 24%, 15%, 17%, and 19% respective to each equation. When analyzed using Bland-Altman plots, the Dehmer equation demonstrated the lowest mean bias as well as the lowest coefficient of variation when compared to the other three estimates (Figure) yet limits of agreement span VO₂ values associated with > 3 L/min differences in Fick CO across all 4 estimates.

Conclusion: Measured VO₂ varies significantly from estimated VO₂ among CICU patients. Accounting for sex and BSA with use of the Dehmer equation was associated with the closest approximation of actual VO₂ values among 4 estimates analyzed in our study. High variance in rVO₂ estimates and impacts on management should be considered when interpreting estFickCO in CICU patients.