Comparison of Calculated with Measured Oxygen Consumption in Children Undergoing Cardiac Catheterization

Our objective was to compare calculated (LaFarge) with measured oxygen consumption (VO₂) using the AS/3 TM Compact Airway Module M-CAiOVX (Datex-Ohmeda, Helsinki, Finland; AS/3 TM) in children without cardiac shunts in a prospective, observational study. VO₂ was determined at the end of the routine diagnostic and/or interventional catheterization. VO₂ was calculated according to the formula of LaFarge and Miettinen for each child and compared with the measured VO₂. Data were compared using simple regression and Bland Altman analysis. Fifty-two children aged from 0.5 to 16 years (median, 6.9 years) and weighing 3.4 to 59.4 kg (median, 22.9 kg) were investigated. Calculated VO₂ values ranged from 59.0 to 230.8 ml/min, and measured VO₂ values from 62.7 to 282.2 ml/min. Comparison of calculated versus measured VO₂ values revealed a significant correlation (r = 0.90, p < 0.0001). Bias and precision were 8.9 and 48.3 ml/min, respectively (95% limits of agreement: −39.4 to 57.2 ml/min). Comparison of calculated VO₂ in children older than 3 years (n = 41), as restricted to the formula, with measured VO₂, revealed a slightly reduced correlation (r = 0.86, p < 0.0001). Bias and precision were 10.0 and 52.5 ml/min, respectively (95% limits of agreement: –42.4 to 62.5 ml/min). We conclude that calculation of VO₂ by the LaFarge formula does not provide reliable values compared to measured values. In clinical routine, measured rather than calculated VO₂ values should be used for the estimation of cardiac output and related variables.