BackgroundThe LaFarge equation is the most commonly used equation to estimate oxygen consumption (Vo2) in patients of all ages with congenital heart disease, although it was generated in patients older than 3 years. We sought to determine the validity of the LaFarge equation in estimating Vo2 in children younger than 3 years undergoing cardiac catheterization with general anesthesia.MethodsVo2 was measured directly using respiratory mass spectrometry in 75 sedated, paralyzed, and mechanically ventilated children in the pediatric cardiac catheterization laboratory. Age ranged from 0.13 to 24 years; 40 children being younger than 3 years. Estimated values for Vo2 were calculated using the LaFarge equation for all patients. The agreement between measured and estimated Vo2 was evaluated by the bias and limits of agreement in the 2 age groups. Regression analysis was used to analyze the influence of age on the agreement.ResultsA failure of agreement between measured and estimated Vo2 was noted in both groups of children. As compared to the older group of patients, the agreement was significantly poorer in children younger than 3 years, with a significantly greater overestimation introduced by the LaFarge equation (11% ± 21% vs 53% ± 52%, P < .0001).ConclusionThe LaFarge equation introduces significant error in the estimation of Vo2 in ventilated patients with congenital heart disease of all ages, particularly in children younger than 3 years.
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