The 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.

Vo₂ 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.

A 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).

The 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.