Validity of the LaFarge equation for estimation of oxygen consumption in ventilated children with congenital heart disease younger than 3 years—A revisit

BACKGROUND: The LaFarge equation is the most commonly used equation to estimate oxygen consumption (Vo(2)) 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 Vo(2) in children younger than 3 years undergoing cardiac catheterization with general anesthesia. METHODS: Vo(2) 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 Vo(2) were calculated using the LaFarge equation for all patients. The agreement between measured and estimated Vo(2) 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. RESULTS: A failure of agreement between measured and estimated Vo(2) 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). CONCLUSION: The LaFarge equation introduces significant error in the estimation of Vo(2) in ventilated patients with congenital heart disease of all ages, particularly in children younger than 3 years.