Effect of Body Mass Index Category on Body Surface Area Calculation in Children Undergoing Cardiac Procedures

BACKGROUND: Many of the common equations used for body surface area determination were either introduced before the widespread prevalence of childhood obesity, contained very few children in their sample, or have not been assessed in overweight/obese children. Therefore, we compared 6 body surface area formulae to determine their performance across body mass index categories using cross-sectional anthropometric data of children who underwent elective cardiac procedures. METHODS: We selected 6 formulae from the literature that included data from pediatric subjects in their derivation. We then substituted measured height and weight into each equation to compute body surface area data for the study subjects. The average values of the 6 formulae were calculated for each patient and used as reference for comparison. Comparisons between each formula and the reference standard were made with the 1-way ANOVA, Pearson correlation coefficient (measure of precision), the Lin concordance correlation coefficient (measure of bias and precision), and the Bland-Altman limit-of-agreement. All comparisons were made across age, sex, and body mass index categories. RESULTS: Among the 1000 (mostly Caucasian: 76.1%) subjects, 16.7% were overweight, while 14.1% were obese and 51.2% were girls. All calculated body surface area data showed a strong positive correlation with each other and the derived reference body surface area values (0.99–1.00; P < .001). Calculated body surface area values for all the formulae were significantly higher in overweight and obese children across every age group. CONCLUSIONS: Obesity status is a critical factor in the determination of body surface area values in children undergoing elective cardiac procedures. We caution that indexed hemodynamic and other therapeutic interventions may be inappropriate if limitations of body surface area formulae and the effect of obesity are not taken into consideration when caring for overweight and obese children. Body surface area studies utilizing accurate contemporary techniques that include sufficient number of overweight and obese children of various races are urgently needed.