Objectives: No gold standard for ideal body weight determination in children exists. We aimed to compare four methods of ideal body weight calculation and determine level of agreement between methods and impact of measurement variance on tidal volumes prescribed in mechanically ventilated pediatric acute respiratory distress syndrome.
Design: Post hoc analysis of four multicenter pediatric acute respiratory distress syndrome studies.
Setting: Twenty-six academic PICUs.
Patients: Five hundred eighty-nine patients.
Interventions: None.
Measurements and main results: Ideal body weight was calculated by four common methods: National Center for Health Statistics, McLaren, Moore, and body mass index, and compared in three ways: 1) determine the proportion of the cohort for which each method could successfully calculate ideal body weight; 2) compare the level of agreement between the ideal body weight methods by Bland-Altman analysis; and 3) evaluate the difference in tidal volume when 6 mL/kg ideal body weight was prescribed. We a priori defined the better method to be one that could calculate ideal body weight in most subjects, had good agreement with other methods, and led to a lower tidal volume. Only 55% could have ideal body weight measured by all four methods. National Center for Health Statistics, McLaren, and Moore methods could calculate ideal body weight in greater than or equal to 90%, whereas body mass index method was successful in only 61% because of no body mass index validation in less than 2-year-olds. In comparing each method to the others, there was great variance, particularly in greater than or equal to 10-year-olds. This variance was greatest between Moore and body mass index methods with greater than or equal to 10 kg difference in ideal body weight in some subjects. The McLaren method had the best agreement with all other methods, and yielded similar prescribed tidal volume in 2- to 10-year-olds and lower tidal volume in greater than or equal to 10 years old.
Conclusions: There is substantial variation in calculated ideal body weight among four commonly used methods, particularly in adolescents. Since varying ideal body weight may lead to discrepancies in pediatric acute respiratory distress syndrome care, a standard approach to ideal body weight measurement is needed. We recommend the McLaren method to calculate ideal body weight in children with pediatric acute respiratory distress syndrome until a gold standard method is validated.