Air Displacement Plethysmography is an Accurate and Feasible Non-invasive Measure of Fat-Free Mass in Children with Intestinal Failure.

BACKGROUND: The nutritional status of children with intestinal failure (IF) can be difficult to determine using body weight and currently available anthropometric techniques. Air displacement plethysmography (ADP) is a non-invasive measure of whole-body composition that measures body mass and volume, with a calculation of percent body fat (%BF) and fat-free mass (FFM) that may be useful during the provision of specialized nutrition.

OBJECTIVES: To evaluate the validity and feasibility of measuring body composition in children with IF using ADP compared with deuterium dilution, as well as secondarily with other measures of body composition, namely bioelectrical impedance analysis (BIA), dual-energy x-ray absorptiometry (DXA) and four-site skinfold anthropometry.

METHODS: We conducted a prospective cohort study of 18 children recruited through the Center for Advanced Intestinal Rehabilitation (CAIR) at Boston Children's Hospital. Patients 2-17 years of age with IF dependent on parenteral nutrition (PN) for more than 90 days were included. Spearman rank correlation and Bland-Altman limits of agreement (LOA) analysis were used to compare ADP to four alternative measures of body composition.

RESULTS: Eighteen children with IF, median age 7.1 (interquartile range (IQR) 5.4-9.3) years, 9 female (50%), and median residual bowel length 31 (IQR 22-85) cm were enrolled. Median PN energy intake was 46 (IQR 39-49) kcal/kg/day. Incomplete bladder emptying lead to invalid measures of deuterium dilution in 4 subjects. Spearman correlation coefficients for percent body fat (%BF) were low to moderate between ADP and deuterium dilution (r = 0.29), DXA (r = 0.62), BIA (r = 0.50) and skinfold (r = 0.40). Correlations for fat-free mass (FFM) were high between ADP and these other measures (range 0.95 to 0.98). Comparing ADP with deuterium dilution and skinfold measures, Bland-Altman analysis showed small mean bias (-1.9 and +1.5 kg) and acceptable 95% LOA ranges (10.7 and 22.9 kg), respectively, with larger bias (-10.7 and -7.7 kg) and LOA ranges (38.7 and 45.2 kg) compared to DXA and BIA. %BF by ADP and skinfold thickness were moderately correlated (r = 0.43) with low bias (-0.2%) but very wide LOA (25.7%).

CONCLUSIONS: Body composition via ADP is feasible and valid in children with intestinal failure as a measure of fat-free mass but appears less suitable for the measurement of percent body fat. The technique holds promise as a non-invasive measure of body composition to assess the efficacy of nutritional, medical and surgical interventions.