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Chapter 6
category). Adolescents with at least one parent born outside the Netherlands, but inside Europe, were classified as western immigrants (western category). An adolescent with at least one parent born in a foreign country outside Europe is considered to be of foreign non-western ethnicity (non-western category). The subjects were measured between November 2006 and August 2008. The study was approved by the Medical Ethics Committee of the VU University Medical Center Amsterdam.
Indirect calorimetry and body composition
The indirect calorimetry measurements were performed with a ventilated-hood system (Vmax Encore n29; Viasys Health Care, Houten, the Netherlands). The Vmax system was calibrated daily for flow. Also, the system is calibrated daily with 2 different standard gases (1: with 26% O2 and 0%CO2 and 1: with 16%O2 and 4% CO2) immediately before use and every 5 minutes during the measurement. Oxygen analyzer sensitivity is checked yearly by supplier. Measurements were standardized by internal guidelines. The subjects were in the supine position and awake and had fasted overnight. Data from the first 5 minutes of the measurements were removed. Oxygen consumption and carbon dioxide production were measured, and energy expenditure was calculated by using the Weir formula (16). The acceptable coefficient of variation was 10%. The measurements took place for 30 min. Body composition was assessed by Dual Energy X-ray Absorptiometry (DXA; Hologic QDR4500-Delphi, software 12.3.3. S/N 45665; Tromp Medical, Castricum, the Netherlands). The subjects were scanned for 10 min while wearing underwear and lying in a supine position with arms not touching the trunk and legs not touching each other. The DXA method measures bone mineral content, lean tissue mass, and fat mass (FM). In the present study fat-free mass (FFM) was defined as bone mineral content + lean tissue mass.
Body weight was measured (with subjects wearing underwear) and recorded within 0.1 kg with a calibrated electronic flat scale (SECA 861; Schinkel, Nieuwegein, the Netherlands). Height was measured and recorded with an accuracy of 1 mm with an electronic stadiometer (KERN 250D; De Grood Metaaltechniek, Nijmegen, the Netherlands). Weight and height were used to calculate BMI (weight in kilograms divided by the square of height in m). BMI standard deviation score (BMIsds) was calculated with the Growth Analyser (www.growthanalyser.org; version 3.5; reference Dutch population 1997).
REE predictive equations
Pubmed was used to conduct a systematic search for publications on Mesh- derived keys ‘energy metabolism’, ‘energy expenditure’, ‘basal metabolism’, and additional terms (‘predict*’, ‘estimat*’, ‘equation*’, and ‘formula*’) in every possible combination. Applied limitations were ‘English language’, ‘humans’, not ‘critical illness’, and ‘intensive care’. More references were obtained by screening
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