NEW BIOELECTRICAL-IMPEDANCE FORMULA FOR PATIENTS WITH RESPIRATORY INSUFFICIENCY - COMPARISON TO DUAL-ENERGY X-RAY ABSORPTIOMETRY

Malnutrition in patients with severe respiratory insufficiency can lea d to severe complications, justifying the use of objective nutritional assessment techniques, such as bioelectrical impedance analysis (BIA) , which is an easy, noninvasive method of measuring body composition. The purpose of this study was to develop, and validate against dual-en ergy X-ray absorptiometry (DXA), a BIA formula to predict fat-free mas s (FFM) specific for patients with chronic severe respiratory insuffic iency. Seventy-five ambulatory patients (15 females and 60 males) with severe chronic respiratory insufficiency (obstructive and restrictive ) aged 63.6+/-19.2 yrs (mean+/-SD), in a stable pulmonary and cardiac condition for greater than or equal to 2 onths, were measured simultan eously with BIA and DXA. Patients younger than 45 yrs of age and with a body mass index greater than or equal to 32 kg.m(-2) were excluded. The best-fitting multiple regression equation to predict FFM = -6.06 (height x 0.283) + (weight x 0.207) - (resistance x 0.024)+ (sex (mal es=1, females=0) x 4.036), gave a correlation coefficient of r=0.952, slope+/-SEM 0.902+/-0.034, standard error of the estimate 1.670, and p <0.0001, The mean difference for FFM was 0.2+/-2.3 kg (mean+/- SD) and percentage fat mass was -0.7+/-3.8%. These results suggest that the b ioelectrical impedance analysis formula specific to patients with seve re respiratory insufficiency give a better correlation and smaller mea n differences than 12 different bioelectrical impedance analysis formu lae described in the medical literature. A prediction equation, valida ted against dual-energy X-ray absorptiometry and based on subjects wit h similar clinical characteristics, is more applicable to the patients with respiratory insufficiency than a formula developed for healthy s ubjects. (C) ERS Journals Ltd 1998.