Application of bioelectrical impedance to clinical assessment of body composition in peritoneal dialysis.

Patients on peritoneal dialysis (PD) develop complex changes in body composition. These changes reflect hydration, nutrition, and body fat, all important elements reflecting patient well-being and efficacy of therapy that should be assessed and monitored as guides to patient management. They are all notoriously difficult to accurately measure in clinical practice and simultaneous abnormalities may obscure detection, as in the malnourished fluid-overloaded patient where body weight is misleadingly stable. Malnutrition is a serious complication in PD that carries an adverse prognosis. Assessment of hydration in PD is important in determining "dry weight" to allow adjustment of dialysis prescription to optimize fluid balance. A number of techniques have been investigated to measure body composition in clinical practice. Of these, bioelectrical impedance analysis (BIA) has attracted most interest and seems to be of greatest promise. Cases illustrating different aspects of the use of BIA in PD patients are described, and the background, possible uses, and limitations of BIA in PD patients are discussed. To be of clinical value, BIA must be used to distinguish between extracellular water (which reflects hydration) and body cell mass, or intracellular water (which declines in wasting and malnutrition). The high precision of BIA is ideally suited to detecting changes in body composition and its main role may be in longitudinal monitoring. However, inaccuracy of absolute measurements and variability of normal values in the general population make precise diagnosis of the degree of normality of body composition in an individual subject a more difficult task for body composition analysis.