Assessment of adult malnutrition and prognosis with bioelectrical impedance analysis: phase angle and impedance ratio.

Abstract

Malnutrition affects prognosis in many groups of patients. Although screening tools are available to identify adults at risk for poor nutritional status, a need exists to improve the assessment of malnutrition by identifying the loss of functional tissues that can lead to frailty, compromised physical function, and increased risk of morbidity and mortality, particularly among hospitalized and ill patients and older adults. Bioimpedance analysis (BIA) offers a practical approach to identify malnutrition and prognosis by assessing whole-body cell membrane quality and depicting fluid distribution for an individual. Two novel applications of BIA afford opportunities to safely, rapidly, and noninvasively assess nutritional status and prognosis. One method utilizes single-frequency phase-sensitive measurements to determine phase angle, evaluate nutritional status, and relate it to prognosis, mortality, and functional outcomes. Another approach uses the ratio of multifrequency impedance values to indicate altered fluid distribution and predict prognosis. Use of basic BIA measurements, independent of use of regression prediction models and assumptions of constant chemical composition of the fat-free body, enables new options for practical assessment and clinical evaluation of impaired nutritional status and prognosis among hospitalized patients and elders that potentially can contribute to improved patient care and clinical outcomes. However, these novel applications have some technical and physiological limitations that should be considered.