Multifrequency bioelectrical impedance fails to quantify sequestration of abdominal fluid.

Multifrequency bioelectrical impedance analysis (MFBIA) was used to determine the intracellular (ICW) and extracellular water (ECW) compartments in rats. Resistance and reactance were measured on various body segments with frequencies ranging from 1 KHz to 1 MHz. After initial measurements, 0.9% NaCl was injected intravenously or intraperitoneally, and changes in ECW and ICW were estimated by MFBIA. Important differences were found between segments. In the leg, estimated ECW increased in proportion to the volume of intravenous fluid infused, whereas estimated ICW changed minimally. However, in the trunk region, both estimated ECW and ICW were increased with intravenous and intraperitoneal injections. Our findings indicate that MFBIA has important limitations for quantifying fluid compartments in the trunk and thus in whole body, especially when applied to ill patients in whom sequestration of fluid in the trunk region frequently occurs.