生体インピーダンスと血漿膠質浸透圧の同時計測による生体内水分量の推定

抄録

The body water (extracellular fluid volume) of a healthy person with constant electric resistivity (47Ω · cm) can be estimated by a body-fat meter using the bioimpedance method. However, for dialysis patients, for whom the management of extracellular fluid volume is very important, accurate estimation is not possible because of individual variation in resistivity depending on kidney function and accumulation of body water. In this study, we investigated the usefulness of a simple method for determining electric resistivity in dialysis patients. Since Posm does not change in ECUM (Extracorporeal Ultrafiltration Method) therapy, which removes only moisture and low molecular weight solute by ultra-filtration, change in extracellular fluid volume can be computed by change in the colloid osmotic pressure with a body water movement model. Experimentally, we measured the serous colloid osmotic pressure and impedance in various parts of the body (right arm, left arm, soma, right leg, left leg) of patients undergoing ECUM treatment. Then we estimated extracellular fluid volume changes using the body water movement model and the amount of fluid removal and serous colloid osmotic pressure measured from the blood. The electric resistivity for each patient could be calculated from the extracellular fluid volume and the impedance in each body part. Using the electric resistivity calculated for each patient, extracellular fluid volume can be estimated by simply measuring the living body impedance. In other words, since the excess and deficiency of body water can be measured quantitatively, it can be used for setting the tolerable level of fluid intake and standard body weight during dialysis. Moreover, extracellular fluid volume can be roughly estimated using the approximate electric resistivity calculated using only the set fluid removal quantity and the measured impedance of each body part in ECUM therapy. Thus, a body water meter specific to each dialysis patient can be made by carrying out ECUM therapy only once and determining the approximate electric resistivity from living body impedance measurement and the set fluid removal quantity and incorporating the approximate value into the so-called body-fat meter.