Fluid volume changes during hemodialysis monitored with the impedance technique

A fluid monitor based on the tetrapolar impedance technique was employed for continuous measurements of fluid volume change during hemodialysis treatment and compared to concomitant ultrafiltration and bed scale readings. Oral fluid intake before and during the dialysis immediately could be recorded with the bed scale as a weight change. In the readings of the fluid monitor, however, the response to fluid intake could be recorded only gradually, as the fluid was absorbed from the gastrointestinal tract. Taking this into account, together with a previously described artifact due to shifts in body position, an excellent agreement was obtained between impedance and bed scale fluid volume monitoring. It is concluded that impedance measurements give a better estimation of the amount of metabolically active fluid than does body weight monitoring.