Bioimpedance Spectroscopy (BIS): Fluid Changes in Hemodialysis Patients

Hemodialysis

hemodialysis, bioimpedance, absolute blood volume, total body water, extracellular body water, intracellular water, body weight

In connection with dialysis treatment, fluid and salt balance changes. Some kidney disease patients experience fluid accumulation in the body and need to have excess fluid removed via the dialysis machine. Others have too little fluid in their bodies and experience general symptoms. The amount of fluid that needs to be removed is an individual assessment and can be difficult to determine. Today, fluid removal is determined based on signs such as water in the lungs, swollen legs, and blood pressure. By using a so-called bioimpedance spectroscopy (BIS) device, it os possible measure how much fluid is in the body. However, the calculations that BIS devices use are developed for healthy individuals and do not work optimally during dialysis. Therefore, the investigators will use the actual measurements and compare them with fluid extraction and weight changes to examine their relationship. Hemodialysis patients with ultrafiltration on 3 consecutive dialysis days in order to investigate whether there is a difference in measurements after the long dialysis break and whether the measurements are the same when you are being drawn to your dry weight are included. Other patients without fluid removed during dialysis will be investigated once. I the study the absolute blood volume is also measured, that is, how much fluid is in the bloodstream. This is also an expression of the body's total fluid volume. By combining the various measurements, the study will gain increased knowledge about your hydration status. If the measurement methods have sufficient precision, the use of BIS and measurement of total blood volume may contribute to a more accurate determination of your dry weight.

To investigate whether raw impedance data from BIS measurements can be used as a tool to estimate changes in fluid status in HD patients. Accuracy is low when using prediction equations that are integrated into the individual BIS device. This challenges the application in clinical practice. Furthermore, the prediction equation is not available for most devices. Small studies suggest greater accuracy when using raw data, which could make BIS measurements clinically applicable. Detailed purpose. To examine whether raw impedance data from BIS measurements can be used as a tool to estimate changes in fluid status in HD patients. 1. Ensure consistency in measurements of raw impedance data (Phase angle, RE, RI, R∞, and Cm) between different BIS devices (here: Fresenius BCM®, SFB7®, and SOZO® from ImpediMed). 2. Compare intradialytic ∆RE, ∆R∞, and ∆Cm against changes in absolute blood volume, BP, weight, and fluid removal in HD patients with fluid removal. 3. Is the phase angle consistent over the 3 dialysis days in a week for center dialysis patients with fluid retention? 4. Compare intradialytic ∆RE, ∆R∞, and ∆Cm against changes in absolute blood volume, blood pressure, and weight in hemodialysis patients without fluid retention. 5. Compare intradialytic ∆blood pressure, ∆weight, ∆ABV, fluid retention, and BIS measured changes (∆RE, ∆R∞, ∆Cm) for patients undergoing home hemodialysis with patients undergoing center hemodialysis.

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