SUN-285 LIMITATIONS OF BIOIMPEDENCE SCALES IN MEASURING FLUID GAINS IN DIALYSIS PATIENTS, HOME MACHINES VS STANDARD MACHINES

Abstract

Ideal body weight (IBW) has often been estimated by bioimpedence methods. Calf bioimpedance scales (cBIS) have been suggested as an accurate way of measuring fluid content of the body, but only a few studies have been done which have not demonstrated mortality benefits. Bioimpedance techniques have been shown to provide an accurate reference for the estimation of dry weight in numerous studies in HD but the method involves expensive machines with facility for multichannel readings to estimate fat, fluid, muscle and bone content of body. Home body analysis scales, that use bioimpedance methods have been available in the market, this measures the resistance to current flow through the feet alone and gives estimates of the persons body content and recent machines can store data of multiple patients. This study aims to assess the clinical significance of the hydration status estimated by simple home body analysis scale (BAS), whether this can be an assisting clinical tool in achieving normal fluid status in dialysis patients and explore the limitations of this method. We also did a comparison using a control with standard bioimpedence scales (Tanita models TIMC 780 MA, and TIDC-360) We selected 8 stable patients receiving in-centre haemodialysis at Renal Unit, Tamworth Base Hospital. Patients under the age of 75, who can stand up for weight assessment, who is willing to take the socks off for bioimpedance measurement are included. The study was conducted over two weeks, six dialysis sessions for each patient. We assumed that a 1 kg weight reduction during a haemodialysis treatment represents a 1 L reduction in body fluid volume. Fat and muscular components of body composition are assumed to stay constant over the course of the study. The details of ultrafiltration volume (UFV) and amount of water, fat, bone and muscle percentage pre and post dialysis shown on BAS were recorded. We also checked 4 normal subjects (authors of the study) who checked their body indices before and one hour after drinking a litre of water to see how the machine read the changes. We did a comparison of water loading on two models of Tanita (models TIMC 780 MA, and TIDC-360) Three patients have consistently shown error due to percentage relative to bodyweight even though they were not clinically obese. In five patients, weight reduction was accurately captured by the machine post dialysis, but the reduction was shown in the fat compartment and not the fluid compartment as expected. The control subjects too, showed weight gain in the fat compartment and not the fluid compartment after water ingestion. This same error was found in the Tanita machine with the control showing weight gain in the fat compartment after water ingestion. The standard machine was not tested in the dialysis patients as we did not have access to multichannel bioimpedence machines in our unit. Both the expensive multichannel machines and the home bioimpedence scales showed same error in controls after fluid ingestion, with fluid gain recorded in the fat compartment. In dialysis patients, post dialysis fluid loss was recorded as reduction in the fat content, not fluid content (using home bioimpedence scales). Literature search has not revealed details of the body compartment from where the fluid was removed. Fluid storage in dialysis patients needs further study.