Handling
Q. Where can I measure?
A. Measurements can be performed just as easily at the bedside as during the regular patient consultation with the physician.
Q. When should I measure?
A. BCM measurements should be performed whenever dry weight needs to be determined, e.g. in case of
change to the medication or other clinical
intervention
the occurrence of symptoms,
perceived changes in body composition/lifestyle
hospitalization
Measurements should be performed pre-treatment, before cannulation. Post dialysis measurements may be obtained after 30 minutes of fluid re-equilibration.
Q. How often can I measure?
A. You can measure as often as you wish! There is no limitation; although dependent on patient condition the following is suggested:
Pre-ESRD: quarterly
HD: every 2nd week
PD: monthly (according to K/DOQI)
Acute patients: daily
Q. How long does a measurement take?
A. The measurement takes about 20 seconds. The results are displayed after about 1 min
Q. Can my patient sit during measurement?
A. Measurements are best performed with patient in a relaxed, supine position. The patient may also sit during measurement, but feet should be raised in order to achieve an equal distribution of fluids.
Q. How can I improve measurement quality?
A. Ensure patient is relaxed in the supine position
Ensure skin is clean and good electrode contact has been achieved
Check correct electrode placement
Check correct connection of patient lead
Try to minimize sources of electrical disturbances (power sources, mobile phones etc.)
Ensure legs are apart and arms are not in contact with the trunk.
Q. What is the impact of entering the wrong height? What is the effect of nude weight and clothed weight?
A.
Technology
Q. What is the difference between single frequency bioimpedance analysis (SF-BIA), multi frequency BIA (MF-BIA) and bioimpedance spectroscopy (BIS)?
A. Most single frequency devices (SF-BIA) (and fat scales) measure only at 50 kHz and therefore measure impedance which is influenced by a combination of ECW and ICW.
There are multi frequency devices (MF-BIA) that measure from 3 to 8 frequencies (between 5-800 kHz), but these devices allow also no accurate differentiation between ECW and ICW. MF-BIA uses empirical linear regression models to evaluate FFM, TBW, ICW and ECW that usually only apply to healthy subjects.
Bioimpedance spectroscopy (BIS) uses physiological modeling and mixture equations (Cole–Cole plot and Hanai formulae) to first determine the electrical resistance of ECW and ICW and then calculate the volumes of these respective compartments. This is essential for identification of OH – the BCM – Body Composition Monitor uses the BIS technique.
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Background Information
Q. Why do we need a body composition model?
A. The body composition model describes the intra and extracellular water content of lean tissue mass (LTM), adipose tissue mass (ATM) and excess fluid (overhydration, OH). LTM, ATM and OH are obtained from measurements of body weight, height and whole body intracellular water (ICW) and extracellular water (ECW) determined by bioimpedance spectroscopy. The body composition model determines whether changes in intra- and extracellular water reflect increase or loss of ATM or LTM.
Q. How are the output parameters validated?
A. The determination of fluid volumes has been validated against "gold standard" reference methods:Extracellular water – bromide dilutionIntracellular water – total body potassium (TBK)Total Body Water – deuterium dilution Lean Tissue Mass – Dual Energy X-ray Absorptiometry (DEXA)Adipose Tissue Mass – 4- compartment modelling, DEXA, Air displacement plethysmography and under water weighing Body Cell mass – magnetic resonance tomography, TBKThere is no existing gold standard reference for the determination of OH, but a high agreement has been demonstrated in comparison with expert clinical assessment and the comparison to the ultrafiltration volume withdrawn during a hemodialysis treatment
Q. When I drink 1 liter of water why don’t I see that in the measurement?
A. The BCM – Body Composition Monitor performs whole body measurements and is particularly sensitive to fluid accumulation in the limbs. It detects fluid almost entirely on a tissue level and in the blood vessels. As fluid is the best electrical conductor in the body, a volume of fluid with large cross sectional area has little influence on the measured whole body impedance. The trunk for example contributes as little as 10% to the whole body impedance. Consequently, in PD patients it makes little difference whether the measurements are made before or after drain out as the filling of the peritoneum will have virtually no effect on the calculation of overhydration. However the weight of the patient will be directly affected, thus influencing the calculation of body composition. It is advisable therefore that the weight obtained with an empty peritoneum is entered into the device.
Q. How is OH calculated?
A. The BCM - Body Composition Monitor expresses the body weight in terms of lean tissue mass (LTM – mainly muscle), adipose tissue mass (ATM – mainly fat) and overhydration (OH). Each of these compartments has a specific composition and contains a known quantity of water per mass of tissue. OH is almost 100% extracellular water, whereas the water of LTM and ATM consist of differing proportion of extracellular and intracellular water in addition to solid components. Healthy individuals are considered to be “normally hydrated" and therefore have virtually no overhydration. These individuals may be characterized in terms of ATM and LTM only. However, in pathophysiological conditions the presence of excess fluid that may accumulate has to be taken into consideration. Excess fluid represents an expansion of only the extracellular water, whereas ICW remains unchanged. The excess fluid may reside within adipose tissue or lean tissue raising the hydration of the respective tissue above the “normal” values (e.g. oedema). Alternatively, excess fluid may simply appear as a distinct compartment without altering the hydration of the major tissues (e.g. ascites, pleural effusion). As the extracellular hydration of LTM and ATM is known, the expected “normal” volume of ECW of these tissues can be calculated. The difference between "normal" ECW and measured ECW is the excess fluid, OH.
Q. What does negative OH mean?
A. Negative OH means that the patient is under- or dehydrated. This might be accompanied by increased frequency of intradialytic symptoms.
Q. What is the basis of the reference ranges?
A. Reference ranges are available for overhydration (OH), lean tissue index (LTI), fat tissue index (FTI) and E/I ratio. The reference ranges are defined by a reference population of 1000 healthy subjects between 18 and 75 years with a BMI between 18 - 32 kg/m2.The reference ranges are defined by the 10th and 90th percentiles of the reference population and are specific to age and gender. These ranges simplify identification of abnormal conditions by comparing a patient’s data to the reference population.
Q. Why do patients with artificial joints, amputations, stents, pregnancy, and pacemaker need to be excluded?
A. The BCM - Body Composition Monitor cannot be used in patients with stents or pacemakers (defibrillators) for safety reasons. Performance can be affected by artificial joints, pins or amputations.
Limitations
Q. Can I measure regional differences in body composition and fluid status?
A. The BCM - Body Composition Monitor performs whole body measurements between hand and foot and therefore cannot assess regional differences in body composition and fluid status. The device only detects interstitial fluid - a volume of fluid with a large crosssectional area has little influence on the whole body impedance.
Q. Can I measure in the ICU setting?
A. No, currently the BCM - Body Composition Monitor has no approval for ICUs (electrical safety, conformity), but this will be realized in the future.
Q. Why do patients with artificial joints, amputations, stents, pregnancy, and pacemaker need to be excluded?
A. The BCM - Body Composition Monitor cannot be used in patients with stents or pacemakers (defibrillators) for safety reasons. Performance can be affected by artificial joints, pins or amputations.
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