Estimation of total body water from foot-to-foot bioelectrical impedance analysis in patients with cancer cachexia - agreement between three prediction methods and deuterium oxide dilution

Rapid measurement of total body water to facilitate clinical decision making in hospitalized elderly patients

BACKGROUND

Bioelectrical impedance analysis (BIA) is a noninvasive rapid and simple bedside technique that can be used to predict total body water (TBW), extracellular water (ECW), and intracellular water (ICW) and identify altered fluid distribution following critical illness.

METHODS

An equivalence study of BIA in 32 hospitalized elderly patients was compared with reference standard dilutional measurements of deuterated water (TBW) and sodium bromide (ECW). The results were compared with anthropometric equations commonly used to predict TBW.

RESULTS

There was variability in TBW content among the participating hospitalized elderly patients. This variability was within (+/-5 L) and the percent difference between the standard and BIA was as follows: mean (range) -4.1% (-18.5 to 11.2). BIA reliably predicted TBW and ECW in individual participants, whereas standard prediction equations uniformly over- or underestimated TBW in individuals and whole group population.

CONCLUSION

TBW in hospitalized elderly patients can be estimated noninvasively by bedside BIA. Standardized anthropometric equations have to be used with caution in this population.

Implications of the variability in time to isotopic equilibrium in the deuterium dilution technique

OBJECTIVE

To investigate the variability in isotopic equilibrium time under field conditions, and the impact of this variability on estimates of total body water (TBW) and body composition.

DESIGN AND SETTING

Following collection of a fasting baseline urine sample, 10 women and 10 men were dosed with deuterium oxide (0.05 g/kg body weight). Urine samples were collected every hour for 8 h. The samples were analysed using isotope ratio mass spectrometry. Time to equilibration was determined using three commonly employed data analysis approaches.

RESULTS

Isotopic equilibrium was reached by 50, 80 and 100% of participants at 4, 6 and 8 h, respectively. The mean group equilibration determined using the three different plateau determination methods were 4.8+/-1.5, 3.8+/-0.8 and 4.9+/-1.4 h. Isotopic enrichment, TBW, and percent body fat estimates differed between early (3-5 h), but not later sampling times (5-8 h).

CONCLUSION

Although the three different plateau determination approaches resulted in differences in equilibration time, all suggest that sampling at 6 h or later will decrease the likelihood of error in body composition estimates resultant from incomplete isotopic equilibration in a small proportion of individuals.