Extracellular Water: Sodium Bromide Dilution Estimates Compared With Other Markers in Patients With Acquired Immunodeficiency Syndrome

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Abstract
Extracellular fluid and closely related extracellular water (ECW) provide information on nutritional status in health and disease. Although various methods exist for ECW determination, little is known about their comparability in patients with wasting diseases such as acquired immunodeficiency syndrome (AIDS). One practical method, the dilution of sodium bromide (NaBr), is used widely in clinical research, although its relationship to other ECW markers has not been well characterized. The present study sought to compare ECW estimates as determined by NaBr and three other methods in 11 male patients with AIDS (mean ± SD; age, 44 ± 12 years; body weight, 64.5 ± 8.8 kg; and height, 172 ± 4 cm) . ECW volumes were determined from NaBr dilution, total body chlorine (TBC1) by delayed γ-neutron activation analysis, total body water (TBW) by tritium dilution combined with total body potassium (TBK) by whole body 40K counting, and radioactive sulfate dilution ( 35SO4). All correlations between the NaBr method and other methods were statistically significant (NaBr vs TBC1 [r = .91; p < .001]; vs TBW/TBK [r = .76; p < .01]; and vs 35SO4 [r = .89; p < .001]). As expected from previous studies, ECW (L) derived by NaBr provided a group mean (15.1 ± 2.2 L) similar to the TBC1 method (15.4 ± 1.7 L; p = .32), a significantly smaller ECW than by the TBW/TBK method (18.6 ± 3.4 L; p = .0004) , and a significantly larger ECW than by 35SO4 method (13.3 ± 3.0 L; p = .002). Estimating ECW by NaBr dilution was comparable with other research-based ECW methods and, thus, offers a practical alternative for evaluating ECW in patients with AIDS. (Journal of Parenteral and Enteral Nutrition 23:61-66, 1999)