Estimation of extracellular space and blood volume using bioelectrical impedance measurements

Summary The bromide-82 dilution space (extracellular space, ECS) and blood volume (BV) were measured in 21 patients with esophageal and gastric cancer and in 27 patients 18–96 months after total gastrectomy. Resistance (R) and reactance (X_c) from bioelectrical impedance measurements were used to obtain multiple regression equations for ECS and BV. The variables weight, gender, and height ²/X_c were independent predictors of ECS (r = 0.767; P < 0.0001). Height 2/R and gender were predictors of blood volume (r = 0.856; P < 0.0001). The mean difference between the Br space and the ECS predicted from impedance measurements was 0 ± 1.54 (mean ± SD). The limits of agreement (± 2 SD) were therefore ±3.081 or 19.6% of the mean Br space of 15.71. The limits of agreement for BV were ±789 ml or ±19.7% of the average BV of 4008 ml. It is concluded that bioelectrical impedance plethysmography using a single frequency can be used for the estimation of ECS and BV The wide limits of agreement, however, may limit its used in clinical practice.Abbreviations ECS extracellular space - BV blood volume - R resistance - X_c reactance - SD standard deviation - LBM lean body mass - TBW total body water - RCM red blood cell mass - cAMA corrected arm muscle area - Z impedance - ANOVA analysis of variance - NS not significant - Na_e/K_c exchangeable sodium to exchangeable potassium ratio - p specific resistivity - PV plasma volume