Estimation of extracellular space and blood volume using bioelectrical impedance measurements

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 (Xc) from bioelectrical impedance measurements were used to obtain multiple regression equations for ECS and BV. The variables weight, gender, and height 2/Xc were independent predictors of ECS (r = 0.767; P less than 0.0001). Height 2/R and gender were predictors of blood volume (r = 0.856; P less than 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 +/- 3.08 l or 19.6% of the mean Br space of 15.7 l. 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.