Identifying body fluid distribution by measurning electrical impedance

The effects of critical illness on extracellular water (ECW) and total body water (TBW) were measured using (1) a multiple dilutional technique, and (2) whole body and regional bioelectrical impedance anaysis (BIA) in a group of stable patients. Total body water and body resistance (R) were similar in patients when compared with normal healthy subjects (TBW:45.1 ± 4.5 vs. 46.2 ± 3.4 L, ρ = 0.85; R: 518 ± 42 vs. 500 ± 22Ω, ρ=0.70), and a significant relationship was present between these measurements (r = −0.87, p < 0.001). However, patients demonstrated an increase in ECW compared with controls (ECW: 18:6 ± 1.3 vs. 14.7 ± 1.1 L, p < 0.05). Expanded ECW values were associated with diminished electrical reactance (X_c) values (38± 6 vs. 70 ± 4, p < 0.001) and these values were correlated (r = −0.67, p < 0.005). The ratio of X_cto R determined across the body and each of the segments was significantly lower in patients compared with controls (at least p < 0.005) and this ratio measured across a leg was the most sensitive predictor of health (X_c/R ± 0.137) and disease (X_c/R ± 0.101). Bioelectrical impedance analysis is a noninvasive and simple beside technique that can be used to predict TBW and identity altered fluid distribution following critical illness.