Comparison of extra-cellular fluid volume measurement in children by⁹⁹Tc^m-DPTA clearance and multi-frequency impedance techniques

Abstract

Comparisons of extra-cellular fluid (ECF) volume estimates made by isotope dilution and electrical impedance techniques have been made in a group of 16 children. For each patient an estimate of ECF volume (Vt) was obtained from measurements of the blood clearance of 99Tcm-diethylene triamine penta-acetate (DPTA) which was compared with two estimates (Vi1 and Vi2) of ECF volume obtained from measurements of the whole-body electrical impedance at 50 frequencies in the range 1 kHz to 1.348 MHz and a third estimate Vh based on patient height, L, alone. The observed frequency response of the impedance measurements was fitted to a three-element equivalent-circuit model of whole-body impedance and gave a value of the ECF resistance R. Vi1 was obtained from Vi1 = a (L2/R) + b. Vi2 was given by c(W1/2L2/R)2/3 where W is the patient weight, and Vh was given by dL2 + e. The constants a, b, c, d, e were determined by comparison with Vt and were equal to 0.335 l omega m-2 (standard error = 0.01 1 omega m-2), 0.42 l (0.25 l), 0.33 l (omega 2kg-1m-4)1/2 0.007 l (omega 2kg-1m-4)1/3, 4.92 l m-2 (2.8 x 10(-5) lm-2), 0.13 l (0.41 l), respectively. Vi1, Vi2, Vh were linearly correlated with Vt (r2 = 0.98, 0.99, 0.95, respectively, p < 0.001), and upper and lower levels of agreement were given by +/- 0.95 l (Vt and Vi1), 1.44 l and -1.12 l (Vt and Vi2), +/- 1.5 l (Vt and Vh), respectively. Thus inclusion of the impedance data accounted for greater volume variation, but differences between the techniques were not significant (paired t-test and Mann-Whitney analysis) suggesting that more accurate and detailed measurements are required.

Measurement of extracellular fluid volume in the neonate using multiple frequency bio-impedance analysis

“…The accuracy of such an approach in the neonate is open to question. Nevertheless, the application of this method in children as young as 8 months (Smye et al 1994) suggests that it may be worthy of further study in the neonate.…”

Comparison of bioimpedance and radioisotope methods in the estimation of extracellular water volume before and after coronary artery bypass grafting operation

“…The radioisotope dilution techniques and bioimpedance methods have often been compared to assess the accuracy of bioimpedance methods in body fluid volume estimations ( Kushner & Schoeller, 1986; Hannan et al ., 1994 ; Smye et al ., 1994 ; Patel et al ., 1996 ). An impedance index determined at low frequencies (5 kHz) correlates most closely with ECW volume ( Hannan et al ., 1994 ; Cha et al ., 1995 ).…”

Assessment of the sensitivity of bioimpedance to volume changes in body water

“…If during these episodes fluid movement occurred from the extracellular fluid into both the intracellular space and the ultrafiltrate, the recorded change in impedance would be larger than the actual change in TBW. This hypothesis may be tested using multifrequency techniques [14]. Also, recent work [15] has demonstrated that early versions of the Holtain impedance device are likely to incur errors in some patients (although this may be limited to adults).…”