Related Experiment Videos
Comparison of extra-cellular fluid volume measurement in children by 99Tcm-DPTA clearance and multi-frequency
S W Smye1, H M Norwood, T Buur
1Department of Medical Physics, St. James's University Hospital, Leeds, UK.
Insights
Comparing isotope dilution and electrical impedance methods for estimating extra-cellular fluid (ECF) volume in children, this study found impedance measurements correlated well with isotope dilution. Both techniques showed significant agreement, suggesting impedance is a viable method for ECF volume assessment.
Area of Science:
- Biomedical Engineering
- Pediatric Physiology
- Medical Physics
Background:
- Accurate estimation of extra-cellular fluid (ECF) volume is crucial in pediatric care.
- Isotope dilution is a standard method for ECF volume measurement, but it involves radioactive tracers.
- Electrical impedance techniques offer a non-invasive alternative for assessing body composition and fluid volumes.
Purpose of the Study:
- To compare ECF volume estimates derived from isotope dilution with those obtained using whole-body electrical impedance analysis in children.
- To evaluate the correlation and agreement between these two measurement techniques.
- To determine the efficacy of electrical impedance, incorporating frequency-dependent data and height-based models, in estimating ECF volume.
Main Methods:
- ECF volume was measured in 16 children using isotope dilution with 99Tcm-diethylene triamine penta-acetate (DPTA).
- Whole-body electrical impedance was measured across 50 frequencies (1 kHz to 1.348 MHz) and fitted to a three-element equivalent-circuit model.
- Two impedance-based ECF volume estimates (Vi1, Vi2) and a height-based estimate (Vh) were calculated and compared to the isotope dilution estimate (Vt).
Main Results:
- All impedance-based estimates (Vi1, Vi2, Vh) showed strong linear correlations with the isotope dilution estimate (Vt) (r² values of 0.98, 0.99, and 0.95, respectively).
- The agreement levels between techniques were within acceptable ranges, with Vi1 showing the closest agreement to Vt (+/- 0.95 L).
- Despite good correlations, differences between the techniques were not statistically significant, indicating comparable results.
Conclusions:
- Electrical impedance techniques, particularly when incorporating frequency-dependent data and anthropometric measures, provide reliable estimates of ECF volume in children.
- The findings support the use of non-invasive electrical impedance as a viable alternative to isotope dilution for ECF volume assessment in pediatric populations.
- Further research with more accurate and detailed measurement protocols is recommended to refine these 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.