A Comparison of Techniques in Assessment of Postdialysis Dry Weight: The Relationship Between Biochemical Markers(ANP and cGMP) and Multifrequency Bioelectric Impedance

Choi, Kyu Bok

Abstract

OBJECTIVE
The accurate evaluation of dry weight followed by hemodialysis is very important. So far, dry weight has been clinically estimated by using diagnostic parameters such as weight changes during dialysis, blood pressure, extremity edema, pulmonary edema, and chest X-rays. However, these methods result in frequent trials and errors because of the low accuracy. Recently, new methods have been attempted in a non-invasive way of determining dry weight. Bioelectric impedance method has been reported to be highly related to hemodynamic parameters before and after hemodialysis, and plasma atrial natriuretic peptide(ANP) and cyclic guanosine 3', 5'-monophosphate(cGMP) concentrations have been known to represent the amount of blood. In this study, we compared and analyzed the method of dry weight evaluation followed by hemodialysis by using multifrequency bioelectric impedance method(BIA method) and biochemical index(ANP method and cGMP method).
METHODS
Subjects consisted of seventeen patients who had received maintenance hemodialysis. Using multifrequency bioelectric impedance method before and after hemodialysis, a RTBW/RECF ratio in the right lower extremity was measured. Plasma ANP and cGMP concentrations were measured by collecting blood in arterial port.
RESULTS
1)Changes before and after hemodialysis: Post- dialysis weight decreased by 2.1+/-0.22kg. A RTBW/ RECF ratio significantly decreased from 0.3525+/-0.004 pre-dialysis to 0.3292+/-0.002 post-dialysis(p< 0.01). Plasma cGMP concentration(pmol/mL) significantly decreased from 23.9+/-4.4 pre-dialysis to 8.8+/-3.4 post-dialysis(p<0.01), and plasma ANP concentration(pg/mL) significantly decreased from 315+/-64 pre-dialysis to 222+/-71 post-dialysis(p<0.05). The extent of weight loss was not associated with above three parameters after dialysis. 2)The relationship between RTBW/RECF ratios and biochemical parameters:No relationship was noted between two parameters before dialysis, while a significant relationship was observed with plasma cGMP concentrations or plasma ANP concentrations after dialysis(r=0.705, p<0.01; r=0.653, p<0.01, respectively). 3)The measure of agreement in estimation of dry weight after dialysis(kappa value):Although the consistencies of a BIA method and a cGMP method were good(kappa=0.64), the consistency between a BIA method and an ANP method was low(kappa=0.21), and the consistency between a cGMP method and an ANP method was almost negligible(kappa=0.09).
CONCLUSION
In conclusion, RTBW/RECF ratio or plasma cGMP concentration can be used, but plasma ANP concentration is not suitable for evaluating dry weight after dialysis.