Hemodialysis (HD) versus peritoneal dialysis (PD): latent overhydration in PD patients?

Data on the difference in fluid status between hemodialysis (HD) and peritoneal dialysis (PD) patients are scarce. Bio-electrical impedance analysis (BIA) is able to detect total body water (TBW) and its distribution in intracellular (ICW) and extracellular water (ECW). Echographic determination of the diameter of the inferior caval vein (VCD) provides information about the intravascular space (IVS). Nineteen PD-patients and 20 HD-patients in stable clinical condition were studied. In HD-patients a significant decrease in VCD, mean arterial pressure (MAP), TBW and ECW was noted due to ultrafiltration. Both ratios of VCD to ICW/ECW and of VCD to ECW/TBW decreased. No significant differences were found in these variables between PD-patients and HD-patients before HD. In both patient groups the measured variables pointed towards overhydration and the increased ratios both of VCD to ICW/ECW and VCD to ECW/TBW towards the storage of surplus of fluid in the intravascular space. It can be concluded that both PD-patients and HD-patients before HD have a surplus of fluid in the extracellular compartment, predominantly stored in the intravascular space.

Diameter of inferior caval vein and impedance analysis for assessment of hydration status in peritoneal dialysis.

In 19 stable peritoneal dialysis (PD) patients, hydration status was evaluated by measurement of vena cava diameter (VCD) and bioelectrical impedance analysis (BIA) variables: intracellular water (ICW), extracellular water (ECW), and total body water (TBW). We investigated whether BIA can replace VCD. VCD did not correlate with TBW but correlated moderately with ECW/TBW (r = 0.42; 0.025 < p < 0.05) and ICW/ECW (r = -0.47; p < 0.025). Patients with underhydration (n = 4; VCD <8 mm/m2) revealed limits for BIA variables as ICW/ECW (>1.50) and ECW/TBW (<0.40). The same held true for overhydration (n = 5; VCD >11.5 mm/m2): ICW/ECW (<1.50) and ECW/TBW (>0.40). Although the positive predictive value of ICW/ECW and ECW/TBW for both under- and overhydration was only 50% and 54%, respectively, there were no false negative values. Although BIA cannot replace VCD in PD patients, the reverse holds true as well. Combining BIA and VCD may lead to a better estimation of hydration status because both techniques provide complementary information.

The impact of equations on calculation of lean body mass by bioelectrical impedance analysis in RDT patients.

Several equations are available to derive lean body mass (LBM) from bioelectrical impedance analysis (BIA). The purpose of this study was to investigate in dialysis patients the impact of the equation used on the outcome of LBM assessment. To avoid dyshydration as a confounder, vena cava diameter measurement was used to assess normohydration in the 21 patients studied. Five equations were compared. In a previously published study to assess total body water using antipyrine as a gold standard, Deurenberg's formula was advocated to be used in the estimation of LBM by BIA. Therefore, this formula was used as a basis for comparison with the other four equations. One equation gave results comparable to those obtained by Deurenberg's formula. Despite high correlations and agreement according to Bland and Altman analysis, the other three equations showed a significant difference with Deurenberg-derived LBM. Thus, the equation used has a major impact on the outcome of LBM estimations.

Diameter of inferior caval vein (VCD) and bioelectrical impedance analysis (BIA) for the analysis of hydration status in patients on hemodialysis.

BACKGROUND: Vena cava diameter (VCD) measurement is an accepted method to evaluate hydration status in patients on hemodialysis. Bioelectrical impedance analysis (BIA) is a less laborious method to assess hydration variables and more suitable for routine patient care. However, BIA has not yet been validated in dialysis patients. We investigated whether BIA can replace VCD in patients on hemodialysis. METHODS: In 20 stable hemodialysis patients [age (+/-SD): 47+/-17 yrs, dialysis duration (+/-SD): 76+/-59 months] hydration status was evaluated by VCD. Impedance variables such as resistance, reactance and phase angle were provided by BIA. They were used to calculate intracellular water (ICW), extracellular water (ECW) and total body water (TBW). RESULTS: VCD did not correlate with TBW-BIA, but correlated with ECW/TBW (r = 0.46; p<0.025), ECW/m2 (r = 0.42; p<0.005) and ICW/ECW (r = -0.49; p<0.005). Hemodialysis decreased TBW with 2.7+/-1.91. The difference in ECW before and after dialysis (8.9+/-1.3 and 7.4+/-1.41, respectively) was significant (p = 0.001). The same did not hold true for ICW (13.3+/-1.4 and 13.1+/-1.41). Major underhydration (n = 9; VCD <6.5 mm/m2) revealed sharp limits for ICW/ECW (>1.80) and ECW/TBW (<0.35), whereas these BIA-variables were significantly (p<0.005) different from those in minor underhydration (n = 8; 6.6 < VCD <8.0 mm/m2), normohydration (n = 15; 8 11.5 mm/m2). CONCLUSION: BIA can replace VCD only in major underhydration (VCD < 6.5 mm/m2). Fluid loss during hemodialysis is caused by a decrease of ECW, compatible with the postulation that excess fluid volume is carried by the extracellular compartment.

Four-site skinfold anthropometry (FSA) versus body impedance analysis (BIA) in assessing nutritional status of patients on maintenance hemodialysis: which method is to be preferred in routine patient care?

BACKGROUND: Both four-site skinfold anthropometry (FSA) and bioelectrical impedance analysis (BIA) claim to be useful in routine clinical practice of maintenance dialysis as easy methods to assess nutritional status. The purpose of this study was to investigate which of these two methods is to be preferred. METHODS: Both before and after dialysis nutritional and hydration status were evaluated by BIA in 20 stable hemodialysis patients. Variables of nutritional status as lean body mass (LBM) and body fat (BF) were assessed by four-site skinfold anthropometry (LBM-FSA and BF-FSA) and BIA (LBM-BIA and BF-BIA). Variables of hydration status were total body water (TBW), its distribution into intracellular and extracellular compartments (ICW and ECW, respectively) and ICW/ECW. RESULTS: Weight loss during dialysis correlated with a change of LBM-FSA (r = 0.75, p <0.005) and also with that of LBM-BIA (r = 0.69, p < 0.005). To promote reliability of follow-up measurements in intervention studies it is warranted to evaluate nutritional status in an unchanged hydration status. The highly significant correlation (r = 0.93, p < 0.005) between the two techniques and the comparability between means and SD indicate that both techniques were almost equivalent to each other, although, compared to LBM-BIA, LBM-FSA was less affected by changes in fluid status. The sam held true for BF-BIA and BF-FSA. BF-FSA correlated significantly with BF-BIA (r = 0.65, p <0.005), whereas no difference of mean +/- SD was found between BF-FSA and BF-BIA. CONCLUSION: FSA and BIA are almost comparable techniques to assess both LBM and BF, although FSA is less affected by changes in fluid status. However, assessing LBM in normohydration is mandatory. Compared with FSA, BIA is able to establish hydration status and lacks depency on operator interpretation. Therefore, in routine patient care the BIA technique is the one to be preferred.

Detection of hydration status by total body bioelectrical impedance analysis (BIA) in patients on hemodialysis.

The purpose of the present study was to investigate whether total body bioelectrical impedance analysis (BIA) could be appropriate to assess normohydration (i.e. dry weight) in hemodialysis patients. This study is warranted, because the simultaneous assessment of both hydration and nutritional status by BIA requires the presence of a situation of normohydration in order to guarantee valid conclusions about the nutritional analysis. Segmental bioelectrical impedance was performed to classify patients according to their hydration status. BIA measurements revealed significant differences in TBW, ECW and ICW/ECW between three hydration subgroups (under-, normo-, and overhydration), whereas ICW was similar. Therefore, TBW, ECW and ICW/ECW appear appropriate variables to assess hydration status in patients on hemodialysis. Hemodialysis diminished ECW significantly, whereas ICW did not change, suggesting that a decrease of ECW explains the fluid loss during hemodialysis.