Nature of the filtration coefficients of the microvasculature in the vicinity of dry weight in hemodialysis patients - as a marker of the fluid status

Plasma refilling from the extravascular compartment during hemodialysis (HD) is a major compensatory mechanism to maintain the blood pressure. Plasma refilling rates are proportional to the filtration coefficients of the microvasculature (Lpst) and colloid-osmotic pressure gradients minus hydrostatic pressure gradients. A decreasing tendency of Lpst according to the volume reduction with ultrafiltration (UF) was reported. The aim of this study is to investigate the relation of Lpst with other markers of the fluid status and to clarify that Lpst can be utilized as a marker of the fluid status of HD patients. A total of 106 patients on maintenance HD were examined. Atrial natriuretic peptide (ANP), inferior vena cava diameter by ultrasound (IVCe/BSA), and excess fluid mass (ExF/DW) by bioimpedance spectroscopy were measured at the end of HD. Blood volume change (ΔBV/TUF/DW) and Lpst in the vicinity of dry weight were calculated by means of monitoring changes of hematocrit with CRIT-LINE™. Lpst correlated significantly with ANP, IVCe/BSA, ABV/TUF/DW, and ExF/DW (0.461, 0.408, -0.479 and 0.590, P<;0.01, respectively). ExF/DW and Lpst were significantly higher in hypertensive patients at the end of HD than in nonhypertensive (-0.56±2.07 vs. 0.83±2.41%, P<;0.01, 1.17±0.86 vs. 1.77±1.21ml/mmHg/min, P<;0.01, respectively). There were significant differences in Δ BV/TUF/DW, ExF/DW, and Lpst between patients who were prone to intradialytic hypotension (IDH) and those who were not (3.27 ±1.44 vs. 2.67±1.16, P<;0.05, -1.16±1.91 vs. 0.67± 2.35%, P<;0.01, 1.00±0.90 vs. 1.68±1.14 ml/mmHg/min, P<;0.02, respectively). ExF/DW, ultrafiltration rate (UFRlDW), and ANP were independently associated with Lpst on multiple linear regression analysis (R=0.703). Therefore, Lpst may not properly reflect the volume status of a patient. We concluded that there are sign- ficant associations of Lpst with other markers indicating the fluid status in HD patients. This result suggests the potential to utilize Lpst as a tool for assessing the fluid status and determining an adequate DW. Lpst may be independently affected by the fluid status in the vicinity of DW, UFR/DW, and plasma ANP level. Because UFR and ANP have a marked impact on Lpst, it may be better to adjust Lpst with these factors for its utilization as a marker of the fluid status of HD patients.