#4969 AN ADEQUATE HYDRATION MANAGEMENT IMPROVES THE EFFICIENCY OF INTRADIALYTIC PHOSPHATE REMOVAL
Authors: Kikuchi Hiroshi , Shimada Hisaki , Karasawa Ryo , Suzuki Masashi 
Published: June 2023

Abstract

Background and Aims
The excess of phosphate (P) is one of the major risk factors for death in patients undergoing hemodialysis (HD). Improving P removal efficiency should ameliorate their prognosis. We previously reported, increased urea nitrogen (UN) removal efficiency results in increased the removal efficiency of P from extracellular fluid (ECF), but did not improve that from intracellular fluid (ICF) (NDT, Vol 35, Sup3, P1401, 2020). We also reported that P removal from ICF accounted for in average about 44% of total intradialytic P removal. For improving total P removal efficiency, removal efficiency of P from ICF should be increased. As P is one of the major osmotic agents in ICF, water outflow from ICF will accompany P outflow. We explored correlation between intracellular P removal and intracellular water (ICW) reduction. And we also sought for the strategy which efficiently derive water from ICF in HD patients in order to increase intracellular P removal.

Method
Eighty-six patients undergoing 4-hour HD were enrolled this study. ICW, extracellular water (ECW) volume and body fat mass (BFM) in each patient were measured with biochemical impedance analysis method before and after HD session. Total body water (TBW) was calculated by ICW + ECW. The amount of intradialytic P removal from ICF and from ECF in each patient was calculated as previously reported (NDT, Vol 35, Sup3, P1401, 2020). The correlation between the amount of intradialytic P removal from ICF and the amount of ICW reduction was investigated. All patients were divided into three groups according to the amount of ICW reduction as high reduction (HR) group, middle reduction (MR) group and low reduction (LR) group. The amount of P removal from ICF was compared between these groups. ICW volume change (ΔICW%) was calculated as (preICW – postICW)/preICW in each patient. Where preICW = ICW volume at the starting of HD, postICW = ICW volume at the end of HD. Circulating plasma volume change (ΔCPV%) was calculated as (postTP – preTP)/postTP in each patient. Where postTP = serum total protein concentration (TP) at the end of HD, preTP = TP at the end of HD. Lean body mass (LBM) was calculated as BW – BFM. Body weight (BW) change (ΔBW%), LBM change (ΔLBM%) and TBW volume change (ΔTBW%) were calculated in the same way as ΔICW%. To seek factors that effectively reduce ICW, the correlation with ΔICW% in ECW/TBW ratio, ΔCPV%, ΔCPV%/ΔBW% ratio, ΔCPV%/ΔLBM% ratio and ΔCPV%/ΔTBW% ratio was examined.

Results
The amount of intradialytic P removal from ICF positively correlated to the amount of ICW volume reduction (R = 0.279, y = 66.3x+285, p = 0.0076). It indicates an average of 66.3mg of P was removed from ICF per 1L of ICW reduction. In HR group, the amount of P removal from ICF was significantly larger than that in LR group (315.6±117.8mg vs 383.7±121.7mg, p = 0.019). ΔICW% negatively correlated to ECW/TBW ratio (R = 0.481, p = 0.000057). High ECW/TBW ratio indicates excess of ECW, which suggests having edema. ΔICW% positively correlated to ΔCPV% (R = 0.511, p = 0.0000051). Low ΔCPV% suggests insufficient of ultrafiltration. ΔICW% negatively correlated to ΔCPV%/ΔTBW% ratio (R = 0.421, p = 0.00011). High ΔCPV%/ΔTBW% ratio indicates insufficient plasma refilling for ultrafiltration rate, which suggests overrate of ultrafiltration. But ΔICW% did not correlate to ΔCPV%/ΔBW% ratio (R = 0.184, p = 0.10) nor ΔCPV%/ΔLBM% ratio (R = 0.176, p = 0.12).

Conclusion
The amount of intradialytic P removal from ICF correlated to the amount of ICW reduction. For efficient reduction of ICW, low ECW/TBW ratio, high ΔCPV% and low ΔCPV%/ΔTBW% ratio were required. It was suggested that efficient P removal was achieved when non-edematous patients get ultrafiltration of appropriate rate and dose.