#4261 RELATIONSHIP BETWEEN FLUID OVERLOAD AND AVERAGE PLASMA REFILL RATE IN HEMODIALYSIS PATIENTS

Abstract

Abstract Background and Aims Attaining the optimal balance between achieving adequate volume removal while preserving organ perfusion remains challenging in patients on maintenance hemodialysis (HD). Quantification of fluid status using bioimpedance spectroscopy (BIS) has become routine in many countries. Inadequate vascular space refill from the interstitial tissue (plasma refill rate, PRR) is the main contributing factor of hemodynamic instability during HD. We aimed to explore the association between fluid overload (FO) and plasma refill rate (PRR) in chronic HD patients. Method Pre-HD FO [l] was assessed once per subject by BIS (Body Composition Monitor; Fresenius Medical Care) in four urban HD dialysis clinics in the U.S. For each treatment within 30 days before and after the BIS measurement, we calculated the respective pre-HD FO by assuming that differences in pre-HD body weight were equivalent to differences in FO. We then used intradialytic hematocrit (measured with the Crit-Line® Monitor, Fresenius Medical Care) and ultrafiltration data to quantify the average PRR, normalized by body weight (Wang et al. Kidney360, 2023): To calculate the starting blood volume (BV), we first calculated the ending BV using the Nadler equation, followed by back-calculating the starting BV based on the cumulative change in relative BV. Plasma refill volume was calculated as the sum of the changes in blood volume and ultrafiltration volume; plasma refill volume was then divided by treatment time and estimated clinical dry weight to calculate the PRR [ml/kg/hr]. Results We analyzed 746 HD sessions from 79 patients (age 61 ± 15 years; 52 (66%) males; 41 (52%) black and 33 (42%) white). Across all HD sessions, PRR was positively associated with FO [slope estimate 0.92 (95% confidence interval 0.83 to 1.02) ml/kg/hr per 1 l of FO, P value < 0.0001] (Figure 1). This was also the case in subgroup analyses of fluid depleted (r = 0.94, P<0.001), normohydrated (r = 1.03, P<0.0001), and fluid overloaded subjects (r = 0.83, P<0.0001). Conclusion Across the entire fluid status spectrum, from fluid depletion to fluid overload, higher FO was associated with higher PRR on average (overall, an increase of 0.92 ml/kg/hr in PRR for each additional liter of FO). While patients with greater FO would be expected to better tolerate higher ultrafiltration rates, there is large inter-individual variability in PRR. Further investigation of the utility of PRR throughout HD may offer novel insights into fluid management and intradialytic symptom mitigation.