Plasma Refill as a Marker of Ultrafiltration Intolerance During Inpatient Hemodialysis

Background: Fluid removal with hemodialysis (HD) is an essential treatment for fluid overload but can contribute to hemodynamic instability, particularly during acute illness and multi-organ dysfunction, when even modest rates of fluid removal can result in hypotension (ultrafiltration intolerance). We quantified plasma refill rate (PRR) in hospitalized patients receiving HD to examine whether PRR could be a useful metric of ultrafiltration intolerance. Methods: This is an observational study of patients receiving HD during acute illness at an academic hospital from March 2022-April 2025. HD treatment data were recorded prospectively and other clinical data were abstracted from the electronic medical record. PRR was calculated as the ratio of change in plasma volume (derived from changes in hematocrit measured on CritLine-IV®) to ultrafiltration volume. After discounting the effects of saline priming in the first 10min of HD, PRR was defined at 20, 30, and 60 minutes. Three definitions of intradialytic hypotension (IDH) were used based on systolic blood pressure (SBP) or mean arterial blood pressure (MAP): 1) SBP<90 mmHg, 2) if pre-HD SBP<100mmHg, then IDH was defined as either ΔSBP≥20mmHg or ΔMAP≥10mmHg, and (3) any ΔSBP associated with symptoms or intervention. Cox proportional hazard regression with a shared frailty model was used to examine the relationship between PRR and risk of intradialytic hypotension. Results: Among 204 patients (68.6% with end-stage kidney disease and 31.3% with acute kidney failure) we analyzed data from 292 HD sessions. IDH occurred in 14.5%, 12.2%, and 24.7% based on the three definitions, respectively. Low PRR<0.3 was associated with increased risk of IDH [HR 2.56 (95% CI 1.42, 4.60)]. Stratifying by prescribed ultrafiltration goal, the association of low PRR and IDH was attenuated in patients who previously tolerated more than 2L fluid removal and enhanced in patients with acute kidney failure, history of intolerance to modest ultrafiltration volume (< 2L per session, the median prescribed goal), and midodrine-dependence. Results were similar across different definitions of IDH and times of PRR assessment. Conclusion: PRR is a promising marker for hemodynamic stability during HD performed during acute illness and may be a particularly useful adjuvant metric in patients with evidence of ultrafiltration intolerance. Funding: NIDDK Support