Ultrafiltration Rate Levels in Hemodialysis Patients Associated with Weight-Specific Mortality Risks.

BACKGROUND: We hypothesized that the association of ultrafiltration rate with mortality in hemodialysis patients was differentially affected by weight and sex, and sought to derive a sex and weight indexed ultrafiltration rate measure that captures the differential effects of these parameters on the association of ultrafiltration rate with mortality.

METHODS: Data were analyzed from the U.S. Fresenius Kidney Care (FKC) database for 1 year following patient entry into a FKC dialysis unit (baseline) and over 2 years of follow-up for patients receiving thrice weekly in-center hemodialysis. To investigate the joint effect of baseline-year ultrafiltration rate and postdialysis weight on survival, we fit Cox proportional hazards models using bivariate tensor product spline functions, and constructed contour plots of weight-specific mortality hazard ratios over the entire range of ultrafiltration rate values and postdialysis weights (W).

RESULTS: In the studied 396,358 patients, average ultrafiltration rate in ml/h was related to postdialysis weight (W) in kg: 3W+330. ultrafiltration rates associated with 20% or 40% increases in weight-specific mortality risk were 3W+500 and 3W+630 ml/h, respectively, and were 70 ml/h higher in men than in women. Eighteen and 8 percent of patients exceeded ultrafiltration rates associated with a 20% or 40% higher mortality risk. Low ultrafiltration rates were associated with subsequent weight loss. ultrafiltration rates associated with a given mortality risk were lower in high-body-weight elderly patients, and higher in patients on dialysis for more than 3 years.

CONCLUSIONS: Ultrafiltration rates (ultrafiltration rates) associated with various levels of higher mortality risk depend on body weight, but not in a 1:1 ratio, and are different in men vs. women, in high-body weight elderly, and in high-vintage patients.