Associations of Posthemodialysis Weights above and below Target Weight with All-Cause and Cardiovascular Mortality

Abstract

Background and objectives: Fluid removal via ultrafiltration is a primary function of hemodialysis, and inadequate volume control is associated with significant morbidity and mortality among chronic dialysis patients. Treatment-to-treatment fluid removal goals are typically calculated on the basis of interdialytic weight gain and prescribed target weight. The clinical effect of frequent missed target weights is unclear. This study was designed to evaluate the associations of postdialysis weights above and below the prescribed target weight (separately) and outcomes.

Design, setting, participants, & measurements: Data were taken from a national cohort of 10,785 prevalent, thrice-weekly, in-center hemodialysis patients dialyzing from 2005 to 2008 (median time at risk, 2.1 [25th percentile, 75th percentile] years) at a single dialysis organization. Patients were characterized as having an above target weight miss if their postdialysis weight was >2 kg above target weight in at least 30% of baseline treatments (14.6% of cohort), or they were characterized as control otherwise. Below target weight miss characterization was analogous for patients with postdialysis weight >2 kg below target weight (6.6% of cohort). Coprimary endpoints were all-cause and cardiovascular mortality.

Results: Above target weight miss in at least 30% of treatments (versus not) was associated with greater all-cause mortality (adjusted hazard ratio, 1.28; 95% confidence interval, 1.15 to 1.43); and below target weight miss in at least 30% of treatments (versus not) was associated with greater all-cause mortality (adjusted hazard ratio, 1.22; 95% confidence interval, 1.05 to 1.40). Both above and below target weight misses were also significantly associated with greater cardiovascular mortality. Secondary analyses demonstrated dose-response relationships between target weight misses and mortality. Results from sensitivity analyses considering the difference in postdialysis and target weights as a proportion of body weight were analogous to the primary results.

Conclusions: Postdialysis weights >2 kg above and below target weight are associated with higher all-cause and cardiovascular mortality. Consistent target weight achievement is a viable target for improving fluid management.

Keywords: cardiovascular; chronic hemodialysis; clinical epidemiology.

Figure 1.

Higher frequency of target weight misses (above and below) was incrementally associated with greater mortality. Adjusted associations between baseline target weight misses (above and below) and all-cause (Panel 1) and cardiovascular (Panel 2) mortality. Multivariable models contained exposure terms for both above and below weight and were adjusted for age, sex, race (black or nonblack), coronary artery disease, heart failure, diabetes, vascular access type (fistula, graft, or catheter), albumin (≤2.9, 3–3.9, and ≥4.0 g/dl), phosphorus (milligrams per deciliter), hemoglobin (grams per deciliter), equilibrated Kt/V, dialytic vintage (≤1.0, 1.1–1.9, 2.0–3.9, and ≥4.0 years), prescribed treatment time (minutes), interdialytic weight gain (kilograms), postdialysis weight (≤62.7, 62.8–74.0, 74.1–88.9, and ≥89.0 kg), predialysis systolic blood pressure (≤130, 131–150, and ≥151 mmHg), and missed dialysis treatments (0, 1, 2, and ≥3). 95% CI, 95% confidence interval; HR, hazard ratio; ref., reference population.

Figure 2.

Frequency of target weight miss by varying thresholds. Frequency of missed target weight was defined by the number of dialysis sessions with postdialysis weight above (and below) the prescribed target weight by differing thresholds divided by the total number of dialysis treatments in the baseline period.