Longer dialysis session length is associated with better intermediate outcomes and survival among patients on in-center three times per week hemodialysis: results from the Dialysis Outcomes and Practice Patterns Study (DOPPS)

Abstract

Background: Longer dialysis session length (treatment time, TT) has been associated with better survival among hemodialysis (HD) patients. The impact of TT on clinical markers that may contribute to this survival advantage is not well known.

Methods: Using data from the international Dialysis Outcomes and Practice Patterns Study, we assessed the association of TT with clinical outcomes using both standard regression analyses and instrumental variable approaches. The study included 37,414 patients on in-center HD three times per week with prescribed TT from 120 to 420 min.

Results: Facility mean TT ranged from 214 min in the USA to 256 min in Australia-New Zealand. Accounting for country effects, mortality risk was lower for patients with longer TT {hazard ratio for every 30 min: all-cause mortality: 0.94 [95% confidence interval (CI): 0.92-0.97], cardiovascular mortality: 0.95 (95% CI: 0.91-0.98) and sudden death: 0.93 (95% CI: 0.88-0.98)}. Patients with longer TT had lower pre- and post-dialysis systolic blood pressure, greater intradialytic weight loss, higher hemoglobin (for the same erythropoietin dose), serum albumin and potassium and lower serum phosphorus and white blood cell counts. Similar associations were found using the instrumental variable approach, although the positive associations of TT with weight loss and potassium were lost.

Conclusions: Favorable levels of a variety of clinical markers may contribute to the better survival of patients receiving longer TT. These findings support longer TT prescription in the setting of in-center, three times per week HD.

Fig. 1.

Distribution of facility mean prescribed TT by DOPPS country and by phase. The box shows the 25th–75th and the whiskers the 5th–95th percentile ranges. *P < 0.05 for increase over time. DOPPS Phase 1 (1996–2001), Phase 2 (2002–04) and Phase 3 (2005–08). ANZ, Australia and New Zealand; BE, Belgium; CA, Canada; FR, France; GE, Germany; IT, Italy; JP, Japan; SP, Spain; SW, Sweden; UK, United Kingdom; USA, United States of America.

Fig. 2.

Distribution of patient-level prescribed TT categories by DOPPS country. DOPPS Phase 1 (1996–2001), Phase 2 (2002–04) and Phase 3 (2005–08). ANZ, Australia and New Zealand; BE, Belgium; CA, Canada; FR, France; GE, Germany; IT, Italy; JP, Japan; SP, Spain; SW, Sweden; UK, United Kingdom; USA, United States of America.

Fig. 3.

Association between prescribed TT (per 30 min longer) and risks of mortality and hospitalization. Adjusted model: adjusted for age, sex, race, time on dialysis, BMI, 13 summary comorbid conditions, residual kidney function, prescribed blood flow rate and catheter use, stratified by country and phase of study and accounted for facility clustering. CHF, congestive heart failure.

Fig. 4.

Association between prescribed TT and mortality by region. Interaction between TT and region (P < 0.0001). Longer TT was associated with lower mortality in Eur/ANZ [HR = 0.94 (95% CI: 0.91–0.97) per 30 min TT, P = 0.0002] and Japan [HR = 0.75 (95% CI: 0.69–0.81), P < 0.0001] but not in North America [HR = 0.98 (95% CI: 0.95–1.02), P = 0.28]. Model was adjusted for age, sex, race, time on dialysis, BMI, 13 summary comorbid conditions, residual kidney function, prescribed blood flow rate and catheter use, stratified by study phase and accounted for facility clustering. The chosen reference category was for North American patients with prescribed TT at 240 min.

Fig. 5.

Association between 30 min longer prescribed TT and achievement of clinical targets. Clinical targets are based on the Kidney Disease Outcomes Quality Initiative clinical practice guidelines for cardiovascular disease in dialysis patients [24], bone metabolism and disease in chronic kidney disease [25] and anemia [26]. Model adjusted for age, sex, race, time on dialysis, BMI, 13 summary comorbid conditions, residual kidney function, prescribed blood flow rate, catheter use, country and study phase and accounted for facility clustering; *model also adjusted for dialyzate K.