Longer treatment time and slower ultrafiltration in hemodialysis: Associations with reduced mortality in the DOPPS

Longer treatment time (TT) and slower ultrafiltration rate (UFR) are considered advantageous for hemodialysis (HD) patients. The study included 22000 HD patients from seven countries in the Dialysis Outcomes and Practice Patterns Study (DOPPS). Logistic regression was used to study predictors of TT>240 min and UFR>10 ml/h/kg bodyweight. Cox regression was used for survival analyses. Statistical adjustments were made for patient demographics, comorbidities, dose of dialysis (Kt/V), and body size. Europe and Japan had significantly longer (P<0.0001) average TT than the US (232 and 244 min vs 211 in DOPPS I; 235 and 240 min vs 221 in DOPPS II). Kt/V increased concomitantly with TT in all three regions with the largest absolute difference observed in Japan. TT>240 min was independently associated with significantly lower relative risk (RR) of mortality (RR=0.81; P=0.0005). Every 30 min longer on HD was associated with a 7% lower RR of mortality (RR=0.93; P<0.0001). The RR reduction with longer TT was greatest in Japan. A synergistic interaction occurred between Kt/V and TT (P=0.007) toward mortality reduction. UFR410 ml/h/kg was associated with higher odds of intradialytic hypotension (odds ratio=1.30; P=0.045) and a higher risk of mortality (RR=1.09; P=0.02). Longer TT and higher Kt/V were independently as well as synergistically associated with lower mortality. Rapid UFR during HD was also associated with higher mortality risk. These results warrant a randomized clinical trial of longer dialysis sessions in thrice-weekly HD.