Journal Club: Is Longer Dialysis Treatment Time Associated with Better Outcomes?

Before we delve into the paper I plan to discuss lets get one key issue out of the way, namely, this is not a randomized controlled trial (RCT). Nevertheless, this is a terrific study addressing an important and timely issue.

In this paper in NDT, Tentori et al from DOPPS [based at Arbor Research, Michigan, USA] tested the hypothesis of whether longer treatment time (TT) is associated with improved outcomes – both intermediate outcomes, such as anemia parameters, hospitalization rates, phospohorus control, and more harder endpoints such as cardiovascular events and mortality. In addition, the authors also presented interesting data on regional differences in dialysis practice with respect to TT.

For me, the bottom-line is that this study provides further evidence to support using longer treatment times in managing dialysis patients. The short TTs in the US (only 12% had a TT >250 min in 2005–08) ought to be a wake-up call.

For some time, in my clinical practice, I have been pushing patients to accept longer treatment time. This analysis doesn't prove that longer TT's definitively make a difference - for that we need an RCT.

The sample comprised of

• N=37 414 patients on in-center HD three times per week with prescribed TT from 120 to 420 min in 930 facilities in 12 countries participating in the DOPPS (1996–2008)
• The cohort: The Dialysis Outcomes and Practice Patterns Study (DOPPS) prospective cohort study of in-center HD patients.

The key results

• Facility mean TT ranged from 214 min in the USA to 256 min in Australia–New Zealand.
• Among US DOPPS participants in 2005–08, only 12% had a TT >250 min, while 23% were dialyzed for <200 min.
• Mortality risk was lower for patients with longer TT {hazard ratio for every 30 min: all-cause mortality: 0.94 [95% 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)}.
• The strong association between longer TT and lower risk of sudden death remained after adjusting for patient comorbidities (like diabetes and atrial fibrillation) that are risk factors for sudden death
• 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. 

Strengths of the study

• Large sample size and the established DOPPS infrastructure and representative sampling approach across 12 countries.
• The use of time varying models that adjusted for both patient characteristics and DOPPS country and study phase and accounted for facility clustering.
• Use of an instrumental variable approach - with the dialysis facility as the instrument - in order to address patient-level unmeasured confounders which might impact the relationship between TT and outcomes. 

Weaknesses of the study

• Observational design. The authors cannot completely attenuate the feffects of confounding, especially residual from unmeasured variables. An RCT would have been ideal.
• There was an increase in TT over time in both the study (from 208 ± 32 to 221 ± 31 min) and that publication (from 201 ± 61 to 213 ± 59 min) – the authors argue the change was relatively small  - but it may have had an impact on clinical outcomes.