This month's eJournal club concerns a paper published by a fellow from our institution that attempts to get to the bottom of an interesting question: in patients with a high interdialytic weight gain (IDWG), is the dialysis session length (DSL) or the total volume gained more important? Both of these have been associated with increased mortality and both lead to an increased ultrafiltration rate (UFR). However, because they are interrelated, it is difficult to say which is more relevant.
For this study, the authors looked at more than 14,000 patients attending dialysis in the US. They excluded patients at extremes of session lengths and those who did not gain any weight between sessions. Patients with a URR less than 65% were also excluded to rule out any effects of underdialysis. The mean IDWG and DSL over 30 days were chosen as the exposures of interest. Interestingly there was high correlation between the 30-day IDWG and DSL and the 60 and 90-day means. The outcome was death from any cause. For the purposes of the analysis, the participants were divided into 2 groups for each exposure - less than or greater than 3kg IDWG and less than or greater than 240 minutes for DSL. A matched case-control study design was used.
Not surprisingly, the patients with higher IDWG tended to be younger, male, AA, had higher blood pressure and a higher prevalence of diabetes and CHF. Patients with lower DSL were more likely to be female, older and were less likely to have diabetes, CHF and CAD.
For the DSL analysis, lower DSL was associated with a HR of 1.32 (1.03-1.69) for mortality after full adjustment. For the IDWG analysis, increased IDWG was associated with a HR of 1.29 (1.01-1.69) for mortality. Thus both DSL and IDWG were independently associated with mortality.
What does this study mean for clinicians. It suggests that targeting both of these interventions could be useful. However it should be pointed out that this is an observational study and that they could not show that changing any of these exposures changed risk. Also, the because of the study design, the authors can only state conclusively that both are associated with mortality and not which one is more important. These conclusions may seem obvious but it is important to have good evidence to present to patients who may be frustrated with our requests to increase times and reduce fluid intake.
Head over the eJournal Club to continue the discussion of this paper.