eJournal Club – Session length and weight gain

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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.


  1. Great comment, thanks. I think that's the real value of Jenny's research.

  2. Recently, I switched to a new dialysis unit because of moving out of state. One of the first things the nurse stated to me in a very harsh tone was, I understand you refused a transplant. I explained, patiently, not so. I declined to choose a transplant because of two prior cancers, testicular in medical school and melanoma shortly after starting dialysis. Interestingly, the melanoma was found by my request for a dermatology screen as part of my transplant evaluation.

    Using the term "noncompliance" underlies the prevalent imbalance in the doctor-patient relationships in dialysis units. It ignores the physiology of myocardial ischemia inducing permanent damage to the heart of dialysis patients from excessive ultrafiltration rates even in incident dialysis patients who still have significant residual renal function. It further ignores the fact that it is physiologically impossible to remove large amounts of fluids with negatively impacting cardiovascular stability.

    Mr Hussein (?MD) correctly recognizes the only proven remedy of high IDWG, longer and more frequent dialysis. As a medical student and resident, I was terrorized by nephrology attendings on rounds with minute details of physiology. Nephrology is an exacting discipline. Yet as a dialysis patient, the simple relationship between 3rd space fluids and refilling the cardiovascular compartment is the rate limiting factor of ultraflitration largely ignored by the nephrology community to the serious detriment of the patients they are entrusted with their care.

    The medical facts are clear, longer and more frequent dialysis reduces LVH (FHN short daily study) and reduces morbidity and mortality (multiple observational studies and FHN short daily study trends) The social implications of how nephrologists view their patients likewise is quite clear when you step onto this side of the needle. Most patients who have undergone conventional in-center hemodialysis with short, rapid ultrafiltration suffer from permanent mycardial damage with significant LVH and CHF. Couple this with the very common practice of sodium profiles during rapid ultrafiltration and I truly must question the term "noncompliant" when in fact, it is simple long standing iatrogenic complications leading to high IDWG.

    Perhaps when the nephrology community acknowledges the true relationships between IDWG, high ultrafiltration rates, sodium modeling and myocardial ischemia/cardiac stunning/ cardiac hybernation, perhaps then, the iatrogenic nature of IDWG will strike a chord of introspective self examination of the prohibition of the Hippocratic Oath, first do no harm.

  3. Thanks Gearoid for bringing this here. Quite an interesting study. I am particularly intrigued by the design the authors implemented to get at a question that lingered for so long with no similar attempts to answer it.

    Unfortunately, we have little to provide the patient with high IDWG (inter-dialytic weight gains) but longer or more frequent dialysis. Extending dialysis times is even harder when the cause of fluids accumulation is non-compliance with dialysis. A few important approaches need not be forgotten:

    1. It is of utmost importance as nephrologists that we preserve residual renal function by avoiding nephrotoxics, controlling hypertension and using RAAS inhibitors. We need to maximize on the advantage of continuing to have some urine output in those who have any. High dose loop diuretics, by increasing urine volume, will reduce IDWGs, in addition of course to helping with hyperkalemia, a common problem in non-compliant patients.

    2. Telling our patients not to drink is not the best advice. Although this may help reduce habitual drinking, the main drive for thirst is hypernatremia. Asking them to reduce salt intake should take higher precedence. It is sometimes hard for patients to follow this advice because of social and financial issues limiting their food selection, but it is our role to educate them so they can make the right choices when they can. This article discusses different groups of patients for their drive to drink: http://www.ncbi.nlm.nih.gov/pubmed/19573006

    3. We have to be cautious not to contribute to patients IDWG. High dialysis Na contributes to the patient's sodium intake and thus stimulates thirst. Careful reductions in dialysate Na to match a patient's serum Na was shown to reduce IDWGs. I encourage all trainees to have a look at this study: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3660723/

    Besides patients understandable objection to having longer or more frequent sessions, there are huge financial implications to extending dialysis times. Investing in alternative measures may help a few to achieve better outcomes out of their limited times.

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