2005/1 EDTNA/ERCA Journal Club Discussion Summary 

Discussion of "Interdialytic weight gain as a marker of blood pressure, nutrition, and survival in hemodialysis patients" by Juan López-Gómez et al (Kidney International Supplement, 2005)

Compiled by EJ Lindley1 based on contributions from A Stragier2, JY De Vos3, K Lahuis4, S Shaldon5, D Green6, P McLaren7, M Pegoraro8, W Küntzle9, JE Tattersall1 and information requested from J Lopez-Gomez10.

1Department of Renal Medicine, Leeds Teaching Hospitals NHS Trust, UK; 2Bierbeek, Belgium; 3Werken Glorieux, Ronse, Belgium; 4Dianet Amsterdam Medical Centre, The Netherlands; 5Monaco; 6 Department. of Nutrition and Dietetics, Hope Hospital, Salford, UK; 7Lister Hospital, UK; 8 Centro Dialisi, Corsico, Italy; 9Patienten Heimversorgung, Ludwigsburg, Germany; 10Service of Nephrology, Hospital Gregorio Marañón, Madrid, Spain

The paper selected for discussion by the EDTNA/ERCA Journal Club in February 2005 was “Interdialytic weight gain as a marker of blood pressure, nutrition, and survival in hemodialysis patients.” [1]. The authors work in the Service of Nephrology, Hospital Gregorio Marañón , Madrid, Spain and the corresponding author, Dr Juan Lopez-Gomez, kindly agreed to take part in the discussion and respond to any queries raised.

Synopsis of the discussion paper

The discussion paper can be downloaded in full from the EDTNA/ERCA website (see ref. 1). The authors of this paper wanted to assess the long-term prognostic effect of interdialytic weight gain (IDWG) and to look at the relationships between IDWG and nutritional status and blood pressure.

The study involved observing a group of 134 haemodialysis patients (70 males, 64 females, aged 18 to 81) for five years. At the start of the study, the authors collected a range of nutritional parameters, and the average IDWG and blood pressure over 12 consecutive HD sessions. They found that the mean IDWG for the group was 3.5±1.1% of dry weight (range 1.5 to 8.0%). Lower IDWG% was associated with increased age and serum bicarbonate, higher IDWG% was associated with increased nPCR, body mass index and predialysis urea, creatinine, phosphate, albumin and prealbumin. Higher IDWG% was also associated with higher pre-dialysis systolic and diastolic blood pressure. There was no relationship between IDWG% and gender.

To assess the effect of IDWG on survival, the patients were divided into three cohorts with IDWG% <2.9%, 2.9 to 3.9% and >3.9%. After five years, only 38% of the cohort with the lowest IDWG were still alive, compared to 52% of the middle cohort and 63% of the cohort with the highest IDWG.

The authors concluded that the greater the IDWG%, the better the long-term prognosis as the beneficial effects on nutritional status outweigh the negative effects of increased blood pressure. They suggest that restrictive advice that could give rise to a negative effect on nutrition should be avoided.

Measurement of nPCR

Andre Stragier commented that, in agreement with the paper, he had found an excellent correlation between nPCR and IDWG (p < 0.001) when working at St Luc in Brussels. He also made a technical observation on the measurement of nPCR using the so called ‘3-point’ and ‘2-point’ method. The 3-point method (using, for example, pre and post-dialysis ureas for Monday and a pre-dialysis urea for Wednesday) gives an nPCR based on the urea generation rate for the interval between the two sessions. The 2-point method, which uses only pre and post-dialysis urea for one session, gives an nPCR based on an estimated urea generation rate that is assumed to be constant throughout the week.

Staff at St Luc had noticed that there was a significant difference between nPCR when assessed using the so called ‘3-point’ method for the first and second sessions of the week and ‘2-point’ method for the first session. Investigations showed that daily weight gain and nPCR calculated by the 3 point method were, respectively, 7 – 15 % and 5 – 6% lower (p < 0.05) over the long weekend interval compared to the 2-day intervals in the week. The lower IDWG over the weekend occurred whether or not the patients were expecting blood samples to be taken, so it appears that patients modify their dietary intake over the long weekend interval to avoid problems. As a result, the patients’ average nPCR is overestimated if calculated by the 3-points method at the beginning of the week [2].

Reversed epidemiology?

Jean-Yves De Vos agreed that in anuric patients on conventional (3 times weekly) HD, low IDWG% was likely to indicate underlying problems and that it could be expected that patients with low IDWG% would die earlier. But he felt that to aim for a high IDWG% in all patients would be inappropriate.

Kristel Lahuis also thought the conclusion sounded like reversed epidemiology and felt we should be aiming for both a lower IDWG and good nutritional intake. This is possible with good nutritional coaching which can have a lot of influence on compliance on diet (both fluid and protein/energy aspects). Kristel added that it is the job of a dietitian to be creative in finding foods that are salt and fluid restricted but also of nutritional value.

Another possible problem with the epidemiology was raised by Stanley Shaldon who noted that the mean ages of the low, medium and high IDWG% cohorts were 68, 63 and 51 years respectively. He pointed out that it is not surprising that 51 year olds live longer than 68 year olds and that there does not appear to be any statistical correction for age in the paper so the association maybe spurious.

Sodium or fluid restriction?

The rest of the discussion focussed on sodium. Prof Shaldon quoted from a letter Evert Dorhout Mees entitled ‘Thirst in Dialysis Patients’ [3] which he felt expressed his critique of the discussion paper perfectly. ‘That thirst is influenced by salt consumption is an every day experience and results from the fact that thirst serves osmoregulation.... Yet, this simple truth is being neglected by some dialysis doctors.... Trying to contain volume expansion resulting from salt by water restriction is not only cruel but also futile: thirst is one of the most powerful urges. Dialysis patients all over the world are tormented by instructions to limit fluid intake instead of limiting dietary salt.’

Prof Shaldon described an experiment in Seattle in the late 1990’s when patients were instructed to eat a low salt diet. Although no mention of fluid intake was made, IDWG fell by one kilogram [4], confirming the observation of Dorhout Mees.

One of the authors of this paper (Alison Rigby) described fluid restriction as ‘rather like asking a thirsty desert traveller to refrain from drinking water from a bubbling brook that he happens to come onto along the way. By re-directing this effort to help the patient restrict sodium intake, IDWG would be lower and control of blood pressure would be much improved.’ [5]

In an earlier contribution to the discussion, Jean-Yves De Vos asked the authors why sodium was not followed in the study. Dr Lopez-Gomez responded, agreeing that including dietary sodium intake in the paper would have been very interesting, but said that it is very difficult to assess in practice. However, in his unit, the nurses and physicians do constantly insist on the necessity to eat food with low salt content. Dr López-Gómez agreed with Prof Shaldon’s point that salt intake is the key factor in IDWG.

Reducing sodium intake

Diane Green commented that, in the UK, dietitians are aiming for an intake of less than 100mmols Na daily but are finding it very hard to achieve this without compromising nutritional status as patients are often encouraged to use ready made foods on dialysis days to ensure that they eat something. The amount of salt added by the manufacturers of this type of food is a major problem.

Prof Shaldon felt that a salt restricted diet and good nutrition are perfectly compatible as shown by the basic Mediterranean diet which is low in salt. He agreed with Diane that using processed foods leads to very high sodium intakes [6]. Habitual high salt eaters lose the salt sensitivity of their taste buds and need more salt to achieve the same taste sensation. Patient compliance with a low salt diet is difficult unless this sensitivity can be restored and this can only be done by continuous insistence on a low salt diet intake. As IDWG goes down, it is also important to reduce the sodium content of the dialysate until the patient no longer feels thirsty at the end of dialysis. This will take months and a very hard team input to achieve, but the results will be very rewarding. With no instructions on fluid intake and 5g salt intake per day, a 70kg anuric male on 3 x week dialysis should have an IDWG or 1.5kg provided the dialysate sodium is less than 140mmol/l.

Where a reduced salt intake can be maintained, Prof Shaldon explained, the blood pressure becomes low normal without drugs, heart size normalises, left ventricular hypertrophy is reduced and the haematocrit rises spontaneously. Tolerance to dialysis increases despite a low normal blood pressure, IDWG is reduced and a lower sodium dialysate (135-137 mmol/l) is well tolerated. In the few long-term studies available, survival is improved.

Paula McLaran explained that she teaches fluid management to nurses and finds they are often amazed by the evidence that suggests that restricting sodium can have a huge effect on reduction of IDWG, even with no fluid restriction. Paula’s unit recently undertook a study of the effect of dietary sodium intake on IDWG, sodium mass balance and blood pressure. Interdialytic food diaries showed that that most of the patients ate over the 5g/day salt recommended by the World Health Organisation. Higher salt intake was associated with higher IDWG in anuric patients, but not in patients who were still passing urine.

Paula made the point that we have been focussing on dialysis adequacy in terms of urea clearance (UKM and Kt/V), when we should be focussing just as hard on the implications of fluid overload for our dialysis patients. This concept is explored very elegantly by Prof Dorhout Mees in an editorial on dialysis adequacy that was suggested as a reference on salt restriction by Prof Shaldon [7].

Survey of advice given to patients

During the discussion, I sent a brief questionnaire to some of the active volunteers in EDTNA/ERCA to find out how staff in their centre usually advise patients who are gaining too much fluid between sessions, but who have a normal pre-dialysis sodium. The options were:

A. Advice on how to reduce their fluid intake and curb their thirst (e.g by sucking ice cubes), but NO advice on restricting salt intake.

B. Advice on both fluid and salt but with emphasis on monitoring fluid intake (ml/day).

C. Advice on both fluid and salt but with emphasis on monitoring salt intake (g or mol/day).

D. Advice on how to reduce their salt intake (e.g. explanation of salt content in processed foods), but NO advice on restricting fluid intake.

The replies from 15 volunteers in 8 countries are shown in figure 1. 75% of their centres focus on fluid restriction to manage weight gains. Nurses gave this advice in all the centres, dietitians also provided advice in 5 centres and doctors in 3.

Figure 1. Advice on control of interdialytic weight gains

Marisa Pegoraro commented that although the nurses in her unit normally used type B (sometimes C), advice, the counselling patients received from each other was often on ways to curb their thirst with no consideration of salt intake.

Some information on the availability of dietetic advice was provided by Jean-Yves De Vos. In Flanders, 50% of centres have a dialysis dietitian the other 50% do not (but can call for a general hospital dietitian if necessary). A survey of practice showed that in Flemish centres without a dialysis dietitian, 75% of dietary advice is given by nephrologists and 25% by nurses [8].

Jean-Yves also brought up the psychological aspect of providing advice on IDWG. He felt it might be very frustrating for a patient to be confronted over and over again because they are gaining more weight between sessions than the clinical staff would like to see, when they feel they are already doing their best to control their weight gains. These confrontations could be humiliating for patients, especially as there is no privacy in the dialysis rooms, so clinical staff should try to think every time how they would feel in the patient’s situation.

Waltraud Küntzle agreed that patients should not have to feel humiliated and that nurses needed to try to change patient education to suit the patient’s attitude and resources. The first, and most essential, step is to convince the patient to have the will and desire to change their nutrition. If the patient is willing to make a behavioural change in nutrition, then the nurses should give the best possible support. If it becomes clear that, despite understanding the advice given, the patient is not able or not willing to change their behaviour, the nurses have to accept this. If they don’t, the unnecessary, humiliating and frustrating ‘Dialogue des sourds’ (dialogue of the deaf) will continue, as patients will always obey their thirst more than their nurse.

Changing the focus of advice

A number of private communications suggested that nursing staff working in units giving type A advice (i.e. advice on restricting fluid intake and trying to curb thirst) were concerned that changing to advice on salt restriction would lead to an impossible workload. James Tattersall was kind enough to described his experience of working with nursing staff to gradually convert a dialysis unit from type A to type D advice. It is reassuring to see that very intensive salt education is required for relatively few patients.

In the early 1990’s, Dr Tattersall worked in a unit which performed relatively short dialysis so fluid and BP management was critical. They quickly confirmed Prof Shaldon’s observations that fluid restriction is useless and distresses the patient. On the other hand, salt restriction really helped to reduce fluid intake and was well tolerated by the patient once they got used to it. Salt intake on dialysis was limited by avoiding Na modelling and saline infusions.

In 1998, Dr Tattersall moved to a dialysis unit where patients received type A advice. Patients were given a fluid restriction and those who could not keep to it were labelled ‘non-compliant’. Most patients consumed salty snacks during dialysis and hypotension and cramps were treated by IV saline. There were the usual problems with fluid overload and hypertension. There is no ‘quick fix’ in this situation. It is hard to change behaviour, especially where food is concerned. Each patient is different and requires a different approach. Looking back, Dr Tattersall could describe the ‘conversion’ process in six steps.

Step 1 was to lift fluid restriction and give general advice on salt. This involved getting all the staff to agree that it was impossible or at least very unpleasant to restrict fluid. Patients were given general advice on salt but no salt limits were imposed. Salty snacks on dialysis were discouraged and IV saline infusions and wash-back was minimised. There was resistance at the start but at least the ‘non-compliant’ patients felt better understood and the nurses no longer felt under pressure to berate the patients. Weight gains did not increase when the fluid restriction was lifted. Blood pressure generally improved and it became easier to achieve target weight.

Step 2 was to gradually stop antihypertensive drugs apart from those which block the angiotensin system (see below). Most antihypertensive drugs prevent fluid removal on dialysis by antagonizing the vascular refilling and vasoconstriction which is required to maintain blood volume and pressure during ultrafiltration. After stopping these drugs, dialysis was generally better tolerated and blood pressures did not rise. These drugs do not work if the patient is overloaded.

Step 3 was to start aggressive fluid removal in the hypertensive patients (about 70% of the unit). The patients were warned to expect some symptoms at the end of dialysis and profiled UF was used (faster at the start of HD, slowing towards the end). After six months of ‘drying out’, 50% of the patients in the unit were still hypertensive.

Step 4 was to start the remaining hypertensive patients on an angiotensin receptor blocker or angiotensin converting enzyme inhibitor (if not already on it). These drugs drug reduce blood pressure, reduce the risk of cardiac disease, reduce cardiac and arterial hypertrophy and, in theory reduce thirst and increase vascular refilling. Hypertension on dialysis is partly caused by fluid overload, partly by angiotensin excess and partly by arterial and cardiac hypertrophy. The hypertrophy is a response to high blood pressure and angiotensin which takes many months to reverse. After about six months on this medication regime only 30% of the patients in the unit were still hypertensive.

Step 5 involved giving specific advice (depending on their diet) on how to cut salt intake by about 30-50% to hypertensive patients who had IDWG of less than 3% of dry weight and normal or high pre-dialysis sodium. In general this was fairly easy to achieve by measures like not adding salt to food, avoiding salty snacks etc. An exception was made to the ‘no fluid restriction’ rule for the one or two patients had low pre-dialysis serum sodium levels due to a drinking habit that was not driven by salt. The small group of hypertensive patients with IDWG below 3% were prescribed an additional blood pressure lowering drug.

Step 6 was used only for the 10% of patients were still hypertensive with IDWG >3% and normal or high blood sodium, despite specific advice on salt reduction. It involved progressively stricter limits on salt intake and, in some cases, a longer dialysis. Patients found that a strict salt limit was hard initially as they felt their food was tasteless, but those who could maintain the restriction got used to lower salt levels and found food tasted normal again. These patients also found that they no longer had excessive fluid weight gains and their blood pressure became normal. A few patients were unwilling or unable to restrict salt and remained hypertensive.

Dr Tattersall emphasised that the steps described above were not made as part of a deliberate strategy, they ‘evolved’ as he learned more about the way patients responded. But he hopeed the information on the effects of each step might be helpful to other units planning a similar change.

A description of treating hypertensive patients with a combination of lower salt intake and gradual reduction of dialysate sodium from 140 to 135 mmol/l is given in ref. 9.

Conclusion

Whilst no-one strongly disputed the observations made by the authors of the discussion paper, their conclusion that ‘the greater the IDWG%, the better the long term prognosis of the patients’ was felt to be misleading. The first reactions to the paper were that low IDWG did not cause patients to die sooner, but that patients who were more likely to die would have lower IDWG.

There was unanimous agreement that sodium restriction was the key to controlling IDWG. Although the authors did not report on sodium intake or pre-dialysis serum sodium, they stressed the importance of nutritional education to reduce salt consumption. Prof Shaldon gave a very compelling case for restricting salt intake, rather than fluid consumption (or IDWG), as patients who eat too much salt will have an uncontrollable urge to drink.

The survey of EDTNA-ERCA active volunteers showed a wide variation in practice, with many units focussing attention on control of fluid intake rather than salt. Dr Tattersall provided some practical information on changing the emphasis from fluid to salt restriction.

Prof Shaldon and Waltraud Küntzle provided ideal closing comments for this discussion:

· From Prof Shaldon: ‘The cost effectiveness of salt restriction is enormous and its virtually total neglect in 2005 represents a therapeutic tragedy.’ [10, 11]

· From Waltraud: ‘I am completely aware, that here in Germany we do NOT tell our patients enough about salt restriction and we do not focus enough in our training for nurses on this topic. The discussion has stimulated me to include and highlight this in our nutrition module.’

Take-home message from the discussion

‘Give your patients advice, education and encouragement on how (and why) to restrict their salt intake. Attempting to control a patient’s interdialytic weight gain by restricting fluid is cruel and ineffective.’

Acknowledgements

We are very grateful to Dr Saulo Klahr, editor of Kidney International, for giving us permission to circulate the paper freely to our members and to Dr Juan Lopez-Gomez for participating in the discussion.

We would also like to thank Christel Levebre of United Networks in Belgium for providing technical support for the Journal Club mailing system and Patricia Morrissey, Manuscript Editor at KI, for her invaluable help in negotiations with Blackwell Publishing.

And finally, thanks to the EDTNA-ERCA volunteers who responded to the questionnaire.

References

Lopez-Gomez JM, Villaverde M, Jofre R, Rodriguez-Benitez P, Perez-Garcia R. Interdialytic weight gain as a marker of blood pressure, nutrition, and survival in hemodialysis patients. Kidney Int Suppl. 2005 Jan;93:S63-8.
You can download this paper here.

Stragier A and Jadoul M. Daily weight gain and protein catabolic rate are lower over the long interdialytic interval. Clin Nephrol. 2003 Jul;60:22-7.

Dorhout Mees EJ. Thirst in Dialysis Patients. Kidney Int. 2005 Mar;67:1192.

Rigby-Mathews A, Scribner BH, Ahmad S. Control of interdialytic weight gain does not require fluid restriction in hemodialysis (HD) patients. J Am Soc Nephrol. 1999 10:267 (Abstract).

Rigby AJ, Schribner BH, Ahmad S. Sodium, Not Fluid, Controls Interdialytic Weight Gain. Nephrol. News & Issues 2000;14:21-2.
You can find this article at http://www.ikidney.com/iKidney/Community/Pro2Pro/Dietitians/SodiumNotFluidControlsInterdialyticWeightGain.htm.

MacGregor G. Salt: blood pressure, the kidney, and other harmful effects. Nephrol Dial Transplant 1998;13:2471-9
You can download this paper from the NDT website without charge here.

Dorhout Mees EJ. Adequacy of dialysis: An inadequately applied concept. Dialysis & Transplantation 2004; 11.

For more details please visit the ORPADT Flemish website at www.orpadt.be

Krautzig S, Janssen U, Koch KM, Granolleras C, Shaldon S. Dietary salt restriction and reduction of dialysate sodium to control hypertension in maintenance haemodialysis patients. Nephrol Dial Transplant. 1998 Mar;13(3):552-3.
You can download this paper from the NDT website without here.

Shaldon S. How can survival of the well-dialyzed patient be increased? Neptune’s poisoned chalice: A tragedy of modern Therapeutics. Semin Dial. 2000 Jan-Feb;13(1):11-12.

Shaldon S. Dietary salt restriction and drug-free treatment of hypertension in ESRD patients: a largely abandoned therapy. Nephrol Dial Transplant. 2002 Jul;17(7):1163-5.
You can download this paper from the NDT website without charge here.