Gardiner, C

Keane, D

Lindley, E

Wright, M

Leeds Beckett Repository

69www.bjrm.co.ukElizabeth J LindleyPhD CSci SpecialistClinical Scientist inRenal Care1 and RenalTheme Lead2Claire GardinerBSc(Hons) SeniorSpecialist RenalDietitian3David Keane BSc(Hons)Research Fellow1Mark Wright MB ChBFRCP MD ConsultantNephrologist41 Departments of RenalMedicine and MedicalPhysics, Leeds TeachingHospitals NHS Trust2 National Institute forHealth Research Devices DignityHealthcare TechnologyCo-operative, SheffieldTeaching Hospitals NHSFoundation Trust,Sheffield3 Department of Nutritionand Dietetics, LeedsTeaching Hospitals NHSTrust4 Department of RenalMedicine, LeedsTeaching Hospitals NHS TrustAlthough you may sometimes put on ‘real’weight (that is, flesh weight) betweendialysis sessions, especially after a bout ofillness, interdialytic weight gain (IDWG) isusually due to the accumulation of fluid. Thisarticle is about managing interdialytic fluidgain (IDFG). As long as you do not gain orlose real weight, your IDWG in kilograms willbe the same as your IDFG in litres.Fluid gained between dialysis sessions is mostlyextracellular fluid, which is all the body fluid that isnot inside cells. Extracellular fluid contains glucoseand the salts of various metals. The most abundantmetal in extracellular fluid is sodium, which mainlycomes from sodium chloride (common salt) in yourdiet. The sodium in one litre of extracellular fluid isequivalent to about eight grams of salt.The kidneys normally help to control the volumeand the sodium level of the extracellular fluid byexcreting excess sodium and water in urine. If yourkidneys are unable to do this, your body can controlthe level of sodium in the extracellular fluid bymaking you thirsty.How does my body make me thirsty?There are two types of thirst: volumetric andosmometric. You experience volumetric thirst if your extracellular fluid volume is too low, which may happen after dialysis. The low fluid volumecauses a reduction in blood flow to the kidneys, which activates the renin-angiotensin system (RAS). The RAS generates hormones that raise your blood pressure to keep the kidneys working, as well as decreasing urine production and making you feel thirsty. You may have beenprescribed drugs that block the production of these hormones (such as ramipril or losartan) to help control your blood pressure.The kind of thirst you experience when the level of sodium in your extracellular fluid gets too high is osmometric thirst. There is a sensor in your brain called the osmostat. Just as the thermostat in a cooling system prevents overheating, your osmostat stops the sodium level in yourextracellular fluid getting too high. When yoursodium level goes above your set point, the osmostat will compel you to drink.Figure 1 shows the pre-dialysis sodium levels of375 haemodialysis patients measured over sixmonths. For each individual, the red dot is the average monthly sodium measurement, and the blue whiskers show how much their sodiumvaried during that time. For most patients thevariation was only a few mmol/l. The wide variationbetween patients is partly due to the difference intheir individual osmostat set points. A low pre-dialysissodium level is usually due to high fluid intake,although it can also be due to low salt intake orsodium loss in urine or via the gut (through a highoutput stoma or through diarrhoea). People withdiabetes tend to have lower sodium levels becausehigh blood sugar levels make you thirsty regardless of your salt intake. If you use PatientView, you can check your ownsodium levels from your monthly blood results. If not,the nursing staff or your dietitian will be able to showyou your sodium levels for the last few months.Do all dialysis patients gain fluid between sessions?Your IDFG will depend on your daily fluid intake, thetime between sessions and how much urine you pass.Some people need dialysis because their kidneyscannot adequately remove toxins from the body, butcan still remove enough fluid. For those people, thereshould be little or no increase in weight betweensessions, even if the dialysis machine removes onlythe minimum amount of fluid.Most people still produce some urine when they start dialysis. Although this residual kidneyBRITISH JOURNAL OF RENAL MEDICINE 2015; Vol 20 No 3 Patient informationWhat I tell my patientsabout interdialyticweight gainIn patients receiving haemodialysis, interdialytic weight gain (IDWG) is the weight increase between the end of one dialysis session and the start of the next. ElizabethLindley and colleagues describe how to manage this weight gainCopyright © Hayward Medical Communications 2015. All rights reserved. No unauthorised reproduction or distribution. For reprints or permissions, contact edit@hayward.co.uk70 www.bjrm.co.ukfunction can last for years, it normally decreases over time. As the kidneys lose their ability to produce urine, more fluid will accumulate betweensessions. People with little or no residual functionusually have to restrict their salt and fluid intake to control their IDFG. This is one reason why it isimportant to make sure that your kidneys keepworking for as long as possible, even after you have had to start dialysis.Residual kidney function decreases rapidly if you become dehydrated at the end of dialysis.Dehydration is not unusual, especially if you havegained flesh weight since your target weight was set,or if you have high blood pressureand your doctor is ensuring thatyou are not fluid overloaded.1 It isimportant to let the nursing staffknow if the amount of urine youare passing drops markedly,especially if this happens just after your target weight has been reduced or you think you have put on weight. What should my interdialytic fluid gain be?The current guidelines from the UK Renal Associationsuggest that the rate of fluid removal duringhaemodialysis is kept at less than 10 ml/kg/hour.2 Thiscorresponds to a maximum IDFG of approximately1% of target weight per hour of dialysis. For a personwho weighs 70 kg and dialyses for four hours, thisworks out at 2.8 litres. In our unit, an allowance of0.4 litres is made for drinks and the fluid used to washthe blood back from the dialyser, giving a maximum IDFG of 2.4 kg for a person who weighs 70 kg.In practice, you and the staff at your dialysis unitwill usually come up with a maximum IDFG based onthe amount of fluid you can remove during dialysis.This will depend on how long your sessions are andhow well you tolerate fluid removal.It is important to remember that the amount offluid you can remove without feeling unwell willdepend on the amount of excess fluid in your body. Itis usually much easier to remove fluid if you are veryoverloaded, and much harder if you are close tonormal hydration. Other factors that affect how wellyou tolerate fluid removal include your overall fitnessand blood pressure medication.How can I reduce my interdialytic fluid gain?The majority of patients who come for dialysis havesodium levels above 135 mmol/l. These patientsshould focus on cutting out salt to decrease IDFG, as itis almost impossible not to drink when your sodiumlevel is high. To quote Dr Charlie Tomson, ‘Askingpatients with severe thirst to drink less than one litre aday is illogical, inhumane, and should become part ofthe history of dialysis.’3Your osmostat only makes you thirsty if yoursodium level goes above your set point. For example,if you have a typical post-dialysis sodium level of138 mmol/l and your set point is also 138 mmol/l,consuming 16 grams of salt between dialysis sessionswill mean that you will need to take in at least twolitres of water to keep your sodium level below yourset point, as there are 138 mmol of sodium in eightgrams of salt. The water can be taken at any time andbe in any form (for example, tea, coffee, soft drinks, wine, soup, gravy or custard) that fits with yourpotassium and phosphaterestrictions. Drinks are usually low in salt, so most or allof the water they contain isavailable to dilute salt from othersources. However, some of thewater in fluids like soups and gravies is needed todilute the salt they contain. Figure 2 shows somemeals that have matching water and salt content.Whenever your water intake has not been enough to match your salt intake, your osmostat will be triggered so that you drink enough to return your sodium level to below 138 mmol/l. If yourwater intake is more than the two litres needed tomatch the 16 grams of salt, your pre-dialysis sodiumwill be a little lower than 138 mmol/l.If you are unable to remove two litres of fluidduring dialysis, you will have to reduce the amount of salt in your diet. Reducing your salt intake from 16 to 12 grams between sessions should mean that you can reduce your IDFG to less than 1.5 litres.Reducing the sodium level in the dialysis fluid (for example, to 135 mmol/l) can also help reduceIDFG, but you should discuss this with your doctor, as drops in blood pressure are more common withlow sodium dialysis fluid.Patient information BRITISH JOURNAL OF RENAL MEDICINE 2015; Vol 20 No 3Pre-dialysis sodium level (mm/l)Patient0 50 100 150 200 250 300 350115120125130135140145135n Figure 1. Pre-dialysis serumsodium (Na) levels of375 haemodialysispatients. Each barrepresents the rangeof six-monthlymeasurements in asingle patientFluid gainedbetween dialysissessions is mostlyextracellular fluidCopyright © Hayward Medical Communications 2015. All rights reserved. No unauthorised reproduction or distribution. For reprints or permissions, contact edit@hayward.co.uk71www.bjrm.co.ukA daily intake of six grams of salt, as recommendedby the UK Food Standards Agency, should result in anIDFG that most dialysis patients can tolerate. Manyfoods now have labels to show how much salt (orsodium) they contain, either in grams or as apercentage of this allowance. Your dietitian will beable to advise you on foods to limit or avoid, and howto read the labels.Should I have a daily fluid allowance and how do I monitor my fluid intake?If you want to decrease your IDFG but your pre-dialysis sodium levels are already low, cutting out salt may not be the answer. If you are thirsty because you have high blood sugar, you may needhelp from a diabetes specialist. If a dry mouth(xerostomia) is making you drink, your doctor may be able to prescribe a gel or spray. Your dietitian willbe able to help you to identify ways to reduce yourfluid intake.Trying to restrict your fluid intake can make you feel thirstier just because you are thinking about not drinking. Keeping track of the amount of fluid you have consumed is useful when trying to reduceyour salt intake as it can help you to identify mealsthat are high in salt. It is important to monitor thewhole period between dialysis sessions, as waterconsumed in the evening can dilute the salt in your breakfast the next morning.The easiest way to monitor your fluid intake is touse your IDWG: one litre of fluid gain will result in 1 kgof weight gain. Recently, dietitians at the dialysis unitin Southend have identified a small group of patientswith high fluid gains and gave them a chart on whichto plot their weight changes. The patients receivededucation on the relationship between salt and fluidbeforehand, but had no input from the dietitians oncethey started using the charts. After only two weeks,the average IDFG for the group had decreased from4.1 to 2.8 litres.4If you want to monitor your IDWG, make sure you get your actual post-dialysis weight (do notassume you finished dialysis at your target weight).Your IDWG will give the best estimate of your IDFG if everything else that affects your weight is the samefor the sessions before and after the interdialyticinterval. Ideally, you should be wearing similar clothesand have similar meals and drinks just before andduring dialysis nDeclaration of interestThe authors declare that there is no conflict of interest.References1. Lindley E, Keane D. Are haemodialysis patients at risk of excessive dehydration?Ren Soc Australasia J 2013; 9: 110–111.2. Mactier R, Hoenich N, Breen C. Clinical practice guidelines: Haemodialysis.Petersfield: Renal Association, 2009.www.renal.org/guidelines/modules/haemodialysis (last accessed 02/09/15).3. Tomson CR. Advising dialysis patients to restrict fluid intake without restrictingsodium intake is not based on evidence and is a waste of time. Nephrol DialTransplant 2001; 16: 1538–1542.4. Ramlan G, Chandrasekharan L. Fluid and salt dietary intake audit in patientsreceiving haemodialysis treatment. British Renal Society Annual Conference,Leeds, UK, 2015.BRITISH JOURNAL OF RENAL MEDICINE 2015; Vol 20 No 3 Patient informationn Interdialytic weight gain (IDWG) is theincrease in weight between the end of onedialysis session and the start of the next.n Although you may sometimes put on ‘real’weight, the weight increase between dialysissessions is usually due to the accumulationof fluid. This means that your IDWG,measured in kilograms, will be the same asyour interdialytic fluid gain (IDFG), measuredin litres.n For most patients on haemodialysis, the bestway to reduce IDFG is to cut down on salt-containing foods.n Monitoring your IDWG can give youcontinuous feedback on the salt in the mealsthat you have eaten between sessions,enabling you to identify foods with lowersalt content.n If your thirst is not due to salt intake, talk toyour doctor, nurse or dietitian, as there maybe a solution.Key pointsn Figure 2. Four meals and snacks with similar salt and water content: a bacon roll with ketchup, applejuice and a mug of tea with milk (3.2 g salt, 400 ml water); pepperoni pizza with side salad and a largeglass of soft drink (2 g salt, 250 ml water); buttered crumpet with jam and a white coffee (1.8 g salt,225 ml water); cheese with crackers and a glass of wine (1.4 g salt, 17  ml water) Copyright © Hayward Medical Communications 2015. All rights reserved. No unauthorised reproduction or distribution. For reprints or permissions, contact edit@hayward.co.uk

What I tell my patients about interdialytic weight gain

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What I tell my patients about interdialytic weight gain

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