From fluid overload to volume depletion: tips on how to get it right?

The For Kidneys Sake podcast series is brought to you by Imperial College Healthcare NHS Trust and North West London Integrated Care Board (NWL NHS).

In this episode, Jeremy and Andrew discuss one of the most deceptively tricky areas of everyday kidney and general medical practice: assessing fluid balance. From swollen ankles to dizzy spells, from SGLT2-induced polyuria to the eternal mystery of the JVP, our hosts unpack why no single test ever gives “the answer” and why clinical acumen still matters. They explore how to distinguish true fluid overload from ankle oedema caused by amlodipine, when weight matters, and why blood urea creatinine ratios can occasionally point you in the right direction.

They also highlight the subtleties of recognising volume depletion, why 'dehydration' is often the wrong term, and how sick-day rules, medications, polyuria, and patient education all intersect in real life. From emerging technologies like smartphone perfusion video analysis to the humble power of a daily weigh-in, this conversation offers practical wisdom and a forward-looking perspective, a must-listen for anyone navigating the art and science of keeping patients neither too wet nor too dry.

Top 5 Takeaways

1. There’s no single test for fluid balance — Clinical assessment remains king: history, examination, serial weights, blood pressure (including postural changes), and context are indispensable.
2. Not all ankle swelling is fluid overload — Calcium channel blockers frequently cause ankle oedema that doesn’t require diuretics. Always consider medication effects before treating fluid overload.
3. Volume depletion is often subtle — Thirst, dizziness, polyuria (especially in CKD or after starting SGLT2 inhibitors), and weight loss are key clues, but each has confounders.
4. Simple tools beat fancy tech (for now) — Trends in weight, postural blood pressure, and blood urea/creatinine ratio often outperform bioimpedance machines or wearables in real-world clinical value.
5. Prepare patients with sick day guidance — Clear, proactive advice about temporarily holding RAS blockers, diuretics, or SGLT2 inhibitors during vomiting/diarrhoea prevents avoidable AKI.

Resource Links:
NICE GUIDELINES [NG203] chronic kidney disease: assessment and management Overview | Chronic kidney disease: assessment and management | Guidance | NICE

Northwest London CKD guidelines for primary care Chronic kidney disease (nwlondonicb.nhs.uk)

Pumping Marvellous | The UK's Heart Failure Charity

The purpose of this podcast is to inform and educate health care professionals working in the primary care and community setting. The content is evidence based and consistent with NICE guidelines and North West Guidelines available at the time of publication.

The content of this podcast does not constitute medical advice and it is not intended to function as a substitute for a healthcare practitioner’s judgement.

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Transcript

Jeremy Levy 

Hello, I'm Jeremy Levy, consultant nephrologist at Imperial Healthcare NHS Trust. 

Andrew

And I'm Andrew Frankel, a colleague of Jeremy's, also working at Imperial College Healthcare NHS Trust. And welcome to another podcast in our series for kidney's sake. 

Jeremy Levy 

Indeed Andrew, yes, and it's so good to talk again. And today we're going to talk about fluid balance and fluid assessment, which we haven't talked about before. And we've picked this topic because we've been asked this question by quite a few listeners. So we're going to talk about why this is important, what's helpful for clinicians in primary care, is there a right answer for too much fluid, not enough fluid inside patients? How do we know if patients are? or fluid overloaded. 

Andrew

Yes, Jeremy, well, I'll start with the easy bit. And the easy bit is the message that there is no one test that gives the answer. A lot of this is about clinical acumen, although really at a fairly straightforward level. But you need to see the patient in the flesh quite commonly, take a good history and look at serial markers, including blood pressure, weight and some biochemistry.

Jeremy Levy 

course. 

Andrew 

But many of the parameters that we talk about also have other explanations too. And that complicates things and this makes it much harder, particularly to do by remote assessment by video or telephone. But not impossible, as exemplified by the fantastic work the Community Cardiac Failure Team undertake. But I'll stop there and let you now deal with the harder bits, Jeremy. 

Jeremy Levy

It's always the case, Andrew, give me the difficult work, you take the easy bits. So, okay. Firstly, and particularly in the elderly, I'm gonna talk a bit about ankle swelling. Because ankle swelling, of course, might mean people are fluid overloaded and have got too much fluid on board, but may not. And of course, everyone listening to this podcast will know that, for example, calcium channel blockers such as nifedipine and amlodipine cause ankle swelling. It's almost universal, isn't it? 

Andrew  of course. 

Jeremy Levy  And on that topic personally, I never increase amlodipine above 5mg since it always then causes ankylodema with absolutely no additional benefits above 5mg for the kidney or minimal improvements in blood pressure control. But that's sort of a different matter. And it usually doesn't need treatment does it? Ankylodema from calcium antagonists doesn't. If people are eating a lot of sodium you could reinforce a low sodium diet. But other than that, ankle swelling is an important issue. And ankles swelling, edema, edema rising above the ankles to the knees can of course mean that patients do have excess fluid, fluid overload, which might need managing. And this isn't usually just a bit of puffiness around the ankles. It's usually significantly more than that. And these patients would, if you examine them, usually have a raised jugular venous pressure, JVP. but this can be hard to detect, we all know that. So clearly in hospital we can do a chest x-ray very easily, but actually just listening to the chest is important because you can detect pulmonary edema as we all know relatively well if you were to listen to the chest. But in this situation where you've got sort leg swelling and possibly pulmonary edema or fluid in the chest, you do need to think about the diagnosis as well as treating because even though the treatment might be relatively simple, for example, start diuretics, You need to think about is the patient on drugs that may be making this worse, particularly non-steroidals, which can cause sodium retention, but also about the diagnosis. 

Andrew 

So Jeremy, actually that wasn't too hard and there were some really simple messages there. Completely agree with you with everything you've said, of course. Including your comments about amlodipine or calcium channel blockers, which is my policy as well. And where you do not need or indeed should not use diuretics to manage the ankle swelling. I would just say also, if you've got someone on 10 milligrams of amlodipine and they haven't got ankle swelling, one of the first questions is, are they taking their medicine? But let's get back to where you identify genuine lower limb oedema associated with fluid overload. You'll want to consider the possibility that there's heart failure. And we now have fabulous new treatments for this, and we really need to be making that diagnosis. When it comes to heart failure, I've also found it really useful to use the resources on the heart failure related website called Pumping Marvelous, where they define the key questions to ask the patient to help screen for heart failure. They call these the beat questions, breathlessness, exhaustion, ankle swelling, and time, i.e. over what time has it appeared. Thereafter, if you're thinking of heart failure, a BMP blood test is a good screening test to help determine whether you need to move on to order an echocardiogram or ask for a cardiac opinion. 

Jeremy Levy

That's really helpful. I've not come across that, the beat questionnaire and pumping marvellous, particularly the website. I'll remember that. So that was sort of fluid overload and ankle swelling and a quick way of thinking about that. Let's move on now to think about dehydration or a much better term as you remind me actually, ⁓ fluid depletion. And here again, we're going to get a bit back to basics and be accurate. Dehydration, of course, would mean loss of water predominantly from the body. but most people will have lost salt and water and it might be from diarrhea or vomiting or sweat so it's not really dehydration if we're being absolutely accurate. So thank you Andrew for reminding me of that. thinking about sort of volume depletion and the first thing to think about is thirst. Thirst is an important part of the history. It can be a sign of volume depletion. Of course there are other things also that do it but it's important. As can dizziness. Dizziness might indicate volume depletion. especially postural dizziness. But again, a bit like thirst, there are multiple causes for all of these symptoms. And in some patients with significant chronic kidney disease, they can become polyureic because their kidneys don't concentrate urine effectively and they therefore essentially lose too much urine for what they're eating and for their physiology and are at risk of becoming volume depleted and with symptoms, postural hypotension and some weight loss. And then... While we're thinking about causes, after starting an SGLT2 inhibitor, Dapaglifazin, Empaglifazin, Cannaglifazin, some patients can get polyureic and may need to stop or reduce the dose of their diuretics. It's often a transient effect, but it can be important. So clinically, you've thought a bit about this. What are you going to examine somebody for? The postural drop in blood pressure is really important clue. That postural drop is often practically slightly harder to do, meaning blood pressure. sitting or lying and then standing because actually people can maintain normal blood pressure even if they're quite severely volume depleted and so you might not pick this up if you just measured a single sitting blood pressure for example. But again the challenge here, medicine is about clinical challenges isn't it, is that if you're a diabetic with autonomic neuropathy you may well have postural symptoms and postural hypotension so separating that from volume depletion can be hard but that's where clinical acumen comes in and thinking about these various different possible causes of a symptom. And then finally weight change. Clearly weight change can be very helpful because if you've got polyuria, if you're losing salt and water from diarrhea or vomiting or any other cause you're likely to lose weight. So short-term changes in weight are likely to be fluid shifts not fat shifts and that's what happens in heart failure clinics. We encourage people to weigh themselves daily don't we to help manage their diuretics against their symptoms. 

Andrew  

Yeah, absolutely. And that's a really powerful way of monitoring fluid changes. And then I want to just clarify here with you, Jeremy, there's no simple blood test or simple investigation that helps here. 

Jeremy Levy  

If only, Andrew, ⁓ and indeed no. There is a clue from blood testing which is actually very helpful. So if you've got a blood test and you look at the blood, urea and creatinine and actually look at the ratio of those two. It's not produced as a ratio in the report, but you've got in front of you the serum urea and the creatinine. Normally, for example, the creatinine might be 100 micromoles per litre and a urea say five, these are normal figures. So that's about a 20 to one ratio of the creatinine to the urea. In dehydration or volume depletion, the urea might be say 15, but the creatinine still 100. So that ratio is no longer about 20 to one. So a relatively higher blood urea to a blood creatinine can be a really, really useful clue to volume depletion. But of course, you don't need a blood test from six months ago. You need a blood test on the day you're assessing the patient. And that can be hard in primary care. So that ratio, the blood you read, the blood creatinine can be a clue. And then technologically, we all hope for sort of a magic machine that will give us the answer. And you'll see, people may see some advertised things called bioimpedance or bioelectrical impedance devices. And that sometimes wraps up in body composition analysis machines. And they try and tell you that they can assess volume depletion. The reality is that they're not very accurate in determining true hydration states and they don't give an answer that simply says you need one or two litres of extra water. And then lastly, course, the urine. certainly if you have volume depleted, your urine becomes much more concentrated, darker. And if you were to measure the specific gravity, it goes up. But again, there can be other causes for that. But the combination of those things can be useful. So sadly, there isn't one test. No. 

Jeremy Levy 

but we would hope that things might improve. And I've been reading recently some fascinating approaches using new technologies. For example, people, can get your smartphone to actually, the camera on your smartphone to record a video of your fingertip for between 15 and 30 seconds. And actually it gives a pretty good marker for dehydration. What it does, the AI in the phone and the video looks at variations in the peripheral blood volume. And that is a marker of hydration. It's not yet proven but there's been some interesting data. And smartwatches, some smartwatches measure sweat generation, they tie that with your pulse rate and the optical measures on the back of your smart device or smart phone, smartwatch rather, and that can give a clue to hydration and dehydration but none of them are very accurate yet and have got lots of confounders. 

Andrew  

Gosh, so we really are moving into the world of Star Trek and I think you're right that we're going to see in maybe two, three, four years time, primary care having on-site very simple machines that actually look at capillary flow and fluid assessment. That will happen. The meantime, as you say, the bioimpedance methods aren't quite accurate enough. I know my personal trainer uses it to measure my, not my fluid, but my fat. That's always very depressing. However, whilst we're still talking volume depletion, I do think, as you mentioned, the history is all important and that doesn't need AI or smartphones. Well, it's very important to prepare patients when starting new medicines, such as ACE inhibitors and angiotensin receptor blockers, to prepare them for managing their fluid status. And this is all wrapped up in what we call sick day guidance, which I know we've talked about before on these podcasts. I warn patients that if they get illness, which means they can't drink or have vomiting or diarrhoea, they just hold or omit. I try not to use the word stop these agents, RAS inhibitors, ACE and ARBs or other blood pressure medicines or diuretics for a couple of days, but then restart when they are better. And you're right about the SGLT2 inhibitors. They can make people pass more urine in the initial phase. which can risk dehydration. But that usually only occurs when people have very high blood sugars and good kidney function when they start the treatment. Jeremy Levy (12:31) Yeah, as always, we agree on everything Andrew. So when assessing fluid balance, is, you the history is really, really important. We can then assess blood pressure and ideally postural blood pressure, review their body weight and trends in body weight. And ⁓ that we've talked about and it's very, very useful. And then not to be confused, we're talking about body weight. Lots of patients, of course, trying to lose fat and using GLP-1 receptor agonists. and they may not be prescribed. Lots of people are buying Manjaro and the alternatives. So weight is important, but think about all the confounders. We've been talking a lot about fluid balance and I know that we haven't mentioned actually an ideal amount for people to drink and our boss, Joanna, has told us we must talk about this. So how much should people drink? Well, there isn't an absolute number, but advice that people should drink three litres a day is far too much for almost everybody. unless they've got kidney stones, which is for a different day. And the amount usually is about one and a half liters for most people. But it does depend on where you're living. Clearly, if you're somewhere hot or with air conditioning, you might need more. And in most countries in the summer, to drink a bit more for those very reasons. But that would be an amount that for most people would be normal. 

Andrew

And a curveball here, Jeremy, because I get asked this really often. What do you mean by how much they should drink? What fluids count? 

Jeremy Levy  

Another great question Andrew. So it's any fluid isn't it? So that's not just the morning coffee, tea and a glass of water. But if you have soup for lunch and dinner, that's fluid. There is of course fluid in other foods but that won't count. So it's definitely fluid that looks like fluid. But that would include soups, teas, coffees, hot chocolates and water. But not the water that's tied up in your apple. 

Andrew 

Excellent. I'm often asked about the tea and the coffee. So before we finish, I want to just remind the audience about a couple of things. First of all, something that we've mentioned before, that when you start an SGLT2 or a RAS inhibitor, you will get a drop in GFR, which is expected, and you only need to check kidney function for the RAS, not for the SGLT2 inhibitors. That is aggravated if you are volume depleted, that drop. So that's worth remembering. And then diuretics. There's a term used about diuretics of them being nephrotoxic. They are actually rarely nephrotoxic. If people with CKD or heart failure or other cardioreno metabolic disease need diuretics for blood pressure or fluid overload, they can be used even if they have significant CKD. This may cause a small drop in GFR but that can still be helpful if they improve the physiology and they improve the state of fluid overload. They don't need stopping in CKD just because the GFR is falling slowly over the time because it's usually the underlying disease that's causing this and not the diuretics. Unless you overtreat the patient and they then become chronically volume depleted, that's the only time to hold back. in that circumstance. 

Jeremy Levy 

That's really important Andrew. I see a lot of patients where their GFR is dropping but it's a predicted trend and then somebody stops their diuretics because they must be the cause of the problem and then of course the patient runs into problems with fluid retention. So I think we've covered fluid balance haven't we? What we want is somebody out there to come up with a single test that gives us the answer and an easier way to assess fluid balance and we should watch this space across wearables and smartphone tools but we're not there yet. 

Andrew 

Yeah, AI will solve it over time. But for now, Jeremy, when thinking about fluid balance, my takeaways are always prepare patients when starting or reviewing medicines, be clear about giving them good sick day guidance, and importantly, not just when to pause the medicines, but when to resume them. Secondly, history is important when considering fluid balance. 

Jeremy Levy 

Such optimism. 

Andrew 

and then use simple clinical measures such as postural blood pressure, weight trends, and the presence of peripheral oedema. And diuretics are useful when managing fluid overload. They rarely cause kidney problems unless the patient is actually already volume depleted and you still continue them. Then they can cause some degree of CKD. 

Jeremy Levy 

That's been great Andrew. Thanks, good summary as always. I hope this has been a useful chat. We should leave everybody to get on with their lives and listen to the next episode. 

Andrew  

Yes, and do also listen to some of our previous episodes if you haven't. They're all available on your favourite podcast stream or from our website. And do subscribe to our newsletter as well to hear about future and indeed past podcasts. 

Jeremy Levy  Bye.