With diminished ability to take in fluids, how does one avoid dehydration? What exactly is dehydration and how much fluid minimum must one take in in a day to prevent dehydration? With nocturnal txs there is a lack of thirst, so how does one take in fluid if not thirsty while at the same time feeling almost full? Maybe there is a better way to ask these questions. I know you will straighten it out.

Easter Camp: Answer 6th April

Dear Jane

I seem to have answered similar questions to this on many occasions at this site.

I have done webinars on fluids and fluid balance.

I have done a monthly fact sheet for HDC on exactly the same issue.

I have explained why the various modalities (types) of dialysis have different impacts on the ability of the body to balance the fluid across the three main compartments in which body fluid is contained: the intracellular compartment, the extracellular compartment and the extravascular compartment.

As some of these explanations have been here, in these Q&A sessions … please first look back to an early question of yours - and my answer to it - on the advantages of nocturnal dialysis.

I have also explained similar concepts in some of the sections at my website: – see the ‘Dialysis Issues’ section in particular.

Firstly, can I suggest a revisit to some of these ‘prior attempts’ of mine at explaining ‘fluid control’.

However, I will try once again to explain fluid balance in the simplest terms I possibly can. If, at the end of this answer today, you still have trouble understanding these concepts, then maybe you will need to seek an alternative explanation from others.

The human body, in fluid terms, is a system normally in balance. But, before we think of the human body again, let’s try thinking of another fluid system. Think of a river system. A river is normally ‘in balance’ (or in harmony) with its surrounding countryside and with the things that live within it or which are nurtured by it.

But, things can go wrong with a river system.

At one end of the spectrum, it can rain, and rain, and rain. This will lead the river to swell with water (fluid) and eventually break its banks. The countryside that is normally nurtured by the river will be flooded and damaged. The creatures that live in or beside the river will be swept away or harmed. This is a river that is now ‘out of balance’, ‘out of harmony’ … it is in flood. This is a river (or system) which now contains too much water (fluid). It is engorged. In a word … it is drowning.

Think of the opposite end of the spectrum for the same river. The sun shines, and shines, and shines. There is no rain. The land dries out. The water in the river evaporates and no new water is added to wet the system. The land that is nurtured and depends upon the river for its life, dries out. Plants die. The creatures that live beside and in the river also die as the river dries up. This is a river that is now water (fluid) depleted … it is a ‘dehydrated’ system.

Dehydration means, simply, the loss of water (fluid) … and this is a river (or system) that has lost its water (fluid).

The human body is no different. Normally, the body is in balance with just the right amount of fluid within its 3 main fluid compartments (see earlier posts and the webinar) to nurture its cells and to allow free and normal function. It is a system in balance … it is ‘in harmony’.

If too much (excess) fluid is added to any system (river or body, to use my two examples) - or, alternatively, too little is allowed to drain away and escape - the system will flood and become engorged. This is fluid overload. At the other end of the spectrum, if the system dries out - too much fluid is removed or too little fluid is added - the system is starved of fluid. It then becomes dehydrated.

The body is just one such ‘system’. In most situations, it remains in balance, in harmony. It even has a number of inbuilt ‘control’ mechanisms to help this balance to be maintained, even when things start to go a bit wrong. But, despite its efforts at control, the body can still become fluid-depleted if too much fluid is removed or too much is lost … or too little is added back. This can occur either

• artificially, by excess fluid removal by processes such as dialysis


• through excessive losses of fluid from the body surfaces (by the loss of sweat, during fevers or in situations like burns)


• from body cavities (from the gut … as in diarrhoea or vomiting: from the kidneys … as potentially may occur with diuretics or in certain kidney diseases (like uncontrolled diabetes or certain tubular diseases of the kidney) where excess fluid can be lost: or even from the lungs … through evaporation or when a respirator is in use in an ICU).

• Sometimes, for example, if we cannot drink or take fluid in normally from the gut (as we usually do) … this may happen after surgery, have a high fever or if we are very unwell … then fluid replacement is required by other means (for example by an intravenous drip) and if this fluid replacement falls behind, inadequate fluid replacement may be a further complicating factor.

Whatever the case, whether it be excessive loss or inadequate intake, fluid balance can be disturbed.

Just like the river in a drought, the things that are normally nurtured by the normal fluid balance of the body become starved of fluid. They dry out … just like the plants do at the edge of the drought stricken river or the creatures that live in it will do as the water evaporates.

Fluid balance is just so important!

You asked in your question … 'with diminished ability to take in fluids, how does one avoid dehydration? … but, to me, the premise of your question is quite the wrong way round. Remember that in a dialysis patient, it is generally the diminished ability to excrete fluid that leads to the necessity to reduce intake … and not a diminished intake which then risks dehydration. Not a lot of dialysis patients face the risk of dehydration (except acutely during dialysis) … and even then, that is primarily the risk of an acute volume contraction in only the intravascular compartment … again, please see my previous webinars and HDC ‘Topic of the Month’ contributions to better understand this. Not many dialysis patients ‘dessicate’ … but a goodly number ‘drown’. Most have trouble with not drinking too much. Few complain that they cannot drink enough.

Thirst is another matter. Thirst is turned on if fluid is removed rapidly from the intravascular compartment … this was explained at my website and in a previous webinar in which I believe you participated … but thirst is not the same as dehydration. Thirst is a symptom. Dehydration is a body state.

You are right … nocturnal dialysis patients dont get thirsty. Why? … because there is no rapid contraction of the intravascular volume (as commonly accompanies conventional dialysis) and thirst is thus not switched on. The thirst that follows conventional dialysis is not due to dehydration … indeed, the remaining two compartments are often still ‘over-full’ or ‘flooded’ … it is simply due to too great a (temporary) reduction in blood volume for, by and large, ‘fast’ dialysis ONLY accesses the intravascular compartment.

While the two extremes of fluid balance in the human body are fluid overload and dehydration, in either case, the normal harmony and balance between the three body compartments and the fluid contained within them is disturbed. When this happens, body function is disturbed.

To answer your question about how much fluid should be taken in to avoid dehydration (and I have just made the point, a few paragraphs up, that most dialysis patients are more of risk of being ‘too wet’ than ‘too dry’… and again, Jane, you are seeking from me a finite number … a limit, a ‘minimum’.

Physiology varies so much between individuals of different body size, shape, age, sex, health or disease and environmental circumstance that it is utterly impossible to answer a question about a set ‘minimum’. I seem to recall that we have been through this before.

Any minimum (or maximum) for you, as an individual, is NOT going to be the same as the minimum (or maximum) for another individual. That is what is so unique about each and every one of us … we are all different. We have different ‘set points’, different ‘requirements’, different ‘break points’.

As I do not know you, I have no idea of the things that might impact on you, an individual, as opposed to any other person.

But … your team DOES know you. They know your size, your age, your shape, your habits, your ‘requirements’. They know your weaknesses, your strengths. They know your disease - and they know your treatment. They live with you in your environment. They, and only they, can answer questions of minimum (or maximum) … for you … the individual Jane. Ask these questions of your team - not of me. Any answer I might give, without a detailed understanding of you, the individual Jane, could be shamefully misleading … not only to you, but to others who might read these answers.

For example, on the question of fluid ‘intake’ … the amount of fluid that a 38kg, 90-year-old bed-ridden woman in an Alaskan winter will require to remain ’in balance’ is clearly going to be different to the amount of fluid that a 150kg, 25-year-old Sumo wrestler in a steamy Japanese summer will require. The absolute amount will be clearly different. The balance between intake and loss will be wildly different. These are two different individuals in two different environments.

Jane, even the amount of fluid you, personally, will require to remain in balance will differ between winter and summer. This would hold true, regardless of whether you have normal kidneys or are on dialysis. There is no ‘minimum’. There is no ‘maximum’ … these vary according to circumstance! Circumstance includes not only the shape, size and condition of the body itself but also the environment in which that body is existing – at that time!

I still doubt that I have put all this clearly enough - and, if so, I am sorry. Nevertheless, it is the best I can do. You have asked similar questions many times and I feel I have given many similar answers. That is because this is the only way I can answer these questions. I cannot do more.

Perhaps if you are still uncertain, and if you still seek answers that I am not giving or cannot give, you should consider seeking them elsewhere. In the many discussions around this issue that I have had with you and others at this site, we seem to have covered this ground many times.

But … can I suggest that you return to the fluid fact sheet I wrote for HDC’s ‘Topic of the Month’ back in 2008, to the webinar I gave for HDC on ‘Fluids and Solutes’ (Part 2) in 2009, to my website where I discuss the impact of dialysis on fluids (and of fluids on dialysis) and also to some of the many questions that have been asked about the difference between the impact of (1) long, slow, frequent dialysis regimes (eg: nocturnal dialysis) and (2) the shorter, less frequent conventional dialysis options on the ability of the body to adjust and sustain fluid balance.

I don’t wish to sound ’testy’ or unkind, but it seems that the same questions keep coming up. If my answers have still not been adequate, then I apologise, but I have done my best.

Good luck and best wishes

John Agar