How do they calculate dry weight?

[Des]

How  do they calculate dry weight? Is there a formula or is it just a case of "How low can you go"?

I really need to find out. I think it is a guessing game as they don't use any fancy machine to measure the "fluid" in my body at all.

What do they do when you pick up or loose weight?

I would like to here from everybody but the techs or staff might be able to shed some light on this for us.

  

[Bruno]

Gee Des, add me to this thread because I've often wondered the same thing. I mean, if you have put on 2 kg since the last session you have 2 litres to take off...but what about if you know only 500ml was fluid and the rest was solid food you over ate.
And what if you genuinely lose weight but your IW isn't changed...you would end up constantly taking of less fluid than you should...and carrying more in your system than you should.
I'm 110 kg and keen to lose weight but not sure how to go about it, let alone know if I'm successful.
I reckon its all hit or miss.

[Desert Dancer]

Hi, Des and Bruno -

From what I understand it's pretty much just a guessing game; you don't know if you've gone too low until you start having symptoms of low blood pressure (cramping, dizziness, etc.).  When I started D, they discharged me to in-center with a dry weight of 68.5, which I knew was too high. But I could never take off more than 1500mL in-center because the UF rate was too fast and made me feel bad. Same thing with short daily, though I did manage to demonstrate my dry weight was at least 66 by staying around that weight with no symptoms of being too dry. Now that I'm at home I can take off as much as 2800mL of fluid (maybe more), and my dry weight is somewhere around 63. That's the middle of the 5-pound range I've maintained all my adult life, so I probably won't chance taking off any more fluid. I don't really need that precise an indicator of my real dry weight, thank you! 

Of course, I may have to raise my dry weight again after Thanksgiving...

[RichardMEL]

In general it's an educated guess.

However there are ways to make it more accurate. Two ways I know of.

1. There's a body mass scale thing our unit has. It's like a regular set of scales but it (somehow) measures the % of fluid in the body. From that they can get an idea of if you're too dry or too wet.

2. The BVM(or "crit line" if you prefer) - done through the HD machine which measures the "refill rate" of fluid into the bloodstream (again I have no idea how this is done, probably as a percentage of plasma in the blood flow or something like that) - if it's over 90% then there's too much fluid (too wet), if under 90 then things are too dry (and thus the dry weight needs to be upped). Usualkly it's measured over the period of a treatment, and at least in my unit, in conjunction with UF profile 5 or 6, which have "rests" to allow the body cavities to refill. At the end of the treatment based on where it's at you have a fair idea if fluid is being carried.

I've seen BVM used when folks have trouble breathing and thus the presumption is that too much extra fluid is onboard (I saw one guy at 102% at the end of his treatment - and no I don't know how you can get over 100!). He was quite overloaded I understand.

However most units just make an educated guess in terms that you come in and start with a baseline weight, then fluid is taken off, say 1kilo or maybe less, and basically based on how the patient reacts - BP going low, through to crash or cramp, they realise they've gone too far - yes, the "educated" part of the guess is the result of discomfort to the patient. Not very nice, is it?

KICKSTART knows much more about the BVM as she does it every session - she's the expert.

As for what I do with my own weight management... after 4 years I get a feel for where I am at. I watch how my BP goes during treatments and I consider my weight change between treatments, if I'm exercising more etc and make an educated adjustment every so often. I just changed mine by 300grams the other day, but my next treatment my BP was a little lower than usual, so I am starting to wonder if I should have just left it where it was. No cramps though, so we'll see. It's summer and I tend to eat a little less when it's hot, and I am exercising a bit more, so I felt I should take a little off my Dry Weight, but maybe not.. so even I am making educated guesses. In general it's easier to leave it alone if no major changes are going on.

I think the times when it can really become difficult are if there's a big change - say a hospital admission with no exercise, or maybe no food, or whatever that might result in a substantial weight change one way or the other. Luckily I haven't had that happen yet (touch wood) but I can imagine that you'd need to re-evaluate when in that sort of situation.

[Bruno]

Today I found another indicator...a dry cough, particularly when you lie down. I went to my doctor , told him I had a cough, worse at night in bed, but no cold or flu' symptoms. He checked my lungs, said I had some fluid in them and then went on to say that with some people, instead of fluid collecting around your ankles and other places, it can collect in your lungs.
This ties in with the fact that I've thought for some time I might be carrying extra fluid because I come off dialysis with good blood pressure and never go flat...I've thought I'm too far away from the wall. Also, a few days ago I went below my IW with no problems, .3 kg. Not much, I know, but an indicator at least.

[Rerun]

Dry weight is your true weight minus any extra fluid.  So, yes it is a moving target and changes when you lose or gain true weight.

Sometimes you just have to challenge your fluid and take more off and if you do well then next time take more off until you lose blood pressure or feel bad.  It sucks!

[YLGuy]

Yes, it does.  Yesterday, with 20 minutes left, all of a sudden my left leg cramped bad.  It was in the calf and my shin.  The tech let me stand up to stretch but then I felt sick to my stomach and dizzy so I had to sit back down in a lot of pain.  My tech said that he had not seen me cramp that bad.  I told him about the last center where it took 4 techs to hold me down my cramping was so bad.  I guess I gained a little weight during Thanksgiving.

[Bruno]

That's true YL Guy, but I've realised the reverse must be true as well...by that I mean if you do session after session with no fall in BP, and if your BP after the session is the same as when you went on...well, perhaps you are carrying a little too much fluid.
And I just thought of another...what about if your BP becomes consistently a little higher than normal? Could you be pushing around a little more fluid than you should?

[Stoday]

I think that if you were carrying too much fluid you'd notice it — as oedema around your ankles, legs face etc.

[Bruno]

I'm only talking 500ml...750ml tops...and my ankles have never showed much fluid build up.

[greg10]

That's true YL Guy, but I've realised the reverse must be true as well...by that I mean if you do session after session with no fall in BP, and if your BP after the session is the same as when you went on...well, perhaps you are carrying a little too much fluid.
And I just thought of another...what about if your BP becomes consistently a little higher than normal? Could you be pushing around a little more fluid than you should?

Yes, higher BP during dialysis is called intradialytic hypertension and it is often the result of poor fluid control to the high side, it is a well known effect of too much fluid.  Intradialytic hypertension happens in about 15% of hemodialysis patients, so it is less common than hypotension.

[RichardMEL]

My fluid tends to collect around my waist for some reason, though post transplant it was all over (my ankles and feet were horrible for a week or so) but then again I was like 5+ kilos overloaded but slowly that has come down and I'm around 1-2kg over.

Bruno did you challenge your Dry Weight (ok IW) to take it down a bit to see if you can get some of that extra fluid off? Collecting around your lungs is a little scary and I would have tried to get that extra out if possible (I know this was a month or so back... how is it now?)

[M3Riddler]

How  do they calculate dry weight? Is there a formula or is it just a case of "How low can you go"?

I really need to find out. I think it is a guessing game as they don't use any fancy machine to measure the "fluid" in my body at all.

What do they do when you pick up or loose weight?

I would like to here from everybody but the techs or staff might be able to shed some light on this for us.

 

There is no formula to calculate dry weight. There are various methods that one can use to determine your dry weight. In my opinion, it should be up to the dialyzor to figure out one's dry weight and not the doctor as they may tell you a number at clinic etc... and then you may not see them for another month. Just because your neph states that you are for example 65 kilos for your dry weight does not mean that this is what you are going to be all month. Your dry weight changes, sometimes daily. This is why the patient should be invovled and determine their own dry weight. 

For those on home dialysis, it should not be much of an issue if you are off too much since you will be dialyzing the next day. For those in-center, this can be more of a challenge since you will have a day and sometimes a weekend of gaining fluid.

Your dry weight is influenced by anything from the fluid you drink, the meals you eat, the time of day you weigh yourself ( you weigh less in the morning than at nite) and even your activity level.
Some ways to determine if you are or have reached your dry weight are:

Higher Pulse - Greater than 95 towards end of treatment
Lowering of blood pressure
Cramps
Washed out Feeling ( can also be due to pulling too much fluid off too fast)

I normally go by my pulse and blood pressure. As soon as my pulse starts going up - usually towards end of treatment, i know I am close to or at my dry weight and stop ultrafiltation.

There is a blood test that can be performed to determine if you are fluid overloaded. This test is called a bnp. It is normally used for cardiac patients but can also be perscribed by your nephrologist to determine if you are fluid overloaded.

///M3R

[Bruno]

Yes, I did challenge my dry weight Richard and I got a real surprise. I'd slowly brought it down by a full kilo (1000ml) after the doctor told me the dry cough was excess fluid and many accumulated it in the lungs before the anklles.
Then, one of the home support nurses told me I was carrying at least 500ml on my back and I could go further (which I did) and lost another 1 kg (1000ml).
My problem, if you could call it that, is that I've never had a cramp, so I'm still not sure I might have a bit more fluid.
One thing is certain, you need to walk up to that wall very slowly.
Good luck with your kidney, by the way, and it's so good to see you back and please stay with us. You are one of the strengths of IHD and if you have ever wondered about living a worthwhile life, don't worry, you are one of the few who have given vastly more than they have received.

[talker]

How  do they calculate dry weight? Is there a formula or is it just a case of "How low can you go"?

I really need to find out. I think it is a guessing game as they don't use any fancy machine to measure the "fluid" in my body at all.

What do they do when you pick up or loose weight?

I would like to here from everybody but the techs or staff might be able to shed some light on this for us.

 

There is no formula to establish ones dry weight.
From the very first time you weigh in at the dialysis center, you are setting a future starting point for a dry weight in Kilograms doing dialysis.
(1Kg=2.2 pounds)

Now begins the fun part. (oh boy, fun part!)

Formulas only kick in (start) after the dry weight is established.

When things were normal, and before starting any dialysis sessions, did you easily lose or gain weight ?
If yes, you are going to experience problems of some sort.
If no, you may still experience problems of some sort.
The yes and no above is what is commonly called 'between a rock and a hard place'.

Little things like clothing, shoes, and what's in your pockets, take on a whole new meaning when doing dialysis.

Even adornments, watches, and eyeware, take on new meanings.

Not trying to scare or frighten anyone with the above, just making you aware of what can change your dry weight.

When you step on that scale it should be the 'same' you every time with 'what' you are carrying at this weigh-in.

Water and body wastes that ones kidneys does / doesn't filter, will have the dialysis machine doing the job.

Body wastes filtered out , generally will not be a concern at this point.
BUT any water, poses a unique situation.
Water is in the blood. Water is in the cells of the body. Water is between the cells of the body.
Here is where to much to fast equals cramping or a hurt in the body.
Water in the blood normally is not the problem in giving cramps or hurt.
Water in or between the body cells that needs to migrate to the blood, is when you can experience the mother of all cramps.
One should call the dialysis technician to make machine adjustments at the first sign of cramp or vision changes.

Anyway, once I became aware that there is no need for cramps or vision changes while on dialysis, the whole event became more tolerable.

Energy levels after dialysis can take a nose dive for one or two hours.
At my age, (88) I'm more fortunate than many, I eat a small meal and take a short nap.
More can be said here of course, but will let that be another future talker tale.

talker

[iolaire]

In Singapore the Doctor said they had some sort of device, which sounds like a full body scanner, that could produce a true dry weight with no guess work.  Is anyone aware of such a device?

[kristina]

In Singapore the Doctor said they had some sort of device, which sounds like a full body scanner, that could produce a true dry weight with no guess work.  Is anyone aware of such a device?

Hello,
Is anyone aware of such a device {as mentioned (above) by iolaire} to estimate our dry weight more precisely ?
Many thanks from Kristina.