Does Fluid Intake During Dialysis “Count” as Fluid Weight Gain?

This blog post was made by Dr. John Agar on April 16, 2020.
Does Fluid Intake During Dialysis “Count” as Fluid Weight Gain?

I was recently asked the following [edited] question:

“Do you include rinse-back and an on-dialysis drink in working out the amount of fluid to take off? Let’s say I gained 1 litre and thus have 1 litre to remove to reach target weight. But, I then (1) have a drink during dialysis and (2) include the fluid I use for rinse-back. Do I need to take off 1.5 litres? Or, just the 1 litre?”

This is a very good question, and there is no absolutely right answer to it. There are several variables that are hard to be certain about, but let me try to break it down without confusing the situation even more!

In the example, a 1 litre weight gain is pretty minimal for an adult. The heavier someone is, the less a 1kg (1 litre) weight gain is, relative to body weight. As most adults are somewhere between 55-100kg in weight, 1 litre is at most about 2% of body weight. Assuming that a dialysis session will need to be at least 2 hours long (for solute removal, regardless of fluid status), removal of 0.5 litres/hour (i.e., no more than 1% of body weight/hour) would not challenge the blood volume at all. Nor, for that matter, would removal of 1.5 litre over 2 hours (or more).

But, most likely gain more than 1kg (1 litre), and the more fluid there is to remove, the faster it must be removed in any given dialysis treatment. When fluid to remove is a volume greater than about 7-8 ml per kilogram of body weight per hour of dialysis, trouble starts. This is when the vexed issues of (1) fluid consumed during dialysis and (2) rinse-back fluid start to come into play.

Imagine that the amount to remove is 4 litres, and the treatment is a planned 4 hours. This requires removal of 1 litre per hour. This might still be a safe rate if the patient is heavy—but may already be unsafe if the patient is light. Ideally, fluid removal rates should be less than 7-8 ml for every kg of body weight in each hour of dialysis.

See how BODY WEIGHT influences ultrafiltration (UF) RATE. The first example table* uses the same amount to remove and same dialysis duration, but differing target weights.

*Note that ALL of the examples below are made up purely to illustrate points.

Target Weight

Fluid Gain

Time (Hours)

UF Rate

Outcome

Example 1

150 Kg

4 Kg (= 4 liters = 4000 mL)

4

(4000 ÷ 150) ÷ 4 =6.6 ml/Kg/hr

Safe

Example 2

100 Kg

4 Kg

4

(4000 ÷ 100) ÷ 4 = 10 ml/Kg/hr

Getting Dangerous

Example 3

50 Kg

4 Kg

4

(4000 ÷ 50) ÷ 4 = 20 ml/Kg/hr

Downright Lethal

See how TIME influences the UF rate. The second example table uses the same amount to remove and target weight, but differing dialysis durations.

Target Weight

Fluid Gain

Time (Hours)

UF Rate

Outcome

Example 1

100 Kg

4 Kg

6  

(4000 ÷ 100) ÷ 66.6 ml/Kg/hr

Safe

Example 2

100 Kg

4 Kg

4  

(4000 ÷ 100) ÷ 410 ml/Kg/hr

Getting Dangerous

Example 3

100 Kg

4 Kg 

2  

(4000 ÷ 100) ÷ 220 ml/Kg/hr

Downright Lethal

See how the AMOUNT TO REMOVE influences the UF rate. The last example table uses the same target weight and treatment time, but a differing fluid gain to remove.

Target Weight

Fluid Gain

Time (Hours)

UF Rate

Outcome

Example 1

100 Kg

2 Kg

4  

(2000 ÷ 100) ÷ 4 = 

5 ml/Kg/hr

Very Safe

Example 2

100 Kg

4 Kg

4  

(4000 ÷ 100) ÷ 4 = 10 ml/Kg/hr

Getting Dangerous

Example 3

100 Kg

6 Kg 

4  

(6000 ÷ 100) ÷ 4 = 15 ml/Kg/hr

Very Unsafe

So, should fluids taken in during dialysis and rinse-back fluid given afterward “count” when you calculate how much to remove in a given session? Let’s look at both.

  1. Fluids you drink during dialysis

    To a degree, it depends when you drink this fluid.  Early on in a treatment, your gut will likely absorb the fluid, so it should technically count. But, we (and many other dialysis services) suggest that you drink no more than a standard cup or tea (or the like) during a treatment, or about 180-200 ml. This is a reasonably small amount, and in the range of normal weighing error. Thus, we don’t count it as extra fluid to remove. If anything, it will add to the fluid gain for the next treatment. Certainly this is the case if you drink fluid at or near the end of a treatment. Then, it is clearly best to regard this as part of the fluid gained between treatments to remove next time.

  2. Post dialysis rinse-back

    This is clearly post-dialysis fluid, and should strictly be counted as the start of the next fluid gain.

In general, then, you would not want to remove the “extra” volume at a treatment. Doing so runs the risk of removing water that is not yet in your bloodstream. Pulling water that is not in your blood can cause your blood pressure to drop—which is not likely to be a good ploy. You would need to add water or even saline (water + salt) to correct the error, or you may have all of the symptoms and effects of volume depletion: 

  • Nausea
  • Vomiting
  • Dizziness
  • Clouded mental state
  • “Flats”
  • Organ stunning

The key variable to get right is your predialysis target weight. If target weight is correct, removing more water beyond that can reduce your blood volume. Of course, the real problem is that we really don’t know how to accurately measure a true and ideal target weight (in real time). For all that has been written about bioimpedance techniques, ultrasound to assess the vena cava or lung fluid status, hormone analysis, etc...none are practical at the clinic chair/bedside. And, they are certainly utterly impractical for home patients. Target weight is, in truth, still a clinical guess, though a wise physician and/or a well-trained home patient can get pretty close to it, most of the time.

I don’t think over-drying (i.e. removal of extra volume) is wise. It is better to try to get as close as possible to the assessed target weight and count any post-dialysis fluid return as the first gain for the next treatment. At the end of the day, do we know? Well, no! But, this is the best I can do to explain the inexplicable and advise the unadvisable.

Comments

  • Loylyn Jones Walton

    Jul 21, 2023 4:11 PM

    I did serious research affecting my dialysis debacle and found that too much fluid was being taken off. I experienced sweating, heart palpitations, severe vomiting and headaches, nausea of the worst kind, and writhing stomach spasms, along with popping veins in my legs and arms. The discomfort was as if someone was wringing my intestines from inside.
    My dry weight never changed for 6 months at 60.0 kg . That Thursday of my dialysis "incident" was 2.4. Kg/l for 4 hrs. It was the worst! ; Saturday treatment (upon explaining my incident) , the technician lowered the amount of fluid to be taken to 1.6 Kg/L where results were not so severe , but mitigated. I never weighed in 3 lbs or over my dry weight. I began jotting down dry weights in and out on recent treatment dates. Finally! At last adjustments this Tuesday upon my sharing the incident with the Clinical team! My dry weight was changed from 60.0 to 63.0 , fluid weight taken off changed from 1.6 kg/l to 1.2 Kg/L for 4 hrs. . What a huge difference from the adjustment to weight.
    I will also share the dry weights in and out . Tues weigh in 64.2, out 63.1 (difference 1.1 L); Thurs. weigh in 64.4, out 63.5 (difference 0.9!). I still experienced nausea and temporal headaches , however, the mitigation was to add fluids!
    I am not seeking reassessment of my kidney functions as positive changes are also occurring.
    Thank you so much for your dialysis resources! At best, it all may mean less time on dialysis and a higher percentage change in kidney function.
    I hope this helps others advocate for themselves.
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    • Beulah Thompson

      Aug 17, 2023 7:10 PM

      I was going through the same thing. I was getting pains in my hands, my arm and my leg and I started getting headaches. I believe they were taking too much dry weight and fluid off. I told them to stop and told them to start cleaning my blood because I became under weight. I have an appointment with my doctor to change this. I look like a crackhead my skin would turn dark after dialysis some days.
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    • Beth Witten

      Jul 21, 2023 4:39 PM

      Medical Education Institute that administers the Home Dialysis Central website developed an ultrafiltration calculator to help patients and staff know how much fluid is safe to remove during a single dialysis session. It's safest if you remove no more than 10 ml/kg/hr. You can do this by not gaining too much over your target weight, by lengthening the treatment time or adding another treatment if pre-dialysis weight is too much over the target weight. Here's the link to the calculator. Check it out. https://homedialysis.org/home-dialysis-basics/ufr-calculator
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  • Loylyn Jones Walton

    Jul 15, 2023 12:19 PM

    Your information on dialysis treatment was very helpful and insightful.
    My treatment was set at 3 kg/4hrs (the highest ever set!) to remove and my body crashed! I broke into sweats, my heart was beating fast, there was vomiting , nausea, dizziness, my legs were unsteady, the stomach cramping left me with no appetite for hours!
    Now I know the reasons why going above 2.5 was harmful. My target weight is 60 kg (I've been told) and I usually gain no more than 2.5 liters of fluid.
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  • Debra Howard

    Mar 29, 2023 1:43 AM

    I'm in dialysis for 3 months and they have not got my dry weight right. I was in hospital, then I started dialysis and have not checked my weight to see if it needs adjusted.
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    • Loylyn

      Jul 21, 2023 4:20 PM

      Please , if you do anything, ADVOCATE for yourself because you know your body threshold ! Everyone is different and what applies to the general treatment processes does not always mean it applies to you.
      Wish you the best!
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  • Michael C Harber

    Nov 22, 2022 7:31 AM

    I gained weight right after two hours of dialysis. Almost 1 1/2 pounds. Has never happened before. Alarm was not working during the procedure. Should I be concerned?
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    • Jennifer Ravert

      Nov 22, 2022 5:24 PM

      Hi Michael, if this is the first time it has happened, it is most likely due to a scale error either before or after treatment. Did you eat/drink during treatment? Administer a lot of saline? If you truly were heavier coming off than you were going on, the weight had to have come from somewhere. If that did not happen, the problem happened at the scale.
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  • Sara Slagle

    Nov 10, 2021 9:26 PM

    Home dialysis is doing great except my hubby has began being chronically hypotensive. I worry, annoy him. It gets down to 80/50 and once or twice lower. I know the rate cans go below 3. He’s very careful to mostly chew on ice, that’s all he orders at a restaurant. I’m thinking we’re pulling too much off or he’s eating at the wrong times.
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  • Sandy Lawrence

    May 13, 2020 8:12 PM

    Thank you for this simple pictorial easy explanation - Just Perfect to give to my patients [and colleagues], who have difficulty understanding &/or retaining verbal information/discussions. A wonderful resource to add to my repertoire - Kudos/acknowledgment to Dr Agar of course
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  • David Leong

    Apr 17, 2020 6:50 AM

    Thanks for the helpful information!
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