Dry weight

Dialysis is a key treatment approach in patients with advanced chronic kidney disease. As we explained in this comprehensive Dialysis Guide before, Dialysis is a method to “partially” assist unwell kidneys with their overall blood-balancing activities. It does so by removing excess fluid and clearing out metabolic waste build-up in the blood alongside unwell kidneys that are unable to do so by themselves.

But how do your medical teams estimate how much fluid you must lose for an effective Dialysis session without causing you any harm?

That and the whole clinical effort to help you achieve your Dry Weight is what today’s storytelling is about.

WHY DO KIDNEY FAILURE PATIENTS HAVE EXCESS FLUID RETENTION IN THE BODY?

In patients with kidney failure due to chronic kidney disease, the fluid retention in the body happens because of a number of reasons:

Inability of unwell kidneys to remove excess fluid (water) via urine. This is a direct result of Chronic Kidney Disease damaging delicate kidney filters beyond repair.

Build-up of a water-retaining mineral called Sodium in the blood. In good health, excess Sodium is normally removed from the body via urine. This ability takes a hit with kidney failure. As a result, high excess sodium load in blood causes a fluid overload in the body.

Uncontrolled loss of blood (plasma) protein chiefly Albumin in the urine. Protein loss in urine reduces the overall blood levels of Albumin. This, in-turn, “pulls-out” water from blood and tissues to areas under the skin & causes swelling of dependent areas like the feet & ankles.

Due to Steroid medicines: Some Kidney Patients are on Steroids like Prednisone (Wysolone®, Omnacortil®). These steroids cause water retention within tissues as a side-effect.

 If there is any advanced Heart or Liver disease associated with or in addition to Kidney Failure.

Whatever be the mechanism, Fluid retention within the body quite naturally causes weight gain. This overall increase in body weight due to water retention is technically called “Fluid Weight”.

HOW DOES FLUID RETENTION IMPACT THE BODY?

Fluid retention in the body is dangerous if left unattended. It can excessively strain both your heart and lungs as explained below:

Fluid retention & Heart:

Build-up of excess fluids in the body progressively raises the blood pressure. As a result, the heart needs to put in “greater effort” against such high pressure, to pump out blood to the body. This tires out the heart muscles over time and makes them abnormally thick but sluggish.

Ultimately, all these changes increase the overall heart size, greatly weaken the heart pumping capacity and pave way for “Congestive Heart Failure” (CHF). Like a vicious circle, this further worsens the fluid retention problem.

Fluid retention & Lungs:

A poor pumping capacity of the heart impedes lungs from inflating fully while breathing in. Further, the disease process of CKD can also sometimes lead to fluid collection in the tissue-sacs (called pleura) that normally hold our lungs in place. Such fluid presses inwards on the lungs.

As a result, patients experience a constant “out-of-breath” sensation. This makes them take in shallow, rapid breaths frequently. However, this never fully meets the overall Oxygen requirement of the body and the incessant breathlessness stays.

These are precisely the complications that can be avoided or even greatly delayed with blood-pressure reducing medication and later with excess fluid removal with the added help of Dialysis till a matched donor kidney becomes available for transplantation.

While BP meds remove excess water by purging-out the excess load of water-attracting minerals like Sodium via urine, Dialysis machines can be “pre-set” to control the quantity of fluid removal from the body, by tweaking the Dialysate fluid.

Fine. But how do you know how much fluid to remove via Dialysis?

This is exactly where the concept of “Dry Weight” chips in.

DRY WEIGHT

Your normal body weight at which you don’t have any fluid retention in the body and are at normal blood pressure (130/85 mm Hg) is called Dry weight.

The purpose of Dialysis is to restore your body weight to as close to your “Dry Weight” as possible, by removing all excess fluid accumulated within the body.

Because multiple factors can variably contribute to fluid retention in the body during kidney failure, the quantity of fluid that needs to be removed to achieve your dry weight can differ in each session.

Similarly, not all weight gain during the time between dialysis is due to fluid retention. Some of it could also come from non-fluid sources like increase in fat content as a side effect of taking steroid medicines. Dialysis only reduces fluid weight. Other forms of weight gain such as the part coming from increase in fat tissue cannot be reversed with Dialysis. This means your “Target Dry Weight” can also change with each session.

Therefore, it requires precise assessments to find out what part of your weight gain comes from fluid retention. This is necessary to prevent unintentional loss of excess fluids from the body during the Dialysis session.

Always make it a point to report to the nursing staff if you get any dizziness or muscle cramps during the Dialysis session. This most often happens when fluid is removed too rapidly, or fluid is removed in quantities more than necessary. There is a limit to how much fluid can be safely removed from the body per dialysis session as well.

It is because of these factors that in the initial days of starting haemodialysis, a number of sessions could be necessary to get an accurate idea of your true Dry Weight and the approximate pattern with which it varies between Dialysis sessions.

Calculating your “Target Dry Weight”

1. Why is this crucial?

As pointed out in the section above, it is not necessary that all of the weight gained in between Dialysis sessions would be Fluid weight. It could come from non-fluid sources like increase in fat content due to steroids as well.

Since Dialysis is meant to only remove excess fluid and blood wastes, it is necessary to correctly estimate the portion of weight gain that comes from fluids. Else the patient would end up losing more fluid than they should, which is not good for the patient.

Let us explain with an example:

Your Dry weight is calculated in Kilograms (Kg). Conversion: 1 kg = 2.25 pounds

Say a patient weighs 60 kilograms at Dry weight immediately after a Dialysis Session. There is usually a gap of 2-3 days until the next session.
If this patient presents with 62 kilograms in the next session, the total weight gain would be 2 kilograms.

Now it is not necessary that the entire 2 kg weight gain is due to fluid retention. It could very well be, say, 1.5 kg from fluid retention and 500 mg due to increase in non-fluid weight like fat or even constipation!

In such a scenario, if the medical team erroneously estimates the entire 2 kg as fluid gain and sets the Dialysis machine accordingly, the patient stands the risk of losing more fluid than they should. This will dehydrate the patient, they will present with sudden dizziness, extreme tiredness and/or muscle cramps.

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2. Estimating your Target Dry Weight in the clinic

A. DIFFERENCE IN BODY WEIGHT

Taking body weight measurements right after a Dialysis session and before the next Dialysis session helps gives a rough idea of the weight of excess fluid that may have accumulated in between Dialysis sessions.

Remember. While measuring your Body weight ALWAYS CHOOSE:

The same weighing machines

Different weighing machines can have variable calibrations that could cause errors in your weight recording.

Similar clothing

This is noteworthy. Say one day you measure yourself wearing heavy denims and the other day, a summery linen attire. The difference in the weight of your clothes would quite naturally confound your true weight gain. Stick to clothes of similar weight at the time of measuring your body weight.

Wondering what to do in Winters? Go for layered clothing!

Uniform nutritional status & time of the day

Whatever we eat or drink or purge immediately shows up in our body weight. If you usually go for morning Dialysis Sessions right after a light breakfast and normal bowel habit, sudden change in the session timing, say after a heavy lunch or an interruption in your usual bowel habit would again mask the true weight gain.

As far as possible, stick to measuring your body weight at the same time of the day, with similar food & bowel routine for correct weight recording.

However, as explained above, all of the increase in weight might not be fluid alone. So, your medical teams have to rely on a combination of some “clinical signs” & Medical Tests to decide on how much fluid you must lose to achieve your ideal Dry Weight.

B. CLINICAL SIGNS

Clinical signs that indicate you are at your ideal Dry Weight include the following:

Raised blood pressure gets back to normal range (below 130/85 mm Hg) after Dialysis session & remains below 140/90 until the next Dialysis session without the use of BP lowering meds.

You start breathing with relative ease. (non-specific)

The fluid swelling in your hands, feet, face (especially under the eyes) subsides. (non-specific)

You do not feel dizzy, experience fatigue or get any muscle cramps during or after the Dialysis session. This happens when you lose fluid way too fast or more than you should. (non-specific)

C. MEDICAL TESTS

Medical Tests that help assess your body fluid status are as below:

Your Chest X-Ray (PA View) shows a normal Heart width to Lung Width ratio.

i. Technical name for such ratio of maximal Heart Width to maximal Lung Width is Cardio-Thoracic Index or CTI

ii. A CTI of less than 0.48 co-relates fairly accurately with your Dry Weight. Here CTI of 0.48 would basically mean heart not wider than half the width of lungs.

Blood & Urine test to find levels of “Natri-uretic” peptides.

i. Natri-uretic peptides are small blood protein fragments associated with removing Sodium via urine.

Imaging study to check the width of one of your main Veins called Inferior Vena Cava (IVC) that ferries all blood back to your heart.

i. Greater the width, more fluid-laden blood this vein is having to handle, hence greater the fluid retention

Continuous Blood Volume monitoring during Dialysis

i. Haemodialysis machines allow for this functionality.

Bio-impedance Analysis

i. Non-invasive method to measure body composition – Total body water, body fat content, lean tissue mass etc.

ii. One of the potential uses is the ability to deduct body fat content from total body weight to get approximate fluid weight.

iii. Not recommended for extremely sick patients with life expectancy not more than 1 year or those with metal implants like pacemakers or patients who have had major amputations

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Tips to maintain your Dry Weight in between your Dialysis Sessions

Monitor your overall fluid intake

When we say fluids, we mean all liquids (soups, milk, juice, smoothies etc.), and not just water intake.

Most dialysis patients are advised to restrict their daily fluid intake to 32 Ounces (2 litres)

There is a limit to how much fluid can be safely removed per Dialysis session without causing  you any side effects. So, dialysis patients should take care to NOT gain more than 1 kg (2.25 lbs) weight in one day during the time between Dialysis sessions. This is equivalent to 2-3 kg weight gain due to fluid in between Dialysis sessions. Any more fluid gain would prevent removing all of the fluid in the next Dialysis session. This fluid retention will continue to add up and only worsen the clinical outcome.

Follow a kidney-friendly diet plan

A Renal Diet Plan allows you to effectively combat blood Sodium overload and increase efficiency of Dialysis treatments.

Keep track of your daily weight

This is important. Make it a point to stick to these guidelines as outlined before, to ensure correct weight measurement.

Report any abrupt weight gain or weight loss to your medical team immediately.

Take all your medication correctly and on time

All CKD patients are on a slew of medication. These can range from those that help to maintain your blood pressure & reduce protein loss in urine to those for anaemia, high blood acidity and bone mineral disorders. There could also be medicines for the root condition that caused kidney disease in the first place, like medicines to control blood glucose levels in Diabetics. The list is not exhaustive.

All these medicines  assist your unwell kidneys to stay put for longer, much like scaffolding of a tent.

(As a side note, imagine all the activities that your humble kidneys take care of, in good health!)

Taking these medicines as prescribed delay the progression of kidney damage and improve your longevity on Dialysis.

REFERENCES:

1. National Kidney Foundation Resources https://www.kidney.org/atoz/content/dry-weight

2. GunaI I Ali | How to Determine ‘Dry Weight’ | Kidney Intl Suppl (2011), 2013 Dec; 3(4):377-379. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4089573/

3. Furuland H., Stenberg H., Henriksson C. et al | Perspectives on clinical use of bioimpedance in haemodialysis: Focus group interviews with renal care professionals | BMC Nephrol 19, 121 (2018). https://doi.org/10.1186/s12882-018-0907-4