How Target Weight and Fluid Gain Affect Dialysis Patients

A person with healthy kidneys may urinate up to seven times a day. Most people on dialysis, however, make little to no urine, because their kidneys are no longer properly removing wastes and extra fluid from the body. Without urination, fluid builds up in the body and can cause swelling, shortness of breath and/or weight gain. Hemodialysis filters the blood to remove excess fluid from your blood to get you down to your target weight, also called "dry weight."

What is target weight?

Target weight is your weight without the excess fluid that builds up between dialysis treatments. This weight is similar to what a person with normal kidney function would weigh after urinating. It is the lowest weight you can safely reach after dialysis without developing symptoms of low blood pressure such as cramping, which can occur when too much fluid is removed.

Dialysis cannot rid the body of fluid as effectively as healthy kidneys that work around the clock. Most hemodialysis patients go to dialysis treatment three times a week for about four hours, so the body holds onto extra fluid and waste in the days between treatments.

Fluid is removed during dialysis to return the patient to their target weight by the end of the treatment. Ideally, the goal is to target a weight where the patient will be normally hydrated (not feel thirsty) and feel comfortable.

How is target weight determined?

In most cases, target weight is an estimate determined by your doctor, based on their experience and your input. Your doctor will prescribe your target weight based on your weight when you have:

• Normal blood pressure
• The absence of edema or swelling
• Neck veins that are not distended
• The absence of lung sounds (rales and crackles) related to fluid overload
• No shortness of breath or congestive heart failure
• A normal size heart shadow on X-ray

It is generally a clinical estimate since there are no reliable scientific ways of measuring target weight. Many patients can be above their target weight and have extra fluid without it being noticeable or causing clinical symptoms.

Target weight should be assessed every three to six weeks and adjusted when a patient gains or loses actual weight. Other factors, such as urine output and swelling between treatments, also should be considered when adjusting the target weight. (Urine output often stops completely after six months of being on hemodialysis.) Your doctor will determine target weight gain, as opposed to fluid weight gain.

What You Need to Know About Fluid Gain

Fluid gain is caused by a decrease in urine flow and a normal to increased intake of dietary fluids. Fluid gain is determined by your weight gain between treatments, which is why you are weighed before each dialysis treatment begins. Fluid gains between dialysis treatments should not be more than 5% of estimated target weight.

If too much fluid accumulates between dialysis treatments, it is more difficult to get down to the target weight. A gain of less than 5% of a patient’s body weight is easier to remove than gains above 5%, which may be harder to remove and may cause the patient to have an uncomfortable dialysis treatment.

What happens if you go below target weight?

Your health care team at the dialysis center will monitor your treatment to help you have a complete and comfortable treatment. If too much fluid is removed and a person goes below their target weight, a patient may experience dehydration causing:

• Thirst
• Dry mouth
• Lightheadedness that goes away when laying down
• Cramping
• Nausea
• Restlessness
• Cold extremities
• Rapid heartbeat

If you gained actual weight and your target weight was not raised accordingly, too much fluid may be removed during dialysis. Tell your health care team if you believe your target weight has changed or if you are experiencing any discomfort during your dialysis treatment.

How Fluid Gain Affects Dialysis

Excess fluid affects the body in harmful ways. It can cause:

• Weight gain
• Increase in blood pressure due to extra fluid in the blood stream
• Swelling, called edema, in the feet, ankles, wrists, face and around the eyes
• Abdominal bloating
• Shortness of breath due to fluid in the lungs
• Heart problems, which can include a fast pulse, weakened heart muscles and an enlarged heart

If you exceed your recommended fluid allowance between treatments, more fluid must be removed. There is a limit, however, on how much fluid can be safely removed during a dialysis treatment.

Removing excessive fluid gain can make treatment uncomfortable. Patients can experience a sudden drop in blood pressure, which usually occurs toward the end of a dialysis treatment. You may feel nauseated, weak and tired because your body may not be used to having so much fluid removed at once. Some people experience muscle cramping during dialysis when they gain too much fluid weight. Taking out a lot of fluid at one treatment can also leave you feeling dizzy or weak after the treatment. Not removing enough fluid; however, may leave the patient overloaded, put added strain on the heart, keep the blood pressure high and cause difficulty for the next treatment. One of the most common reasons for a patient on hemodialysis to go to the hospital is for fluid overload that causes shortness of breath. Sometimes, an extra dialysis treatment may be required to remove all the extra fluid.

Long-term Effects of Fluid Gain for Dialysis Patients

Large fluid gains between hemodialysis treatments can be hard on a person's heart and lungs. Short-term effects of fluid overload include cramps at dialysis, headaches and breathing difficulties, and serve as warnings for potential problems in the future. That’s why it’s important to monitor and keep fluid gain in check between dialysis treatments. Your efforts in limiting fluid intake can affect your immediate well-being and your long-term health.

By keeping fluid gains as low as possible between dialysis treatments, you can help minimize the risk of serious health problems. Repeatedly overloading your system with fluid makes your heart work harder and may lead to heart problems.

Limiting Fluid Intake Between Dialysis Treatments 

Restricting your daily fluid intake will help you feel more comfortable before, during and after your dialysis sessions. It also reduces the chances of unpleasant symptoms during dialysis and potential health problems over time.

Each patient has a different allowance for daily fluid depending on physical activity level, body size and urine output. Most people on hemodialysis are limited to approximately 32 to 50 fluid ounces per day, compared to a fluid intake of 100 ounces daily for someone who has working kidneys. Talk to your dietitian if you have questions about how much fluid you can have each day.

Following the Dialysis Diet

Diet is an important part of treatment for dialysis patients. Certain foods must also be counted in your daily fluid intake. In general, anything that is liquid at room temperature is considered a fluid.

These guidelines may help you follow your recommended daily fluid intake between dialysis treatments:

• Avoid salt and salty foods because they can cause thirst and water retention.
• Drink only recommended quantities of water and other beverages.
• Limit foods that contain liquid, or are liquid at room temperature. 
• Measure foods accurately. Use a food scale, measuring spoons and measuring cups for both dry and liquid measures.
• Monitor your daily weight gain on a digital scale.
• Keep a daily food and fluid diary.

The dialysis diet isn’t easy, but your dietitian and other patients can give you tips on how to limit your daily fluid intake and still feel satisfied. For example, when the urge to quench your thirst strikes, suck on a mint, brush your teeth or use a spray bottle to squirt a small amount of water into your mouth for instant relief. Watch this short video on how to manage thirst with a frozen water bottle.

Summary

During each dialysis treatment, fluid is removed to get patients down to their target weight. Fluid gain between dialysis treatments will occur because kidneys are no longer removing fluid from the body; however, people on hemodialysis may feel better and have more comfortable treatments if they don’t gain too much fluid over their target weight between hemodialysis treatments.  

External articles
Dry weight and blood pressure: The Nephron Information Center
Assessment of Dry Weight in Hemodialysis: Journal of the American Society of Nephrology      


This article is for informational purposes only and is not intended to be a substitute for medical advice. Consult your dietitian or physician for the specific diet that is right for you as diet guidelines vary for each individual based on health condition, diagnosis and many other factors.