Dialysis, a life-sustaining treatment for individuals with kidney failure, filters waste and excess fluid from the blood. Since the process is intermittent, fluid builds up significantly between sessions. Therefore, a strict fluid restriction is a necessary component of treatment for nearly all patients with little to no residual kidney function. This restriction prevents serious medical complications and maintains overall health.
How Healthy Kidneys Manage Fluid
The kidneys of a healthy person function as the body’s primary regulators, continuously filtering the entire blood volume to maintain a precise balance of water and electrolytes. They achieve this by adjusting the amount of water and salt excreted in the urine. If a person drinks a large volume of liquid, the kidneys produce a large volume of dilute urine to eliminate the excess. Conversely, if the body is dehydrated, the kidneys conserve water by producing a small amount of highly concentrated urine.
This intricate process is controlled by hormones like vasopressin, which signals the kidneys to reabsorb water back into the bloodstream. When kidney function fails, this automatic control over fluid output is lost, and the body can no longer excrete fluid efficiently.
The Health Risks of Excess Fluid
Without the ability to excrete water, any extra fluid consumed accumulates in the body, leading to a state called fluid overload or hypervolemia. This condition is measured by the weight gained between dialysis sessions, known as interdialytic weight gain. Excessive fluid accumulation places a major strain on the cardiovascular system, which is the leading cause of death in dialysis patients.
The added volume of fluid increases the total blood volume, forcing the heart to work harder to pump the extra load, which can result in high blood pressure, or hypertension. Over time, this sustained effort can lead to the enlargement and weakening of the heart muscle, contributing to the development of heart failure. Research shows that chronic fluid overload increases the risk of mortality, even when blood pressure appears to be controlled.
Fluid can also leak out of the blood vessels and into surrounding tissues, causing swelling known as edema, often noticeable in the feet, ankles, and hands. A more dangerous complication occurs when the fluid collects in the lungs, a condition called pulmonary edema. This causes severe shortness of breath and makes breathing difficult, especially when lying down, because the fluid impairs the lungs’ ability to exchange oxygen.
A high interdialytic weight gain complicates the dialysis session because the fluid must be removed rapidly. Removing fluid too quickly is associated with a higher risk of complications during treatment, including cramping and dangerously low blood pressure. This rapid removal causes significant stress on the heart and is linked to increased cardiovascular morbidity.
Practical Strategies for Limiting Fluid
The goal of fluid restriction is to keep the body at its “dry weight,” which is the patient’s weight without any excess fluid. The daily fluid allowance is specifically calculated by the care team, usually based on a small set amount plus any measurable urine output a patient may still have. Most hemodialysis patients are limited to about 32 to 50 ounces of total fluid per day.
Controlling the intake of sodium is a powerful strategy because salt causes intense thirst and makes the body retain water. Limiting highly processed and salty foods can reduce the drive to drink, making it easier to stick to the fluid allowance. Patients should also be aware of “hidden fluids” that count toward the daily limit, such as soups, gravy, ice cream, and gelatin, which are liquid at room temperature.
To manage the persistent feeling of thirst, patients can use practical techniques that minimize the volume of liquid consumed. Sucking on frozen items, like ice chips or frozen grapes, can be more satisfying than drinking, as they stay in the mouth longer. Using small cups or shot glasses for beverages helps to slow consumption and visually manage the daily allowance.
Sucking on sour candies, sugar-free gums, or lemon wedges can stimulate saliva flow and moisten the mouth without requiring much fluid. Weighing oneself daily is an important monitoring practice. A sudden weight increase is the earliest sign of excess fluid accumulation, allowing for timely adjustments.