What to know about kidney failure and dehydration

How does dehydration affect the kidneys?

People are continuously losing water through their skin, lungs, kidneys, and gastrointestinal (GI) tract. When the loss of water is higher than the gain, receptors in the brain begin to detect a lack of water in the blood and release antidiuretic hormone. This prompts the kidneys to reabsorb more water.

As blood pressure decreases, this triggers the kidneys to release renin, which is an enzyme. Renin converts a hormone called angiotensin 1 to angiotensin 2. As the level of angiotensin 2 increases, the adrenal glands release aldosterone, another hormone. Aldosterone further increases the reabsorption of water and sodium in the kidneys.

Dehydration can play a role in the development of UTIs and kidney stones.

When a person is severely dehydrated, they may develop AKI, which is when the kidneys can suddenly decline in function. This means that waste products can build up in the blood as the kidneys are not filtering them out of the body as effectively as usual.

AKI does not always cause symptoms, but some signs of the condition include:

• producing less urine than usual or none at all
• nausea
• fatigue
• swelling in the legs, ankles, or feet
• flank pain
• high blood pressure
• shortness of breath
• chest pain
• confusion or mood changes
• loss of appetite
• seizures or coma, in severe cases

A person needs to seek medical attention if they think they may be experiencing AKI.

Causes of dehydration

Older adults, in particular, are more likely to experience dehydration because they often have underlying health conditions. Some examples include diabetes, kidney disease, and problems with mobility.

People with access to water rarely become severely dehydrated. Instead, dehydration is usually a complication of an illness. For example, a person with diabetes may experience dehydration when their blood sugar levels are very high.

Severe dehydration reduces kidney function, and causes include:

• Inability to replace water loss: This may result from difficulties with mobility, thirst regulation dysfunction, cognitive decline (reduced thinking ability), or loss of consciousness from a drug overdose.
• Water loss from the skin: This can occur due to heat, excessive exercise, burns, or skin disease, for example.
• Water loss from kidneys: This can result from diuretic use, acute or chronic kidney disease, and hyperglycemia.
• Water loss from the GI tract: This may result from vomiting, diarrhea, or taking laxatives.
• Water loss through the abdomen: This can occur due to pancreatitis, ascites, or peritonitis, for example.
• Other water loss: This can occur through sepsis, side effects of certain medications, hyperthyroidism, and chronic obstructive pulmonary disease.

A person needs to speak with a healthcare professional about how to treat and manage any underlying health conditions to help prevent dehydration.

Fluid intake and kidney failure

There are two types of kidney failure: AKI and chronic kidney disease. AKI refers to a sudden loss of kidney function, while kidney failure due to chronic kidney disease results from a gradual loss of kidney function.

Healthcare professionals may advise that individuals with kidney failure from chronic kidney disease reduce their fluid intake. Before making any changes to their fluid intake, a person needs to discuss this with their doctor.

If a doctor thinks a person is experiencing AKI, they may recommend the person undergo a fluid challenge. The purpose of the fluid challenge is to monitor fluid intake and urine output.

If a person’s kidneys improve when they drink more fluid, they likely have prerenal AKI, which tends to occur when there is reduced blood flow to the kidney. This can occur in any individual.

When a person retains fluid during the challenge or experiences fluid overload, they will likely need diuretics, and a doctor will need to monitor their potassium, phosphorus, and sodium intake. However, diuretics may worsen AKI in some cases.

Tips for maintaining kidney health

There are plenty of ways a person can help maintain optimal kidney health, including:

• keeping blood pressure below 140/90 millimeters of mercury or the target the doctor has set
• staying in a healthy blood sugar range
• getting or staying physically active
• engaging in a kidney-friendly diet, which may involve eating more fruits and vegetables and less salt
• taking any medications as a doctor instructs
• quitting smoking, if applicable

Summary

When a person has severe dehydration, it can contribute to acute kidney injury (AKI), which is a type of kidney failure.

Dehydration increases the amount of metabolic waste in the body, as the kidneys can no longer flush this waste out as well as they used to. Furthermore, the more dehydrated a person is, the more the brain stimulates the kidneys to retain more water and sodium.

Eventually, this breakdown in processes can cause AKI. When this happens, the kidney cannot properly filter out waste from the blood, which can be fatal if a person does not receive prompt treatment.

Because people are always losing water through their skin and other organs, they need to ensure they stay hydrated. However, those with kidney failure due to chronic kidney disease may need to limit their fluid intake, depending on a doctor’s guidance.