Low blood sodium, or hyponatremia, is a common effect of heart failure. This can lead to worse outcomes while receiving heart failure treatment.
Hyponatremia refers to low sodium levels, a crucial electrolyte, in the blood. Sodium is crucial for blood pressure control, nerve and muscle function, and fluid balance. Various bodily changes can impact sodium levels, including health conditions that change fluid levels.
Heart failure is one of these conditions. It occurs when the heart can no longer pump enough blood to keep the body working as it should, usually due to the heart muscles becoming too weak or stiff over time. One of heart failure’s symptoms is fluid buildup in the body, which can alter sodium levels.
Hyponatremia is the most common issue with electrolytes in people who have heart failure. Doctors define hyponatremia as a blood sodium measurement under
According to a 2023 review, around 20% of all people in the hospital for heart failure have hyponatremia. Low blood sodium tends to persist throughout their hospital stay.
Most crucially, the review suggests that hyponatremia has a strong correlation with worse outcomes for people with heart failure. However, it is unclear whether the hyponatremia causes the poor outlook or happens to occur alongside it, as well as if it is an adverse effect of taking loop diuretic medications to manage fluid retention.
Low sodium levels can develop
The main causes of hyponatremia include:
- Hypervolemic hyponatremia: This type occurs when the body has an excess of fluids and sodium, but the increase in fluids is significantly greater than the increase in sodium levels. This is the type with close links to heart failure, as well as kidney failure or scarring of the liver, known as cirrhosis.
- Euvolemic hyponatremia: In euvolemic hyponatremia, fluid levels slightly increase while sodium levels remain roughly the same, which reduces sodium.
- Hypovolemic hyponatremia: In people with this type, the body loses both fluids and sodium during dehydration. However, the body loses more sodium in proportion to the fluids. This might occur due to gastrointestinal fluid loss causes, such as vomiting or diarrhea, or as a side effect of diuretic pills.
Heart failure can lead to hypervolemic hyponatremia as the heart does not pump enough blood around the body. In response, the systems that usually detect fluid and blood pressure interpret this as indicating that the body does not have enough fluids.
This can trigger the release of several hormones, including vasopressin, which instructs the kidneys to hold onto more water. This then dilutes the sodium in the blood.
The presence of symptoms depends on how rapidly sodium levels decrease and the amount by which they decrease.
Mild to moderate hyponatremia
If sodium levels decrease over more than 48 hours or the hyponatremia is mild, people with low blood sodium levels may show no or very few symptoms. If symptoms are present, they may include:
Severe acute hyponatremia
A significant and rapid drop in blood sodium levels can lead to a group of more severe symptoms, known as hyponatremic encephalopathy. These result from fluid buildup on the brain as it loses its ability to control its fluid volume.
Symptoms requiring urgent treatment include:
- vomiting
- seizures
- confusion
- coma
Heart failure symptoms
These may occur alongside
- breathlessness
- leg swelling
- persistent coughing
- wheezing
- fatigue
- appetite loss
- nausea
- a rapid heart rate
- weight changes
A doctor can identify hyponatremia in people with heart failure by using blood tests.
A healthcare professional must identify these causes before trying to correct sodium levels. They will then ask about a person’s medical history, such as diuretic use or a low-sodium diet, as well as check for signs of fluid buildup, including swollen legs or a swollen neck vein. This can help them identify dilutional, or hypervolemic hyponatremia.
Dehydration may suggest that the hyponatremia is depletional rather than dilutional.
Urine testing will also occur to detect the level of sodium the body expels in the urine. In people with dilutional hyponatremia, the body retains excess fluid, resulting in highly concentrated urine. Depletional hyponatremia means the body tries to conserve as much water as possible, resulting in dilute urine.
Generally, treatment for heart failure associated hyponatremia will involve fluid restriction (to less than 800 to 1,000 milliliters (mL) per day), diuretics to remove excess fluids, as well as medications for heart failure. In some cases, vasopressin antagonists, known as vaptans, may be necessary for persistently low sodium levels. In severe cases, a saline drip with medications and continuous monitoring may be necessary.
Medications
Certain medications can interact with the heart and the kidneys to help restore normal sodium levels in people with dilutional hyponatremia. These include:
- Loop diuretics: These medications trigger the kidneys to excrete more water. For individuals with dilutional hyponatremia, such as those with heart failure, this helps rebalance fluid and sodium levels in the body to a healthy proportion. However, the initial dose should be intravenous to speed up the individual’s response to the drugs.
- Vaptans: These block the action of vasopressin, preventing the kidneys from retaining excessive water and allowing the body to eliminate fluids without losing electrolytes. However, doctors only recommend them for short-term use, as their long-term effects are uncertain.
- Inotropes and vasodilators: These can improve the heart’s pumping function, reducing pressure on the heart and improving blood flow to the kidneys. This can help treat hyponatremia and improve outlook in people with heart failure that reduces the heart’s output.
Saline solution
In severe cases, a person may require a saline drip. The medical team will begin by increasing blood sodium levels with a saline drip, typically at a rate of around 5 mEq/L. They will check levels after twenty minutes, and if they note a significant increase in sodium levels and improvement in symptoms, they will stop the drip.
The overall increase should not be more than 10 mEq/L in the first 24 hours and 8 mEq/L every 24 hours after that until sodium levels return to 130 mEq/L. If symptoms continue, the healthcare team may continue the drip.
Several methods can reduce a person’s risk of developing hyponatremia if they have heart failure, including:
- care when using diuretic medications, and following medical guidance closely
- following a doctor’s instruction on diuretic use
- asking a doctor about how many electrolytes a person with heart failure needs to maintain a cautious balance
- following a doctor’s advice on sodium and fluid intake
Hyponatremia, or low levels of sodium in the blood, is fairly common in people experiencing heart failure.
Alongside usual heart failure symptoms, such as breathlessness and fluid buildup, people with mild-to-moderate hyponatremia may experience fatigue, nausea, dizziness, headaches, cramps, and balance or coordination issues. Severe hyponatremia may lead to vomiting, seizures, confusion, and coma.
In heart failure, hyponatremia is typically dilutional (hypervolemic hyponatrmia) and requires treatment with diuretics, fluid restriction, and other medications. In cases that occur due to depletion (hypovolemic hyponatremia), intravenous saline infusions may be necessary.