Hyponatremia

What is Hyponatremia?

Hyponatremia is a condition where the salt (sodium) levels in your blood are lower than normal, specifically less than 135 mEq/L – although this can vary slightly between different lab tests. This is a common issue usually caused by an overabundance of water in the body compared to the amount of sodium.

In simple terms, the level of sodium in your blood isn’t directly dependent on the amount of body sodium but on the relationship between total body elements (like sodium and potassium) and total body water. Hyponatremia happens when there’s an imbalance in this relationship because there’s more water than solutes (substances dissolved in a solution).

Your body’s water (TBW) is primarily split between two areas. One-third is in the extracellular fluid (ECF), which is the fluid outside of your cells; the remaining two-thirds is the intracellular fluid (ICF), which is the fluid inside your cells. Sodium is the main element in the ECF, while potassium is the major one for the ICF.

What Causes Hyponatremia?

Hyponatremia is a condition caused when the sodium levels in your body are too low. What causes hyponatremia can be determined by checking the volume of fluid outside your cells, also known as extracellular fluid (ECF). Sodium is important because it is the main component of this fluid. Depending on the ECF volume, hyponatremia can be categorized into three types: low volume (hypovolemic), normal volume (euvolemic), or high volume (hypervolemic).

Certain conditions can cause hyponatremia. For instance, if too much of a hormone called vasopressin gets released or if you drink lots of liquids, you might end up with this condition. Problems with your thyroid or adrenal gland can also raise your vasopressin levels. Similarly, losing intravascular volume (the fluid inside your blood vessels) can lead to hyponatremia.

If you have hyponatremia with low volume, some causes could be loss of body fluids through vomiting or diarrhea, certain diseases like pancreatitis, use of water pills (diuretics), presence of kidney disorders that make you lose salt, or not having enough of a hormone called mineralocorticoid.

On the other hand, hyponatremia with high volume is usually due to problems with your kidneys, like kidney failure, being related to heart conditions or liver cirrhosis, or it might even be caused due to a treatment/response to a treatment (iatrogenic).

As for hyponatremia with a normal fluid volume, you might have it due to the use of certain medications or if you have a condition called Syndrome of Inappropriate Antidiuretic Hormone (SIADH). Other causes include Addison’s disease, problems with your thyroid, drinking too much liquid, or even undergoing certain medical procedures that require you to drink lots of fluids.

There are numerous drugs that can lead to hyponatremia such as vasopressin analogs (which are similar to vasopressin), drugs that increase the release of vasopressin like some antidepressants and painkillers like morphine, medicines that affect the concentration of your pee such as certain diuretics, and others such as antipsychotics, anti-inflammatory drugs, and even some illicit drugs like ecstasy.

Risk Factors and Frequency for Hyponatremia

Hyponatremia, which is an imbalance of certain chemicals in your body, is quite common. It’s especially prevalent in people who are in the hospital, affecting 20 to 35% of these patients. Critical patients in intensive care units or those who have recently had surgery are more likely to face this issue. This imbalance is often seen in older adults because they tend to have more health problems, take more medications, and might not always have access to proper nutrition.

• Hyponatremia is the most common chemical imbalance in the body.
• 20 to 35% of people in the hospital have this condition.
• It’s common in patients in intensive care units or those who have had surgery.
• Older adults are more likely to have this condition because they often have more health problems, take several medications, and may face challenges in accessing food and drinks.

Signs and Symptoms of Hyponatremia

Hyponatremia is a condition where the level of sodium in the blood is abnormally low. Its symptoms can vary depending on how severe it is and how quickly it develops. People with mild to moderate hyponatremia (sodium level above 120 mEq/L) or a slow decrease in sodium levels over a long period (more than 48 hours) usually have minor symptoms. However, those with severe hyponatremia (sodium level below 120 mEq/L) or a rapid decrease in sodium levels may experience a variety of more severe symptoms.

• Anorexia (loss of appetite)
• Nausea and vomiting
• Fatigue
• Headache
• Muscle cramps
• Altered mental status
• Agitation
• Seizures
• Coma

Beyond the symptoms, doctors also look into the patient’s medical history, home medications, and lifestyle habits such as whether they have previous lung and brain disorders, if they consume lots of beer or use certain drugs like MDMA or ecstasy. A physical check-up is done to assess the patient’s body fluid level and neurological status. If neurological symptoms are found, treatment needs to be started quickly to prevent lasting damage to the nervous system.

Testing for Hyponatremia

If your doctor suspects you have low sodium levels, also known as hyponatremia, there are several steps they will follow:

Step 1: Plasma Osmolality Test (275 mOsm to 290 mOsm/kg)

Plasma osmolality refers to the concentration of substances in your blood. This test can help your doctor determine the type of hyponatremia you might have: hypertonic, isotonic, or hypotonic. Patients with true hyponatremia are hypotonic, meaning their blood is less concentrated. If this is the case, your doctor will move on to step 2.

Step 2: Urine Osmolality Test

This test checks the concentration of particles in your urine. If it’s less than 100 mOsm/kg, it could be a sign of primary polydipsia or reset osmostat, both conditions related to fluid balance in your body. If the concentration is more than 100 mOsm/kg, it usually means you have a high level of ADH, a hormone that regulates water in your body. In this scenario, your doctor will proceed to step 3.

Step 3: Volume Status Evaluation (ECF status)

ECF is short for extracellular fluid – the fluids outside the cells in your body. Your doctor will examine this to understand whether you’re experiencing low fluid volume (hypovolemic), normal fluid volume (euvolemic), or high fluid volume (hypervolemic). If your fluid volume turns out to be low, your doctor will proceed to step 4.

Step 4: Urine Sodium Concentration Test

This test measures the amount of sodium in your urine. If it’s less than 10 mmol/L, it suggests you’re losing fluid from somewhere outside your kidneys, which could be due to past use of diuretics or previous episodes of vomiting. If it’s more than 20 mmol/L, it suggests your kidneys are losing too much urine. This could be due to several reasons such as using diuretics, vomiting, having a cortisol deficiency, or certain kidney disorders that lead to excessive loss of salt.

Your doctor may also perform other tests to pinpoint the cause of your hyponatremia including:

– Serum thyroid-stimulating hormone (TSH) test
– Serum adrenocorticotropic hormone (ACTH) test
– Serum urea test
– Liver function tests
– Chest X-ray or a special imaging test called a computed tomography (CT) scan of the chest
– CT scan of the head

All these tests will help your doctor to understand your condition better and plan your treatment accordingly.

Treatment Options for Hyponatremia

The treatment for hyponatremia, a condition characterized by low sodium levels in the blood, varies. It can depend on factors like how severe the condition is, how long the person has had it, if they’re displaying symptoms, and their volume status (the amount of blood and fluids in their body).

There are different treatment plans for acute symptomatic hyponatremia (when the condition has recently developed and is causing noticeable symptoms) and chronic asymptomatic hyponatremia (when the condition has been present for a longer period and isn’t causing noticeable symptoms).

In case of severe symptoms due to acute hyponatremia, doctors may administer a strong saline (salt) solution intravenously. For mild to moderate symptoms, a slower saline infusion might be given. The rate of this infusion could be adjusted based on regular checks of sodium levels.

Chronic asymptomatic hyponatremia treatment plans differ based on the volume status. If the patient has less than normal volume of blood and fluids (hypovolemic), they might be given isotonic fluids (fluids balanced with the concentration of salts and sugars in a person’s body), and their use of any diuretics (medications that help the body remove sodium and water) might be stopped. If there’s a larger volume of fluids than normal (hypervolemic), the underlying condition causing it might be treated. A person may be asked to restrict salt and fluids and may be given diuretics to remove excess fluid. If the volume status is normal (euvolemic), the patient might be advised to limit their fluid intake to less than 1 liter per day.

Newer medications that increase the excretion of water in kidneys without affecting sodium have been used for treating hyponatremia. These are typically used for patients with normal or larger than normal fluid volumes, except in the cases of liver failure.

The goal in treating hyponatremia is to increase sodium levels in blood carefully, ensuring it doesn’t increase more than 10 to 12 milliequivalents per liter (mEq/L) in a day. It’s important to control the rate of sodium increase to avoid a condition called osmotic demyelination syndrome (ODS), a rare but serious condition that can cause nerve damage. Risks of ODS are higher in people with low potassium levels, liver disease, malnutrition, and those who drink alcohol.

In rare cases, patients may have severe, chronic hyponatremia. They might be given a saline solution intravenously at a slow rate alongside medications to prevent the sodium levels from rising too quickly. In certain cases, tolvaptan, a medication indicated for hyponatremia associated with high anti-diuretic hormone (ADH) activity is used.

Patients with normovolemic hyponatremia (normal fluid volume but reduced sodium concentration) usually only need to limit their water intake. For those with SIADH (a disorder that leads to water retention and diluted sodium concentration), in addition to fluid restriction, high protein intake might be needed. This increases the solute load, leading to the removal of more free water from the body. Serum sodium levels and osmolality (concentration of all chemical particles found in the fluid part of blood) would both be low, while urinary sodium levels and osmolality would be high in these patients.

What else can Hyponatremia be?

True hyponatremia refers to low sodium levels in the blood and is linked with lowered osmolality, or less concentration of substances in your bodily fluids. It is important to first distinguish it from conditions that cause a high-concentration (hyperosmolar) and same-concentration (iso-osmolar) type of hyponatremia, also known as pseudo-hyponatremia.

Some conditions that can lead to high-concentration (hyperosmolar) hyponatremia are:

• High blood sugar levels (Hyperglycemia)
• Overdosing on a drug called Mannitol
• High levels of fats in the blood (Hyperlipidemia)
• High protein levels in the blood (Hyperproteinemia)

On the other hand, several conditions could cause low-concentration (hyposmolar) hyponatremia. Here are some examples:

• Stomach flu (Gastroenteritis)
• The use of certain drugs that increase urination (Diuretics)
• Heart’s inability to pump enough blood effectively (Congestive heart failure)
• Liver failure
• Drinking excessive amounts of water (Psychogenic polydipsia)
• Kidney problems (Renal causes)
• A condition that makes your body produce too much antidiuretic hormone (SIADH)
• Severe adrenal gland failure (Adrenal crisis)
• Underactive thyroid (Hypothyroidism)

What to expect with Hyponatremia

The outlook for patients with hyponatremia, or low sodium levels in the blood, largely depends on how severe the condition is and what’s causing it. The prognosis may be unfavorable for patients with severe hyponatremia, sudden onset of the condition, and for older individuals.

Possible Complications When Diagnosed with Hyponatremia

Hyponatremia, a medical term for low sodium in the blood, can have serious side effects if not sufficiently treated. Some of the alarming consequences include muscle breakdown (rhabdomyolysis), changes in mental state, seizures, and even falling into a coma.

Correcting chronic hyponatremia too quickly (raising sodium levels by more than 10 mEq/L to 12 mEq/L within a day) can result in a harmful condition called osmotic demyelination syndrome.

Osmotic demyelination syndrome, formerly known as central pontine myelinolysis, is a dangerous complication that arises from speedily increasing sodium in the blood in patients with longstanding low sodium levels. When a person has hyponatremia, their brain adjusts to function with low sodium levels in about two days, meaning they may not show symptoms even if their sodium levels are seriously low. However, if sodium levels rise too swiftly after the brain has adapted to the low sodium state, it can lead to osmotic demyelination syndrome.

The symptoms of this syndrome often occur a few days after the sodium correction and include permanent neurological effects such as seizures, confusion, and even a coma. In worst-case scenarios, patients can develop “locked-in” syndrome, where they are conscious but incapable of moving, communicating only by moving their eyes.

Please understand these complications:

• Untreated hyponatremia leading to muscle breakdown
• Altered mental state
• Seizures
• Coma
• Osmotic demyelination syndrome from rapid correction of chronic hyponatremia
• Severe neurological symptoms post rapid sodium correction
• “Locked-in” syndrome in severely affected patients

Preventing Hyponatremia

Patients suffering from hyponatremia, or low sodium levels in the blood, should receive regular monitoring after hospital discharge. This monitoring should involve both their usual healthcare provider and a kidney specialist. They may also need further laboratory tests as determined by their doctors, depending on their condition. If the doctors advise these patients to limit their fluid intake, they should be provided with the correct information and guidance to understand and follow it properly.