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A Comprehensive Guide to Hyponatremia: Understanding, Identifying, and Managing Low Sodium Levels in Patients

Emergency (ER) Fluids & Electrolytes ICU Labs and Diagnostics Med-Surg Medications & Therapies Nephro
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Hyponatremia is the medical term for low levels of sodium in the blood. This is the most common electrolyte disorder seen in the clinical setting, and it can also be pretty confusing to understand overall, since there are multiple different causes for hyponatremia from different physiologic mechanisms. We’ll try our best to simplify it. Sodium plays a vital role in maintaining the body’s fluid balance, nerve function, and muscle contraction. This is why any imbalance can cause major issues. This guide is designed to equip nurses with the knowledge and skills necessary to identify, manage, and monitor hyponatremia effectively in their patients.

Understanding Key Concepts: Osmolality, Diffusion, and Osmosis

Before delving into the specifics of hyponatremia, it’s crucial to understand some fundamental key concepts that underpin our understanding of hyponatremia. These concepts include diffusion, osmolality, and osmosis. Diffusion is a process by which molecules move from an area of higher concentration to an area of lower concentration. This movement continues until there is an equal concentration of molecules in both areas, a state known as equilibrium. In the body, diffusion allows for the transport of substances, such as nutrients and waste products, across cell membranes. Osmosis is a specific type of diffusion that involves the movement of water molecules. Water moves from an area of lower solute concentration (or higher water concentration) to an area of higher solute concentration (or lower water concentration). This movement occurs across a semi-permeable membrane, such as a cell membrane. In the context of hyponatremia, osmosis plays a crucial role. When sodium levels in the blood are low, water tends to move into cells, causing them to swell. This can lead to major symptoms like brain swelling in severe cases. Osmolality is a measure of the total number of solutes in a solution. Sodium, along with other electrolytes and small molecules, contributes to the body’s osmolality. The osmolality will affect osmosis and hydration of cells, so if this is out of whack, complications can arise as above. Also check out: Intravenous Fluids: Types of IV Fluids

Why Is Sodium Important In the Body?

Sodium, a crucial electrolyte in the human body, plays a vital role in several physiological processes. Its importance cannot be overstated, and understanding these roles can help us appreciate the impact of conditions like hyponatremia. Here are some of the key functions of sodium in the body.

a desaturated heart and yellow cardiac conductive tissue showing the SA node, AV node, and ventricles

Fluid Balance

Sodium helps maintain the body’s fluid balance. It attracts water and helps keep fluids in the right compartments within the body. Where sodium goes, water follows. In other words, sodium helps ensure that our cells and tissues have the right amount of fluid to function properly.

A bundle of red blood cells that are clotted together

Blood Pressure Regulation

Sodium plays a role in regulating blood pressure. It affects the blood volume in the blood vessels and the tension of the vessel walls, both of which influence blood pressure levels.

A depiction of a neuron

Nerve Transmission

Sodium is essential for the transmission of nerve impulses. It is involved in the generation and propagation of action potentials, the electrical signals that allow neurons to communicate with each other and with other types of cells. Without sodium, this communication would be severely impaired, affecting everything from muscle contractions to the sensation of touch.

An image of a muscle

Muscle Contraction

Sodium, along with other electrolytes like potassium and calcium, is crucial for muscle contraction. It helps initiate the electrical signals that cause muscles to contract and relax. Without adequate sodium, muscles may not function optimally, leading to weakness or spasms.

A liquid drop with "H+" indicating acid or acidity or hydrogen ions

pH Balance

Sodium contributes to the body’s pH balance. It is involved in mechanisms that help keep the body’s acid-base balance within a narrow range, which is essential for the optimal functioning of the body.

A depiction of the small bowel, which is largely responsible for absorption of magnesium

Nutrient Absorption

Sodium aids in the absorption of certain nutrients in the small intestine. For instance, glucose, an essential source of energy for the body, is often absorbed through a process that involves sodium.

When sodium levels fall too low, all these functions can be disrupted, leading to a range of symptoms and complications. In the following sections, we will explore the causes and symptoms of hyponatremia, as well as how to assess, treat, and monitor this condition.

How is Sodium Regulated in the Body?

Sodium regulation in the body is a complex process involving several organs and hormones. Here’s how the body regulates sodium levels:

A kidney with low fluid levels

The Kidneys

The kidneys play a main role in regulating sodium levels in the body. They filter the blood and selectively reabsorb sodium, allowing the body to retain or excrete sodium as needed. This process is largely controlled by hormones, including aldosterone and antidiuretic hormone (ADH).

An organic chemistry representation of aldosterone the hormone

Aldosterone

Aldosterone is a hormone produced by the adrenal glands. This tells the kidneys to keep more sodium (and water along with it). This process helps increase blood volume and blood pressure.

A generic hormone depiction

Antidiuretic Hormone (ADH)

ADH, also known as vasopressin, is a hormone produced by the pituitary gland. It primarily regulates water balance in the body. When the body is dehydrated, or when blood osmolality is high (indicating a high concentration of solutes like sodium), the production of ADH increases. ADH tells the kidneys to reabsorb more water, diluting the blood and reducing osmolality. This process indirectly affects sodium concentration by altering the amount of water in the bloodstream.

A generic hormone depiction

Atrial Natriuretic Peptide (ANP)

ANP is a hormone produced by the heart (similar to BNP). It is released when the atria of the heart stretch due to increased blood volume. ANP promotes the excretion of sodium by the kidneys, helping to reduce blood volume and blood pressure. This hormone acts as a counterbalance to aldosterone.

A generic hormone depiction

Dietary / Thirst mechanisms

Dietary intake of sodium and the body’s thirst mechanism also play a role in sodium regulation. Consuming sodium in food and drink contributes to the body’s sodium levels. Meanwhile, the thirst mechanism is triggered when the body’s sodium concentration is high, causing the person to drink more. The thirsting mechanism is less effective in elderly patients.

Normal Sodium Levels & Hyponatremia

Normal sodium levels can range from 135 – 145 mEq/L. Anything lower than 135 is considered hyponatremia.

Hyponatremia

  • Normal Levels: 135 – 145 mEq/L
  • Mild Hyponatremia: 130 – 135 mEq/L
  • Moderate Hyponatremia: 120 – 130 mEq/L
  • Severe Hyponatremia: < 120 mEq/L

Acute vs Chronic Hyponatremia

When it comes to treating hyponatremia (discussed below), it’s important to know whether or not this was an acute or chronic change to their sodium level. Acute hyponatremia refers to when sodium levels drop rapidly within 48 hours. This rapid change does not give the body’s cells, particularly brain cells, enough time to adapt to the lower sodium levels. As a result, water moves into cells, causing them to swell. This can lead to severe and potentially life-threatening symptoms, including headache, nausea, vomiting, seizures, respiratory arrest, and brain stem herniation. Treatment of acute hyponatremia more aggressive. Chronic hyponatremia is when sodium levels decrease slowly over a period of more than 48 hours. This slower onset allows the body’s cells time to adapt to the lower sodium levels, reducing the movement of water into cells and the associated swelling. As a result, symptoms of chronic hyponatremia are often milder and can include nausea, headache, confusion, and fatigue. In some cases, chronic hyponatremia may cause no symptoms at all. Treatment of chronic hyponatremia is more cautious.

Causes of Hyponatremia

When talking about hyponatremia, we’re essentially looking at an imbalance in the body’s sodium-to-water ratio. This imbalance can be influenced by various factors that we discussed above. By evaluating serum osmolality alongside sodium levels, healthcare providers can better identify the cause of hyponatremia. This is crucial because the treatment approach for hyponatremia often depends on the underlying cause. For example, hyponatremia due to excessive water intake would be managed differently from hyponatremia due to heart failure or kidney disease. This is why we we will break up possible causes in relation to osmolality here.

Low serum osmolality

Hyponatremia with low serum osmolality is also known as hypotonic hyponatremia. This is the most common type of hyponatremia and occurs when there is an imbalance in the body’s water-to-sodium ratio. It is very helpful to also evaluate hypotonic hyponatremia in regards to fluid status.

A kidney with low levels of water

Hypovolemic (low fluid)

Hypovolemic (low volume) hypotonic hyponatremia occurs when the fluid status is LOW, and the osmolality is also low. This is very common, and usually due to:
  • Dehydration
  • Diuretic Use
  • Addison’s Disease (if also dehydrated)
  • Third spacing of fluids (i.e. with severe burns or pancreatitis)

A kidney with normal fluid levels

Euvolemic (Normal fluid)

Euvolemic hypotonic hyponatremia occurs when the fluid status is normal, but the osmolality is low. This can be from:

  • Syndrome of Inappropriate ADH (SIADH)
  • Severe hypothyroidism
  • Adrenal insufficiency (Addison’s Disease)
  • Medications (i.e. some antidepressants or antipsychotics)
  • Psychogenic polydipsia

What Causes SIADH?

SIADH (produced by the pituitary gland) is when the body produces too much ADH, leading to excessive retention of fluid. Excessive ADH leads to water retention and a dilution of sodium in the blood, resulting in hyponatremia. SIADH can be caused by various conditions, including certain cancers (like lung or brain cancer), lung diseases (like pneumonia or tuberculosis), brain disorders (like meningitis or stroke), and certain medications (like some antidepressants and chemotherapy drugs).

A kidney so full of water that it's bursting

Hypervolemic (HIGH fluid)

Hypervolemic hypotonic hyponatremia is when the patient is HIGH on fluid, with low osmolality.Causes include fluid overload from one of the following:

  • Heart failure (CHF)
  • Kidney Disease (usually end-stage renal disease)
  • Cirrhosis of the liver
  • Nephrotic syndrome

Normal serum osmolality

Hyponatremia with normal serum osmolality is also known as isotonic or normotonic hyponatremia. This is relatively rare. This may be caused by:

A picture of an albumin protein

Hyperproteinemia

Conditions that cause abnormally high protein levels in the blood, such as multiple myeloma, can lead to isotonic hyponatremia. The high protein levels can displace water in the plasma, causing a relative decrease in sodium concentration.

Yellow blobs of cholesterol

Severe Hyperlipidemia

Similarly, conditions that cause high lipid (fat) levels in the blood, such as severe hypertriglyceridemia, can result in isotonic hyponatremia.

High serum osmolality

Hyponatremia with High serum osmolality is also known as hypertonic hyponatremia. This type of hyponatremia is often associated with high blood sugar levels or the presence of other osmotically active substances. Here are some causes:

A glucometer which reads "HIGH" indicating hyperglycemia

Hyperglycemia

High blood sugar levels can lead to hypertonic hyponatremia. The high glucose concentration in the blood draws water out of cells and into the bloodstream, diluting the sodium in the plasma. The body typically pees out this excess fluid, and that is why uncontrolled diabetes often leads to dehydration – a process called osmotic diuresis. With co-existing dehydration, the osmolality may become normal or even low.

An image of the thyroid and parathyroid glands

Mannitol

Mannitol, a type of sugar alcohol used as a diuretic and in the treatment of certain brain conditions (like for increased ICP), can increase serum osmolality and lead to hypertonic hyponatremia.

Nursing Assessment Of Hyponatremia

Symptoms

The symptoms of hyponatremia can vary widely depending on the severity of the condition, how quickly it develops, and the individual’s overall health status. Here are some common symptoms:

A battery symbol which is low

FATIGUE

Low sodium levels can interfere with the body’s energy production processes, leading to feelings of fatigue or lethargy.

Lips with blue tingling numbness around it

HEADACHE

A headache is often one of the earliest symptoms of hyponatremia.

A muscle with red electric bolts indicating pain

NAUSEA AND VOMITING

Hyponatremia can affect the functioning of the gastrointestinal tract, leading to feelings of nausea and, in more severe cases, vomiting. This can further exacerbate hyponatremia if the vomiting leads to a loss of sodium and water.

A muscle with red electric bolts indicating pain

MUSCLE WEAKNESS AND CRAMPS

Sodium plays a crucial role in muscle contraction. When sodium levels are low, individuals may experience muscle weakness, cramps, or spasms.

graphic of a brain

ALTERED MENTAL STATUS

As hyponatremia progresses, it can affect brain function, leading to symptoms such as confusion, disorientation, and difficulty concentrating. Extremely low sodium levels can cause a loss of consciousness or coma due to the severe swelling of brain cells.

A blue brain with yellow lightning bolts depicting a seizure

SEIZURES

In severe cases of hyponatremia, the rapid swelling of brain cells can lead to seizures.

Fall Risk

Patients with hyponatremia are at an increased fall risk due to their muscle weakness, fatigue, and possible altered mental status. Make sure to have the bed alarm on these patients, and make sure they are wearing fall risk socks!

PHYSICAL Assessment

When performing a physical exam for a patient suspected of having hyponatremia, the nurse should assess for the following:

VITAL SIGNS

Checking vital signs is a fundamental part of a good physical assessment. In hyponatremia, blood pressure may be low if the condition is due to dehydration or high if it’s due to conditions like heart failure or kidney disease. Heart rate may be increased as the body tries to compensate for low blood pressure.

graphic of a brain

NEURO ASSESSMENT

Given that hyponatremia can significantly affect the nervous system, a detailed neurological examination is crucial. This may include checking for changes in mental status (such as confusion or lethargy) and even assessing gait and coordination. Severe hyponatremia can cause cerebral edema which may increase intracranial pressure (ICP). Pupillary assessment may show dilated pupils, decreased responsiveness to light, or asymmetry.

An illustration of the heart with the pulmonary and aortic vessels

CARDIO ASSESSMENT

This can help identify underlying heart conditions that may be causing hyponatremia, such as heart failure. An S3 can indicate fluid volume overload. Assessment of the peripheral extremities may show dependent edema or even JVD in the neck. Sodium abnormalities do not typically cause significant cardiac arrhythmias.

A very dry tongue, indicating dehydration and dry mucous membranes

SKIN ASSESSMENT

The skin can provide clues about the body’s hydration status. Dry skin or mucous membranes, sunken eyes, or decreased skin turgor (elasticity) can suggest dehydration, which is a common cause of hypotonic hyponatremia.

The physical assessment provides valuable information that can help healthcare providers identify the cause of hyponatremia and guide treatment decisions. In the following sections, we will explore the treatment and monitoring of hyponatremia.

Also check out: “The Cranial Nerve Assessment for Nurses”

Treatment for Hyponatremia:

The treatment of hyponatremia depends on what caused the hyponatremia, as treating the underlying cause is the actual treatment. In severe cases, typically nephrology is consulted on in these patients. Here are some key components of hyponatremia treatment:

The kidneys, with the left one transected so you can see the inside

ADDRESS UNDERLYING CAUSES

The first and main step in treating hyponatremia is to identify and manage any underlying conditions that may be causing the low sodium levels. This often involves fluid management, either increasing or decreasing fluids for the patient.

Calcium

IV FLUIDS

IV Fluids, like sodium chloride, have a good amount of sodium in them. However, these are ordered whenever there is a fluid deficit in the patient, which usually corrects the sodium since it corrects the underlying cause. Often fluid boluses may be used cautiously, followed by maintenance fluids until normal hydration and sodium levels are restored.

Calcium

FLUID RESTRICTION

Fluid restriction is a helpful first step in correcting sodium levels when the hyponatremia is due to excess water intake, retention, or fluid overload, fluid restriction is often the first line of treatment. This helps to gradually increase sodium levels in the blood.

SODIUM REPLACEMENT

Oral sodium tablets are sometimes used in patients, primarily those who do not have an adequate dietary intake of sodium or potomania, or if they are on medication that causes sodium wasting (like Lasix). SIADH can be treated with sodium tablets in addition to lasix and a fluid restriction. In acute or severe cases of hyponatremia, IV 3% hypertonic sodium may be administered. When 3% hypertonic saline is required, typically 100ml is given as a bolus over 10 minutes.

Bag of IV magnesium sulfate

MEDICATION

In cases of SIADH, certain medications which block ADH are used, called Vasopressin Receptor Antagonists. Urea can be administered in patients with SIADH, which causes an increased loss of electrolyte-free water.

How fast should you correct the sodium?

The goal of sodium correction should be to increase sodium levels by 4-6 mEq/L with the first 24 hours for most cases, although in severe cases can occur within 6 hours. Sodium should be corrected carefully. Acute hyponatremia (changes within 48 hours) can be corrected a little more aggressively, but correction should be especially cautious in chronic hyponatremia (changes > 48 hours). Correcting the sodium too fast can be associated with an irreversible condition called osmotic demyelination syndrome. Osmotic Demyelination Syndrome (ODS) is a serious neurological condition that can occur when sodium levels in the blood increase too rapidly. This is most commonly seen in the treatment of severe hyponatremia (low sodium levels). This condition leads to the destruction of the myelin sheath, a fatty layer that insulates nerve fibers in the brain. Preventing ODS involves careful and slow correction of sodium levels in patients with severe hyponatremia. To prevent this, Sodium should never be corrected more than 8mEq/L/24 hours in chronic hyponatremia to prevent this.

Monitoring of Hyponatremia

As a nurse, it is essential to monitor patients with hyponatremia closely to identify and manage any potential complications. The following parameters should be observed:

A Gold top blood vial filled with blood

LAB TESTS

Sodium levels should be checked occasionally, sometimes every 2-4 hours for severe cases, but at least every 24 hours. Other electrolytes should be checked, in addition to renal function tests.

graphic of a brain

NEURO STATUS

Regular neurological assessments should be performed to monitor for changes in consciousness, orientation, strength, and coordination. Any sudden changes, such as confusion, seizures, or loss of consciousness, should be reported immediately.

A graduated cylinder with urine in it

INTAKE & OUTPUT

Intake and output (I&Os) should be documented thoroughly to monitor the patient’s fluid balance.

As you can see, Hyponatremia is very complex, and we always have to be considering the underlying cause, which helps guide the treatment.  Remember, each patient is unique, and their care should be individualized based on their specific needs and circumstances. 

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