hyponatremia



OVERVIEW

Definition.

Hyponatremia is a pathophysiologic state in which serum sodium is <135 mmol/L.

The serum sodium concentration is related to the total amount of sodium in the body, the amount of water, etc. A decrease in serum sodium concentration does not fully indicate a decrease in the total amount of sodium in the body.

The normal value of serum sodium ion is 135 to 145 mmol/L.

Sodium ion is the main cation of extracellular fluid (including intertissue fluid and blood, etc.), and its main role is to maintain the blood volume of extracellular fluid, maintain osmolality and acid-base balance, as well as to maintain the normal stress of muscles and nerves.

Classification

Classification according to blood sodium concentration

Mild hyponatremia: blood sodium 130～135mmol/L.

Moderate hyponatremia: blood sodium 125～129mmol/L.

Severe hyponatremia: blood sodium <125mmol/L.

Classification according to blood osmolality

Hypotonic hyponatremia: plasma osmolality <280mmol/L, is the most common type of hyponatremia; according to extracellular fluid volume, it can be further classified into hypovolemic, isovolemic and hypervolemic hyponatremia, with the volume of extracellular fluid being reduced, normal and increased, respectively.

Isotonic hyponatremia: plasma osmolality 280 to 295 mmol/L.

Hypertonic hyponatremia: plasma osmolality > 295 mmol/L.

Classification according to the time of onset

Acute hyponatremia: onset time <48 hours.

Chronic hyponatremia: those with onset time ≥48 hours. If the time of existence cannot be determined, chronic hyponatremia can be considered after excluding possible causes of acute hyponatremia.

Classification according to pathogenesis

Sodium-deficient hyponatremia: also known as hypotonic dehydration, where both extracellular fluid volume and total sodium are reduced and more sodium is lost than water.

Dilutional hyponatremia: i.e., water overload or water intoxication, extracellular fluid volume is increased, total sodium may be normal or increased, and intracellular fluid and serum sodium concentrations are decreased.

Metastatic hyponatremia: sodium moves from extracellular to intracellular, total sodium is normal, intracellular sodium increases, and serum sodium concentration decreases, more rarely.

Idiopathic hyponatremia: also known as consumptive hyponatremia, most commonly seen in malignant tumors, advanced cirrhosis, malnutrition, old age and other chronic diseases in the late stages of the disease, may be due to intracellular protein decomposition caused by a decrease in osmolality, water from the cell into the extracellular caused by the migration of water.

Cerebral salt-wasting syndrome: osmotic diuresis with decreased blood sodium, chloride, and potassium and increased urinary levels due to disruption of relevant neural connections as a result of injury.

Classification according to clinical symptoms

Mild symptomatic hyponatremia: any degree of decreased blood sodium with mild symptoms of hyponatremia such as inattention, irritability, personality changes, and depression.

Moderate symptomatic hyponatremia: any degree of decreased blood sodium with moderate hyponatremia symptoms such as nausea (without vomiting), confusion, and headache.

Severe symptomatic hyponatremia: any degree of decreased blood sodium with vomiting, cardiac respiratory distress, lethargy, seizures, coma (Glasgow Coma Score ≤ 8).

Morbidity.

The risk of hyponatremia is higher overall in the elderly and hospitalized: those ≥60 years of age have 2.54 times the risk of hyponatremia compared with those 13-60 years of age, and the prevalence of hyponatremia among hospitalized persons can be 15% to 30%.

The risk is higher in patients with hypertension, diabetes mellitus, stroke, coronary atherosclerotic heart disease, neoplasms, psychiatric disorders, and long-term continuous use of medications such as sodium-removing diuretics (e.g., furosemide, etanercept, etc.).

Causes

Causes

Hyponatremia can be caused by a variety of factors such as certain diseases, use of specific medications, and diet through different mechanisms.

Diseases

Chronic renal failure with polyuric phase, plasma extravasation during massive burns, prolonged gastrointestinal decompression, recurrent diarrhea, severe vomiting, massive pleural effusion, massive peritoneal effusion, etc., can result in excessive sodium loss causing hyponatremia.

Psychogenic irritability and thirst, decompensated stage of liver cirrhosis, oliguric stage of acute kidney injury, chronic renal failure, uremia, severe pain, hypoadrenocorticism, syndrome of dysregulated secretion of antidiuretic hormone, hyperglycemia, locomotor hyponatremia, hypothyroidism, inappropriate antidiuretic nephrotic syndrome, glucocorticoid deficiency, etc., can lead to the dilution of extracellular fluids and the occurrence of hyponatremia.

Tuberculosis, tumors, cirrhosis, malnutrition, and starvation can lead to hyponatremia due to depletion or inadequate intake.

Use of specific drugs

Heavy use of sodium-removing diuretics such as furosemide, etanercept, and thiazides can lead to excessive sodium loss.

Heavy use of drugs such as mannitol can cause extravasation of intracellular fluid, resulting in hyponatremia with dilution of extracellular fluid.

Inappropriate infusion of fluids can also lead to hyponatremia.

Diet

Excessive water intake can lead to blood dilution and hyponatremia.

Hyponatremia can also occur with prolonged low-sodium diets and inadequate sodium intake.

Other

Massive fluid loss due to plasmapheresis can cause hyponatremia.

Severe hyperlipidemia and hyperproteinemia can lead to pseudohyponatremia.

Pathogenesis

Hyponatremia is defined as a lower than normal serum sodium concentration. Disease, medications, diet, and other factors, can cause hyponatremia through the following mechanisms.

Excessive sodium loss

Sodium is present in fluids and is therefore generally accompanied by fluid loss or drainage.

Some fluids contain a high concentration of sodium (e.g., sweat), and when they are lost, a higher percentage of sodium is lost than water, and hyponatremia occurs.

Dilution of extracellular fluid

Hyponatremia can occur as a result of dilution of extracellular fluid due to the migration of intracellular water into extracellular fluid, or excessive water intake through diet or injection.

Increased osmolality of extracellular fluid and decreased osmolality of intracellular fluid can cause intracellular water to move into extracellular fluid.

Inadequate intake

Hyponatremia can occur if sodium intake is inadequate and the total amount of sodium in the body decreases.

Others

When the body is deficient in sodium, sodium moves from the extracellular to the intracellular, resulting in a decrease in serum sodium, an increase in intracellular sodium, and a normal or increased total sodium level.

Injury to the inferior colliculus or brainstem can result in disruption of the neural connection between the inferior colliculus and the kidneys, osmotic diuresis in the distal convoluted tubules, and a decrease in blood sodium.

Symptoms.

Hyponatremia is dominated by neurologic symptoms, and the severity of the symptoms is closely related to the blood sodium concentration and the rate of decline. Most of the symptoms of acute hyponatremia are obvious, and those with a primary disease may also have symptoms of the primary disease.

Main symptoms

Mild symptoms

May be manifested as fatigue, dizziness, numbness of hands and feet, inattention, irritability, personality change, depression and so on.

Moderate symptoms

Nausea (without vomiting), blurred vision, unsteady walking, fainting when getting up, blurred consciousness, headache, etc.

Significant decrease in urine output.

Severe symptoms

Spasmodic muscle cramps, vomiting, drowsiness, seizures, coma.

Complications

Hypovolemic shock

Hypovolemic shock can occur if there is a significant loss of body fluids and a marked reduction in blood volume, which may be manifested by vertigo on standing and cold extremities.

Subcutaneous edema

If the volume of body fluids is significantly increased, fluids can gather in the tissue interstitial space, resulting in subcutaneous edema, which is manifested as swelling and poor elasticity of the skin, and depressions can appear when pressed with fingers.

Cerebral edema, brain hernia

When there is a significant increase in fluid volume and a decrease in osmolality, the water in the extracellular fluid may move into the cells and cerebral edema may occur in the brain.

Pre-renal azotemia

If blood volume decreases, blood pressure may decrease, renal blood flow decreases, glomerular filtration rate decreases, and prerenal azotemia occurs.

Osmotic demyelination syndrome

People with chronic hyponatremia may develop neural demyelinating lesions if they are overcorrected too quickly and excessively.

Seek medical attention

Department of Medicine

Endocrinology

Prompt medical consultation is recommended for symptoms such as unexplained fatigue, numbness of hands and feet, nausea, and vomiting, especially if you have previously been on a long-term low-sodium diet or have an underlying condition that causes hyponatremia.

Emergency Department

When there are symptoms such as muscle spasmodic cramps, seizures, coma, etc., immediate consultation is recommended.

Preparation for medical treatment

Preparation for medical consultation: registration, preparation of documents, frequently asked questions

Tips for the doctor

In order to facilitate the doctor’s examination, ladies should try not to wear dresses.

In case of vomiting, you can use your cell phone to take a picture of the vomit for the doctor’s reference.

Preparation Checklist for Doctor’s Visit

Are there any unexplained fatigue, numbness in hands and feet, lack of concentration, irritability, personality change?

Are there nausea, vomiting, dizziness, headache, fainting easily when getting up, blurred consciousness?

Are the above symptoms recurring?

Are you allergic to drugs, food or other substances?

Are you suffering from hypertension, diabetes, hyperlipidemia, malignant tumors, cirrhosis of the liver, etc.?

Is there any long-term dieting or malnutrition?

Laboratory tests: blood electrolytes, urine electrolytes, plasma osmolality, blood routine, renal function, liver function, blood lipids

Imaging tests: cardiac ultrasound, abdominal ultrasound, cranial CT, cranial magnetic resonance imaging, abdominal CT

Other tests: electrocardiogram

Sodium-removing diuretics: furosemide, etanercept, hydrochlorothiazide

Osmotic diuretics: mannitol, sorbitol

Argipressin receptor antagonists: tolvaptan, rivastigmine, mozavaptan

Diagnosis

Diagnosis is based on

Hyponatremia can be diagnosed based on history, clinical signs, and laboratory tests. Laboratory tests and imaging can also help to identify the cause and vital organs.

Medical history

There may be severe vomiting, recurrent diarrhea, and prolonged and continuous use of sodium-removing diuretics.

There may be persistent overdrinking, congestive heart failure, malnutrition.

Clinical manifestations

Dizziness, headache, nausea, vomiting, blurred vision, and drowsiness may be present.

Physical examination may reveal manifestations such as diminished tendon reflexes.

Signs of dehydration such as decreased blood pressure and decreased skin elasticity may be seen in those with decreased blood volume.

Those with increased blood volume may show signs of overhydration such as weight gain and pale, moist skin.

Laboratory Tests

Serum sodium concentration can be clarified, and the diagnosis is clear if the blood sodium concentration is <135 mmol/L.

Can help determine the specific type of hyponatremia, including hypotonic, isotonic, and hypertonic.

Blood volume can be determined based on indicators such as hematocrit, hemoglobin volume, and hematocrit.

The above indicators may be elevated in those who are dehydrated; they may be decreased in those who are water intoxicated, and an increase in the mean volume of red blood cells may also be seen.

Urine sodium and other indicators can be monitored to help determine the condition and treatment effect.

Including blood biochemistry, urine routine, urine biochemistry, thyroid hormone level measurement, plasma brain natriuretic peptide, etc., which can help troubleshoot the underlying causes.

Imaging

Imaging mainly helps to understand the condition of various organs and troubleshoot the cause of the disease, commonly used are cardiac ultrasound, abdominal ultrasound, cranial CT, cranial magnetic resonance imaging, etc.

For those who may have cerebral edema or cerebral hernia, cranial CT and cranial magnetic resonance imaging can assist in diagnosis and clarify the condition.

Differential diagnosis

Hyponatremia can be clearly diagnosed by blood electrolyte analysis, and generally no differential is needed. The focus is on clarifying the cause of the disease through other tests, especially on detecting pseudo-hyponatremia caused by severe hyperlipidemia, hyperproteinemia, and so on.

Treatment

Hyponatremia requires clarification of osmolality, blood volume, and etiology, and is corrected by general treatment and medication according to the situation; meanwhile, the rate of correction should be reasonably controlled, and the primary disease should be actively treated.

General treatment

Stopping or restricting water intake: For mild high volume hyponatremia, temporary water abstinence or restriction of water intake may be required. Blood sodium level needs to be checked after a period of time to assess the effect of treatment; if the blood sodium level does not rise, medication such as diuretics may be needed.

Adjustment of medication: If sodium-removing diuretics are used, the medication can be adjusted according to the doctor’s instructions.

Adjustment of diet: chronic hyponatremia with low volume hypotonicity and mild hyponatremia can choose high sodium diet and increase the amount of salt in food appropriately.

Medication

Rehydration therapy

Rehydration therapy is suitable for people with low-volume hyponatremia, and for people with high-volume hypotonic hyponatremia, doctors need to be cautious about rehydration.

This is usually an intravenous sodium chloride solution.

When rehydration fluids are used to correct hyponatremia, frequent monitoring of blood sodium levels (once every 2 to 4 hours) is needed to prevent osmotic demyelination syndrome caused by too rapid correction of hyponatremia.

Diuretics.

Diuretics may be used at the request of a physician in cases of high volume hypotonic hyponatremia and antidiuretic hormone secretion dysregulation syndrome.

By promoting urination, blood volume can be lowered and symptoms improved.

Osmotic diuretics such as mannitol and sorbitol are mostly used, and drugs such as furosemide may also be used.

Argipressin receptor antagonists

Arginine pressin receptor antagonists include tolvaptan, rivastigmine, mozavaptan, and konivaptan.

These drugs antagonize the effects of arginine pressin, increase water clearance, and promote urinary excretion.

Tolvaptan is commonly used for significantly high and normal volume hyponatremia, as well as for hyponatremia that is poorly treated with water intake restriction; common adverse effects include thirst or dry mouth, and urinary frequency or polyuria.

Prognosis

Cure.

If the general condition is good, hyponatremia can mostly be corrected with prompt and effective treatment.

Severe hyponatremia that progresses rapidly has a high mortality rate.

Hazards

Symptoms of hyponatremia such as dizziness, headache, drowsiness and coma may affect normal life.

Severe acute hyponatremia can exacerbate pre-existing conditions and increase the rate of death.

Chronic hyponatremia corrected too quickly can lead to severe neurologic impairment, which can be life-threatening.

Hyponatremia may increase the risk of falls and fractures in the elderly and induce various underlying diseases and complications.

Daily

Daily Management

Dietary management

Limit water intake or increase salt intake as prescribed by your doctor during treatment.

If there are no diseases requiring sodium restriction such as hypertension or heart failure, it is recommended to maintain a normal diet and avoid a prolonged low-sodium or even no-sodium diet.

Drink water in moderation, do not ingest a large amount of water at one time. When hydration is needed due to profuse sweating, etc., saline can be chosen to prevent water intoxication.

Life management

If there is dizziness, headache, weakness, etc., you should rest in bed to prevent injuries such as falls.

After recovery, you can move moderately according to your condition.

Prevention

A nutritionally balanced diet is good for health. Do not go on a long-term low-sodium or no-sodium diet, or even fasting, without a doctor’s advice.

Those who have been treated with sodium-discharging diuretics for a long time, as well as those who have chronic renal failure, heart failure and other underlying diseases, should follow the doctor’s requirements for medication and treatment, as well as regular follow-ups and monitoring of blood sodium levels, etc., to prevent hyponatremia.

When exercising, attention should be paid to the degree of intensity. Exercise hyponatremia may occur during and after marathons, triathlons and other endurance-demanding exercises, so it is best to consult a doctor before exercising, and pay attention to the reasonable replenishment of water and electrolytes during exercise.