Hyponatremia
Hyponatremia | |
---|---|
Other names | Hyponatraemia, low blood sodium, hyponatræmia |
high volume[4] | |
Diagnostic method | Serum sodium < 135 mmol/L[3] |
Differential diagnosis | Ethanol intoxication or withdrawal, high protein levels, high blood fat levels, high blood sugar[5][6] |
Treatment | Based on underlying cause[4] |
Frequency | Relatively common[6][7] |
Hyponatremia or hyponatraemia is a low concentration of
The causes of hyponatremia are typically classified by a person's body fluid status into
Treatment is based on the underlying cause.
Hyponatremia is the most common type of
Signs and symptoms
Signs and symptoms of hyponatremia include
Symptom severity depends on how fast and how severe the drop in blood sodium level is. A gradual drop, even to very low levels, may be tolerated well if it occurs over several days or weeks, because of neuronal adaptation. The presence of underlying neurological disease such as a seizure disorder or non-neurological metabolic abnormalities, also affects the severity of neurologic symptoms.
Chronic hyponatremia can lead to such complications as neurological impairments. These neurological impairments most often affect gait (walking) and attention, and can lead to increased reaction time and falls.[citation needed] Hyponatremia, by interfering with bone metabolism, has been linked with a doubled risk of osteoporosis and an increased risk of bone fracture.[18]
Causes
The specific causes of hyponatremia are generally divided into those with
High volume
Both sodium and water content increase: Increase in sodium content leads to hypervolemia and water content to hyponatremia.
- Cirrhosis of the liver[12]
- Congestive heart failure[12]
- Nephrotic syndrome in the kidneys[12]
- Excessive water consumption (Water intoxication)[12]
Normal volume
There is volume expansion in the body, no edema, but hyponatremia occurs[19]
- SIADH (and its many causes)[12]
- Hypothyroidism[12]
- Not enough ACTH[12]
- Beer potomania
- Normal physiologic change of pregnancy[20][21]
- Reset osmostat
Low volume
Hypovolemia (extracellular volume loss) is due to total body sodium loss. Hyponatremia is caused by a relatively smaller loss in total body water.[19]
- Any cause of hypovolemia such as prolonged vomiting, decreased oral intake, severe diarrhea[12]
- Diuretic use (due to the diuretic causing a volume depleted state and thence ADH release, and not a direct result of diuretic-induced urine sodium loss)[12]
- mineralocorticoid deficiency)[12]
- Isolated hyperchlorhidrosis (Carbonic anhydrase XII deficiency), a rare genetic disorder which results in a lifelong tendency to lose excessive amounts of sodium by sweating.
- Pancreatitis[12]
- Prolonged exercise and sweating, combined with drinking water without electrolytes is the cause of exercise-associated hyponatremia (EAH).[5][22] It is common in marathon runners and participants of other endurance events.[23]
- The use of MDMA (ecstasy) can result in hyponatremia.[24]
Medication
Available evidence suggests that all classes of
Other causes
Miscellaneous causes that are not included under the above classification scheme include the following:
- False or pseudo hyponatremia is caused by a false lab measurement of sodium due to massive increases in blood immunoglobulins as may occur in multiple myeloma.[12]
- Hyponatremia with elevated tonicity can occur with high blood sugar, causing a shift of excess free water into the serum.[12]
Pathophysiology
The causes of and treatments for hyponatremia can only be understood by having a grasp of the size of the
Normal homeostasis
There is a hypothalamic-kidney feedback system which normally maintains the concentration of the serum sodium within a narrow range. This system operates as follows: in some of the cells of the
Hyponatremia
Hyponatremia occurs 1) when the hypothalamic-kidney feedback loop is overwhelmed by increased fluid intake, 2) the feedback loop malfunctions such that ADH is always "turned on", 3) the receptors in the kidney are always "open" regardless of there being no signal from ADH to be open; or 4) there is an increased ADH even though there is no normal stimulus (elevated serum sodium) for ADH to be increased.
Hyponatremia occurs in one of two ways: either the osmoreceptor-aquaporin feedback loop is overwhelmed, or it is interrupted. If it is interrupted, it is either related or not related to ADH.
Sodium is the primary positively charged ion outside of the cell and cannot cross from the interstitial space into the cell. This is because charged sodium ions attract around them up to 25 water molecules, thereby creating a large
Diagnosis
The history, physical exam, and laboratory testing are required to determine the underlying cause of hyponatremia. A blood test demonstrating a serum sodium less than 135 mmol/L is diagnostic for hyponatremia.[34] The history and physical exam are necessary to help determine if the person is hypovolemic, euvolemic, or hypervolemic, which has important implications in determining the underlying cause. An assessment is also made to determine if the person is experiencing symptoms from their hyponatremia. These include assessments of alertness, concentration, and orientation.
False hyponatremia
False hyponatremia, also known as spurious, pseudo, hypertonic, or artifactual hyponatremia is when the lab tests read low sodium levels but there is no
True hyponatremia
True hyponatremia, also known as hypotonic hyponatremia, is the most common type. It is often simply referred to as "hyponatremia." Hypotonic hyponatremia is categorized in 3 ways based on the person's blood volume status. Each category represents a different underlying reason for the increase in ADH that led to the water retention and thence hyponatremia:
- High volume hyponatremia, wherein there is decreased congestive heart failure, liver failure, or kidney disease.
- Normal volume hyponatremia, wherein the increase in ADH is secondary to either physiologic but excessive ADH release (as occurs with nausea or severe pain) or inappropriate and non-physiologic secretion of ADH, that is, syndrome of inappropriate antidiuretic hormone hypersecretion (SIADH). Often categorized under euvolemic is hyponatremia due to inadequate urine solute (not enough chemicals or electrolytes to produce urine) as occurs in beer potomania or "tea and toast" hyponatremia, hyponatremia due to hypothyroidism or central adrenal insufficiency, and those rare instances of hyponatremia that are truly secondary to excess water intake.
- Low volume hyponatremia, wherein ADH secretion is stimulated by or associated with volume depletion (not enough water in the body) due to decreased effective circulating volume.
Acute versus chronic
Chronic hyponatremia is when sodium levels drop gradually over several days or weeks and symptoms and complications are typically moderate. Chronic hyponatremia is often called asymptomatic hyponatremia in clinical settings because it is thought to have no symptoms; however, emerging data suggests that "asymptomatic" hyponatremia is not actually asymptomatic.[14]
Acute hyponatremia is when sodium levels drop rapidly, resulting in potentially dangerous effects, such as rapid brain swelling, which can result in coma and death.
Treatment
The treatment of hyponatremia depends on the underlying cause.[12] How quickly treatment is required depends on a person's symptoms.[12] Fluids are typically the cornerstone of initial management.[12] In those with severe disease an increase in sodium of about 5 mmol/L over one to four hours is recommended.[12] A rapid rise in serum sodium is anticipated in certain groups when the cause of the hyponatremia is addressed thus warranting closer monitoring in order to avoid overly rapid correction of the blood sodium concentration. These groups include persons who have hypovolemic hyponatremia and receive intravenous fluids (thus correcting their hypovolemia), persons with adrenal insufficiency who receive hydrocortisone, persons in whom a medication causing increased ADH release has been stopped, and persons who have hyponatremia due to decreased salt and/or solute intake in their diet who are treated with a higher solute diet.[16] If large volumes of dilute urine are seen, this can be a warning sign that overcorrection is imminent in these individuals.[16]
Sodium deficit = (140 – serum sodium) × total body water[5]
Total body water = kilograms of body weight × 0.6
Fluids]
Options include:
- Mild and asymptomatic hyponatremia is treated with adequate solute intake (including salt and protein) and fluid restriction starting at 500 millilitres per day (mL/d) of water with adjustments based on serum sodium levels. Long-term fluid restriction of 1,200–1,800 mL/d may maintain the person in a symptom-free state.[36]
- Moderate and/or symptomatic hyponatremia is treated by raising the serum sodium level by 0.5 to 1 mmol per liter per hour for a total of 8 mmol per liter during the first day with the use of furosemide and replacing sodium and potassium losses with 0.9% saline.
- Severe hyponatremia or severe symptoms (confusion, convulsions, or coma): consider hypertonic saline (3%) 1–2 mL/kg IV in 3–4 h. Hypertonic saline may lead to a rapid dilute diuresis and fall in the serum sodium. It should not be used in those with an expanded extracellular fluid volume.
Electrolyte abnormalities
In persons with hyponatremia due to low blood volume (hypovolemia) from diuretics with simultaneous low blood potassium levels, correction of the low potassium level can assist with correction of hyponatremia.[16]
Medications
American and European guidelines come to different conclusions regarding the use of medications.[37] In the United States they are recommended in those with SIADH, cirrhosis, or heart failure who fail limiting fluid intake.[37] In Europe they are not generally recommended.[37]
There is tentative evidence that vasopressin receptor antagonists (vaptans), such as conivaptan, may be slightly more effective than fluid restriction in those with high volume or normal volume hyponatremia.[4] They should not be used in people with low volume.[12] They may also be used in people with chronic hyponatremia due to SIADH that is insufficiently responsive to fluid restriction and/or sodium tablets.[16]
Daily use of urea by mouth, while not commonly used due to the taste, has tentative evidence in SIADH.[12][38] However, it is not available in many areas of the world.[12]
Precautions
Raising the serum sodium concentration too rapidly may cause osmotic demyelination syndrome.[39][40][41] Rapid correction of sodium levels can also lead to central pontine myelinolysis (CPM).[42] It is recommended not to raise the serum sodium by more than 10 mEq/L/day.[43]
Epidemiology
Hyponatremia is the most commonly seen
People who have hyponatremia who require hospitalisation have a longer length of stay (with associated increased costs) and also have a higher likelihood of requiring readmission. This is particularly the case in men and in the elderly.[44]
References
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Further reading
- Sandy Craig; Erik D Schraga; Francisco Talavera; Howard A Bessen; John D Halamka (2010-04-13). "Hyponatremia in Emergency Medicine". Medscape.
- Kugler JP, Hustead T (June 2000). "Hyponatremia and hypernatremia in the elderly". Am Fam Physician. 61 (12): 3623–30. PMID 10892634. Archived from the originalon 2011-06-06. Retrieved 2011-05-15.
- James L. Lewis, III, MD (May 2009). "Hyponatremia". Merck Manual of Diagnosis and Therapy. Archived from the original on 2011-01-11. Retrieved 2011-05-15.
{{cite web}}
: CS1 maint: multiple names: authors list (link) - Elizabeth Quinn (2011-03-07). "What Is Hyponatremia: Hyponatremia or water intoxication – Can Athletes Drink Too Much Water?". About.com. Archived from the originalon 2009-10-28. Retrieved 2009-08-16.
External links
- Hyponatremia at the Mayo Clinic
- Sodium at Lab Tests Online
- ICD-10 code for Hyponatremia - Diagnosis Code