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Hyponatremia (decreased serum sodium)

 
  By : , NJ, USA       13.7.2010         Phone:-          Fax:-          Mail Now
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Hyponatremia or decreased serum sodium occurs when serum sodium concentration is less than 136 meq/liter. Sodium is the main ion in the extracellular fluid compartment. Its metabolism is intertwined with water metabolism. 


Reduction in serum sodium can be classified into three categorizes: 
1) Hypovolemic hyponatremia- which is the reduction in both serum sodium and total body water.
2) Noromovolemic hyponatremia- where sodium is low but total body water is normal.
3) Hypervolemic hyponatremia- where sodium is low but total body water is increased. 

Causes

Hypovolemic hyponatremia
1) Gastrointestinal- diarrhea and vomiting, where fluid and sodium are lost
2) Kidney diseases- interstitial nephritis, polycystic kidney disease, medullary cystic disease, diuretics
3) Third spacing- in these situations, sodium and water are lost into different compartments of the body- such as:
a. Burns
b. Pancreatitis
c. Peritonitis
d. Intestinal obstruction

Normovolemic hyponatremia
1) medications- barbiturates, carbamazepine
2) adrenal disorders
3) hypothyroidism
4) SIADH or inappropriate secretion of antidiuretic hormone
5) Primary polydipsia- or drinking excess water
6) Pain
7) Stress
8) Post operative conditions

Hypervolemic hyponatremia
1) heart failure
2) cirrhosis
3) chronic kidney diseases such as nephrotic syndrome

Hyponatremia in AIDS
It is seen in about 50% of hospitalized AIDS patients. The etiology is unknown.

Symptoms

Older patients develop more symptoms than younger ones. Symptoms are more severe in cases of faster development of hyponatremia. In moderate hyponatremia, or above 115 meq/l, symptoms include:
- nausea
- headache
- lethargy or weakness
- confusion
- altered personalities

In severe cases, which are less than 115 meq/L, patients may show signs of:
- stupor/drowsiness
- neurological hyper excitability
- seizures
- coma
- Death.

In postmenopausal women, severe cerebral edema can occur.

Diagnosis

1) History- with identification of cause and physical examination.
2) serum and urine electrolytes
3) serum and urine osmolality
4) assessment of fluid status

Treatment

Identification of cause and type of hyponatremia is needed to determine method of treatment. In hypovolemic hyponatremia- 0.9% NaCl or normal saline should be given intravenously. In hypervolemic patients- fluid restriction and diuretics may be needed. In normovolemic hyponatremia- the cause should be treated. In some situations- 3% saline may be needed for treatment which should be given in a monitored, ICU setting. 

Complications of Treatment

Rapid correction of hyponatremia can cause neurological problems- such as brain demyelination. Hyponatremia should be corrected at the rate of 0.5 meq/L/hr. Correction should not be greater than 10 meq/L in 24 hrs.








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