Written by Dr.Md.Redwanul Huq (Masum)
Sunday, 15 January 2012 16:21



Hyponatremia is a clinical condition in which water concentration of the body is increased absolutely or relatively to the sodium (Na+) content.

Causes of hyponatraemia:

A. Hyponatraemia associated with decreased extracellular fluid(ECF) volume(i.e.depletional hyponatraemia):

1. Gastrointestinal tract (GIT) loss:

i) Diarrhea
ii) Vomiting
iii) Sequestration of fluid in bowel as in intestinal obstruction or paralytic ileus
iv) Fistula

2. Renal loss:

i) Addison’s disease
ii) Chronic renal failure,
iii) Salt losing nephropathy
iv) Use of excessive diuretics (e.g. osmotic diuretics)
v) Chronic interstitial nephritis
vi) Polycystic kidney disease

3. Cutaneous loss-

i) Severe burn
ii) Excessive sweating

4. Inadequate intake of salt due to environmental deprivation or inadequate therapeutic replacement

5.Metabolic acidosis.

B. Hyponatraemia associated with normal or slightly increased ECF volume:

1. Syndrome of inappropriate ADH secretion (SIADH) due to-

i) Bronchogenic carcinoma
ii) Carcinoma pancreas
iii) Dudenal carcinoma
iv) Cerebrovascular accident
v) Bronchietasis
vi) Pneumonia

2. Excessive intravenous fluid
3. Hypothyroidism
4. Psychogenic polydypsia.

C. Hyponatraemia associated with increased ECF volume: (i.e. dilutional hyponatraemia):

1. Cirrhosis of liver
2. Congestive cardiac failure
3. Nephrotic syndrome.

Symptoms of hyponatremia:

Symptoms of hyponatremia are as following-

i) Thirst
ii) Loss of appetite
iii) Nausea
iv) Vomiting
v) Weakness
vi) Dizziness on standing
vii) Convulsion
viii) Respiratory distress
ix) Muscle pain due to cramp.

Signs of hyponatremia:

In case of depletional hyponatraemia

  • Dryness of mouth
  • Weight loss
  • Pulse rate – increased
  • Postural hypotension
  • Low JVP
  • Reduced urine output
  • Reflexes- depressed
  • Confusion
  • Coma.

In case of hyponatraemia with normal ECF volume:

  • Dryness of mouth
  • Reflexes- depressed
  • Confusion
  • Coma.

In case of dilutional hyponatraemia:

  • Edema
  • Weight gain
  • JVP- raised
  • Ascites
  • Bilateral pleural effusion
  • Crepitations in lungs
  • Reflexes- depressed
  • Confusion
  • Coma.

Investigations of hyponatremia:

1. Serum electrolytes
2. Investigations to find out the underlying cause.

Treatment of hyponatremia:

Treatment of hyponatremia is as following-

1. Depletional hyponatraemia-

i) IV infusion of Normal saline (0.9% NaCl). If serum Na+ concentration is less than
125 mmol/L- 3% NaCl solution is given IV at a rate of 6-8 drops per minute
ii) Treatment of underlying cause.

2. Hyponatraemia with normal ECF-

i) Water restriction
ii) In case of severe hyponatraemia – loop diuretics and hypertonic solution are used

3. For dilutional hyponatraemia-

i) Restriction in Na+ and water intake
ii) 20% manitol- 100 ml to increase renal water excretion
iii) Treatment of underlying cause

N.B Calculation for Na+ requirement (in mmol) of the body-

(125 – measured Na+) X 0.6 X body weight in Kg.

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