Causes of hypovolemic hyponatremia:
- Gastrointestinal Sodium Loss: Vomiting, Diarrhea
- Renal Sodium Loss: Diuretic (esp. Thiazides)
- Skin Sodium Loss: Burns
Causes of Euvolemic hyponatremia:
- Primary polydipsia
- Excessive electrolytes-free water infusion
- SIADH (Syndrome of inappropriate secretion of antidiuretic hormone)
Causes of hypervolemia hyponatremia (Sodium retention with relatively greater water retention):
- Congestive cardiac failure
- Cirrhosis of liver
- Nephrotic syndrome
- Chronic Kidney Disease
Function of sodium
- Sodium accounts for 92% of ECF osmolarity and maintenance of the internal environment
- Sodium is concerned with resting membrane potential, action potential, and tissue excitability.
- Concerned with exocrine secretion
Clinical consequences of Hyponatremia
Most of the clinical effects of hyponatremia occur due to cellular overhydration i.e. (especially cerebral edema). Signs and symptoms start at a plasma sodium concentration less than 120 mmol/L. Initially, there was nausea, headache, lethargy, and malaise.
When the sodium level is less than 110 mmol/L, there will be drowsiness, confusion, stupor, coma, and even death.
Acute development of hyponatremia is more serious. Acute hyponatremia shows 29% incidence of convulsion and 50% mortality. Chronic development of hyponatremia is more tolerable because it allows time for osmotic adjustment between neurons and their surrounding ECF. So patient may be conscious even at plasma sodium less than 100 mmol/L. Chronic hyponatremia shows 4% incidence of Convulsion and 6% mortality.
Investigation done in hyponatremia
- Plasma electrolytes
- Plasma osmolarity
- Urine electrolytes
- Urine osmolality
- Measurement of plasma renin activity
Management of Hyponatremia with hypovolemic
The primary treatment of hyponatremia is the treatment of the primary cause. Oral electrolyte glucose mixture is given is mild hyponatremia with mild symptoms and advice to increase dietary salt intake.
- If the patient develops neurological signs, normal saline (0.9% NaCl) is infused
- 3% NaCl is infused if acute onset with neurological deficit
Management of hypervolemic hyponatremia with edema
For mild cases (Sodium 130 - 135 mmol/L), water restriction i.e. limit to 500 to 1500 ml per day with treatment of underlying disorder. For severe cases (Sodium < 124 mmol/L), continue water restriction and infusion of 3% hypertonic saline with diuretic therapy.
IV correction is done up to 126 mmol/L followed by oral correction. Not more than 10 mmol/kg body weight plasma sodium is corrected in a day.
The total sodium deficit is calculated by 0.6 x weight in Kg x (Desired sodium - Actual sodium).