What is the treatment of hyponatremia?

Ans.

• When hypovolemic, 0.9% saline

• When hypervolemic, fluid restriction and sometimes a loop diuretic

• When euvolemic, treatment of the cause

• When severe hyponatremia, cautious correction with hypertonic (3%) saline. Rapid correction of hyponatremia, even mild hyponatremia, risks neurologic complications. Except possibly during the first few hours of treatment of severe

hyponatremia, Na should be corrected no faster than 0.5 mEq/L/h. Even in patients with severe hyponatremia, increase in serum Na concentration should not exceed 10 mEq/L over the first 24 hours. Any identified cause of hyponatremia is treated concurrently.

Mild hyponatremia: Mild, asymptomatic hyponatremia (i.e. serum Na>130 mEq/L) requires no saline because small adjustments are generally sufficient. In diuretic-induced hyponatremia, elimination of the diuretic may be enough; some patients need some Na replacement orally. Similarly, when mild hypo- natremia results from inappropriate hypotonic parenteral fluid administration in patients with impaired water excretion, merely altering fluid therapy may suffice. In patients with hypovolemia and normal adrenal function, administration of 0.9% saline usually corrects both hyponatremia and hypovolemia. In hypervolemic patients, in whom hyponatremia is due to renal Na retention (e.g. heart failure, cirrhosis, nephrotic syndrome) and dilution, water restriction combined with treatment of the underlying disorder is required. In patients with heart failure, an ACE inhibitor, in conjunction with a loop diuretic, can correct refractory hyponatremia. In other patients in whom simple fluid restriction is ineffective, a loop diuretic in escalating doses can be used, sometimes in conjunction with IV 0.9% normal saline. Potassium and other electrolytes lost in the urine must be replaced. When hyponatremia is more severe and unrespon-sive to diuretics, intermittent or continuous hemofiltration may be needed to control ECF volume while hyponatremia is corrected with IV 0.9% normal saline.

In euvolemia, treatment is directed at the cause (e.g. hypothyroidism, adrenal insufficiency). When SIADH is present, water restriction (e.g. 250 to 500 mL/24 h) is generally required. Additionally, a loop diuretic may be combined with IV 0.9% saline as in hypervolemic hyponatremia. Lasting correction depends on successful treatment of the underlying disorder. When the underlying disorder is not correctable and severe water restriction is not possible, demeclocycline (300–600 mg po q12 hour) may be helpful by inducing a concentrating defect in the kidneys. However, demeclocycline may cause acute renal failure which is usually reversible when the drug is stopped. Intravenous conivaptan, an ADH receptor antagonist, causes effective water diuresis without significant loss of electrolytes in the urine and can be used in hospitalized patients for treatment of resistant hyponatremia. Severe hyponatremia: Severe hyponatremia (serum Na < 120 mEq/L; effective osmolality < 238 mOsm/kg) in asymptomatic patients can be treated safely with stringent restriction of water intake. When neurologic symptoms (e.g. confusion, lethargy, seizures, coma) are present, IV 3% hypertonic saline should be given.

The pace and degree of hyponatremia correction should be carefully watched. Serum Na should be raised no faster than 1 mEq/L/h, but replacement rates of up to 2 mEq/L/hour for the first 2–3 hours may be given for patients with seizures. However, the rise should be ≤10–12 mEq/L over the first 24 hour. More rapid correction risks precipitation of osmotic demyelination syndrome. Hypertonic (3%) saline (containing 513 mEq Na/L) may be used, with frequent (q 2–4 h) electrolyte determinations. For patients with seizures or coma, ≤100 mL/h may be administered over 4–6 hours in amounts sufficient to raise the serum Na by 4–6 mEq/L.

Sodium correction: This amount (in mEq) may be calculated using the Na deficit formula as (Desired change in Na+) × TBW (where TBW is 0.6 × body weight in kg in men and 0.5 × body weight in kg in women). For example, the amount of Na needed to raise the Na from 104 to 110 in a 70 kg man can be calculated as follows: (110 mEq/L – 104 mEq/L) × (0.6 L/kg × 70 kg) = 252 mEq There is 513 mEq/L of Na in hypertonic saline, roughly 0.5 L of hypertonic saline is needed to raise the Na from 104 mEq/L to 110 mEq/L. This should be given over the succeeding 24 hours.

Adjustments may be needed based on serum Na+ concentrations, which are monitored closely during the first few hours of treatment. Patients with seizures, coma, or altered mental status need supportive treatment, which may involve endotracheal intubation, mechanical ventilation, and treatment for seizures.