Hiponatremi , Hyponatremia

Treatment

Rapid correction of hyponatremia, even mild hyponatremia, risks neurologic complications  Generally, Na should be corrected no faster than 0.5 mEq/L/h. Increase should not exceed 10 mEq/L over the first 24 h. Any identified cause of hyponatremia is treated concurrently.

Mild hyponatremia: Mild, asymptomatic hyponatremia (ie, plasma Na > 120 mEq/L) requires restraint. In diuretic-induced hyponatremia, elimination of the diuretic may be enough; some patients need some Na or K replacement. Similarly, if mild hyponatremia results from inappropriate parenteral fluid administration in a patient with impaired water excretion, merely stopping hypotonic fluid therapy may suffice.

With hypovolemia, if adrenal function is normal, administration of 0.9% saline usually corrects both hyponatremia and hypovolemia. If the plasma Na is < 120 mEq/L, it may not completely correct upon restoration of intravascular volume; restriction of free water ingestion to ≤ 500 to 1000 mL/24 h may be needed.

In hypervolemic patients, in whom dilutional hyponatremia is due to renal Na retention (eg, heart failure, cirrhosis, nephrotic syndrome), water restriction combined with treatment of the underlying disorder is often successful. An ACE inhibitor, in conjunction with a loop diuretic, can correct refractory hyponatremia in patients with heart failure. If hyponatremia does not respond to simple fluid restriction, a loop diuretic in escalating doses can be used, sometimes in conjunction with IV 0.9% normal saline. K and other electrolytes lost in the urine must be replaced. If hyponatremia is severe and unresponsive 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 (eg, hypothyroidism, adrenal insufficiency, diuretic use). If SIADH is present, severe water restriction (eg, 250 to 500 mL/24 h) is 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 disease. When the underlying disease is not treatable, as in metastatic lung cancer, and severe water restriction is unacceptable to the patient, demeclocycline (300 to 600 mg q 12 h) may be helpful; however, demeclocycline may cause acute renal failure; renal failure is usually reversible when the drug is stopped. Investigational selective vasopressinSome Trade Names
PITRESSIN

receptor antagonists effectively produce water diuresis without significant loss of electrolytes in the urine and may provide useful future treatment for resistant hyponatremia.

Severe hyponatremia: Severe hyponatremia (plasma Na < 109 mEq/L; effective osmolality < 238 mOsm/kg) in asymptomatic patients can be treated safely with stringent restriction of water intake. Treatment is more controversial when neurologic symptoms (eg, confusion, lethargy, seizures, coma) are present. The debate primarily concerns the pace and degree of hyponatremia correction. Many experts recommend that plasma Na be raised no faster than 1 mEq/L/h, but replacement rates of up to 2 mEq/L/h for the first 2 to 3 h have been suggested for patients with seizures. Regardless, the rise should be ≤ 10 mEq/L over the first 24 h. More vigorous correction risks precipitation of osmotic demyelination syndrome (see below).

Hypertonic (3%) saline (containing 513 mEq Na/L) may be used, but only with frequent (q 2 to 4 h) electrolyte determinations. For patients with seizures or coma, ≤ 100 mL/h may be administered over 4 to 6 h in amounts sufficient to raise the serum Na 4 to 6 mEq/L. 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 106 to 112 in a 70-kg man can be calculated as follows:

(112 mEq/L − 106 mEq/L) × (0.6 L/kg × 70 kg) = 252 mEq.

Because there is 513 mEq Na/L in hypertonic saline, roughly 0.5 L of hypertonic saline is needed to raise the Na from 106 to 112 mEq/L. Adjustments may be needed, so plasma Na must be monitored closely, beginning within the first 2 to 3 h after initiation of treatment. Patients with seizures, coma, or altered mental status need supportive treatment, which may involve airway intubation and benzodiazepines (eg, lorazepamSome Trade Names
ATIVAN

1 to 2 mg IV q 5 to 10 min prn) for seizures.

Osmotic demyelination syndrome: Osmotic demyelination syndrome (previously called central pontine myelinolysis) may follow too-rapid correction of hyponatremia. Demyelination may affect the pons and other areas of the brain. Lesions are more common in patients with alcoholism, malnutrition, or other chronic debilitating illness. Flaccid paralysis, dysarthria, and dysphagia can evolve over a few days or weeks. The lesion may extend dorsally to involve sensory tracts and leave the patient with a locked-in syndrome (an awake and sentient state in which the patient, because of generalized motor paralysis, cannot communicate, except possibly by coded eye movements). Damage often is permanent. If Na is replaced too rapidly (eg, > 14 mEq/L/8 h) and neurologic symptoms start to develop, it is critical to prevent further plasma Na increases by stopping hypertonic fluids. In such cases, inducing hyponatremia with hypotonic fluid may mitigate the development of permanent neurologic damage.

Prof. Dr. Yusuf AKCAN Gastroenteroloji Uzm. Ozel Istanbul Onkoloji Hastanesi Tel. : 0 530 286 29 80 Tel. : 0 532 652 52 06   Cevizli Mah. Toros Cad. No : 86 PK:34846 Maltepe / Istanbul ( Gulsuyu Metro duragi karsisi)